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Michel Baum - One of the best experts on this subject based on the ideXlab platform.
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novel amiloride sensitive sodium dependent proton secretion in the mouse Proximal Convoluted Tubule
Journal of Clinical Investigation, 2000Co-Authors: Joo Young Choi, Mehul Shah, Patrick J Schultheis, Gary E Shull, Shmuel Muallem, Michel BaumAbstract:: The Proximal Convoluted Tubule (PCT) reabsorbs most of the filtered bicarbonate. Proton secretion is believed to be mediated predominantly by an apical membrane Na(+)/H(+) exchanger (NHE). Several NHE isoforms have been cloned, but only NHE3 and NHE2 are known to be present on the apical membrane of the PCT. Here we examined apical membrane PCT sodium-dependent proton secretion of wild-type (NHE3(+/+)/NHE2(+/+)), NHE3(-/-), NHE2(-/-), and double-knockout NHE3(-/-)/NHE2(-/-) mice to determine their relative contribution to luminal proton secretion. NHE2(-/-) and wild-type mice had comparable rates of sodium-dependent proton secretion. Sodium-dependent proton secretion in NHE3(-/-) mice was approximately 50% that of wild-type mice. The residual sodium-dependent proton secretion was inhibited by 100 microM 5-(N-ethyl-N-isopropyl) amiloride (EIPA). Luminal sodium-dependent proton secretion was the same in NHE3(-/-)/NHE2(-/-) as in NHE3(-/-) mice. These data point to a previously unrecognized Na(+)-dependent EIPA-sensitive proton secretory mechanism in the Proximal Tubule that may play an important role in acid-base homeostasis.
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inhibition of Proximal Convoluted Tubule transport by dopamine
Kidney International, 1998Co-Authors: Michel Baum, Raymond QuigleyAbstract:Inhibition of Proximal Convoluted Tubule transport by dopamine. Background Dopamine can produce a natriuresis and diuresis independent of changes in renal hemodynamics. However, previous studies have failed to demonstrate an inhibition of transport by dopamine in intact Proximal Convoluted Tubules. Methods Rabbit Proximal Convoluted Tubules were perfused in vitro with an ultrafiltrate-like solution and bathed in a serum-like albumin solution. Results In the present study, the addition of 10 -5 m dopamine to the lumen or bath of Proximal Convoluted Tubules perfused in vitro had no effect on transport. In Proximal Convoluted Tubules, addition of 10 -6 m bath norepinephrine increased the rate of volume absorption from 0.65 ± 0.08 to 0.93 ± 0.08nl/mm · min ( P -5 m luminal dopamine in the presence of bath norepinephrine inhibited the rate of volume absorption to 0.72 ± 0.10nl/mm · min ( P = 0.01). The inhibition in the rate of volume absorption by luminal dopamine in the presence of bath norepinephrine was completely blocked by the DA 1 antagonist, SCH 23390. The DA 1 agonist luminal 10 -5 m fenoldopam also inhibited volume absorption in the presence of bath norepinephrine, but the DA 2 agonist luminal 10 -5 m quinpirole was without effect. Bath 10 -5 m dopamine had no effect on volume absorption in the presence of bath norepinephrine. Conclusion Dopamine has no direct epithelial action on the Proximal Convoluted Tubule. However, luminal dopamine antagonizes the stimulation in transport produced by norepinephrine. These studies suggest that luminal dopamine may play a role to modulate sodium transport in the presence of renal nerve activity.
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effect of luminal angiotensin ii on rabbit Proximal Convoluted Tubule bicarbonate absorption
American Journal of Physiology-renal Physiology, 1997Co-Authors: Michel Baum, Raymond Quigley, Albert QuanAbstract:The present in vitro microperfusion study examined the effect of luminal angiotensin II on Proximal Convoluted Tubule (PCT) volume absorption and bicarbonate transport. Neither 10−11 M, 10−10 M, no...
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maturation of rabbit Proximal Convoluted Tubule chloride permeability
Pediatric Research, 1996Co-Authors: Ji Nan Sheu, Michel Baum, Geeta Bajaj, Raymond QuigleyAbstract:Chloride transport in the rabbit Proximal Convoluted Tubule (PCT) has components of active, transcellular, and passive, paracellular transport. The preferential reabsorption of bicarbonate and organic solutes by the early Proximal Tubule leaves the luminal fluid with a higher chloride concentration than that in the peritubular capillaries. Previous studies have suggested that solute permeability of the paracellular pathway may be higher in the neonatal PCT and that the neonatal Proximal Tubule reabsorbs solutes by passive mechanisms to a greater extent than the adult segment. A higher chloride permeability would provide a mechanism for the greater rate of passive NaCl transport by the neonatal Proximal Tubule. The purpose of the present in vitro microperfusion study was to directly examine the chloride permeability of neonatal and adult PCT. Superficial and juxtamedullary, neonatal and adult PCT were perfused with a high chloride perfusate without organic solutes, simulating late Proximal tubular fluid, at 20°C, and bathed in a serum-like albumin solution. Chloride concentrations in the perfusate and the collected fluid were measured by electrometric titration. Neonatal juxtamedullary PCT chloride permeability (P Cl ) was significantly lower than adult juxtamedullary PCT P Cl (0.15 ± 0.25 X 10 -5 cm/s versus 5.23 ± 0.57 X 10 -5 cm/s, p < 0,001). The P Cl of neonatal superficial PCT was not different from that of adult superficial PCT (0.81 ± 0.48 X 10 -5 cm/s versus 0.05 ± 0.62 X 10 cm/s). Thus, there is a maturational increase in juxtamedullary PCT P Cl , whereas superficial PCT P Cl remains very low. The passive diffusion of chloride in neonatal PCT is extremely low and is not a mechanism to explain a higher rate of passive NaCl transport in this segment.
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stimulation of Proximal Convoluted Tubule phosphate transport by epidermal growth factor signal transduction
American Journal of Physiology-renal Physiology, 1995Co-Authors: Raymond Quigley, Donald A Kennerly, Ji Nan Sheu, Michel BaumAbstract:The present study investigated the signal-transduction pathway responsible for the epidermal growth factor (EGF) stimulation of phosphate transport (JPhos) in the rabbit Proximal Convoluted Tubule (PCT). Genistein, 10(-4) M, bath and lumen, an inhibitor of EGF receptor tyrosine kinase activity, blocked the EGF effect on JPhos, consistent with a role for tyrosine kinase in the signal-transduction pathway. Both staurosporine (5 x 10(-8) M) and calphostin C (10(-8) M), inhibitors of protein kinase C, blocked the EGF stimulation of JPhos, indicating that protein kinase C is involved in EGF signaling. Intracellular calcium (Ca2+i) concentrations were measured in perfused Tubules using fura PE3 to determine whether changes in Ca2+i were also part of the signaling pathway. After addition of 3 nM EGF, there was no change in Ca2+i, suggesting that stimulation of protein kinase C is not from phosphatidylinositol hydrolysis by phospholipase C-gamma. To determine whether phospholipase A2 (PLA2) is involved, the inhib...
Raymond Quigley - One of the best experts on this subject based on the ideXlab platform.
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inhibition of Proximal Convoluted Tubule transport by dopamine
Kidney International, 1998Co-Authors: Michel Baum, Raymond QuigleyAbstract:Inhibition of Proximal Convoluted Tubule transport by dopamine. Background Dopamine can produce a natriuresis and diuresis independent of changes in renal hemodynamics. However, previous studies have failed to demonstrate an inhibition of transport by dopamine in intact Proximal Convoluted Tubules. Methods Rabbit Proximal Convoluted Tubules were perfused in vitro with an ultrafiltrate-like solution and bathed in a serum-like albumin solution. Results In the present study, the addition of 10 -5 m dopamine to the lumen or bath of Proximal Convoluted Tubules perfused in vitro had no effect on transport. In Proximal Convoluted Tubules, addition of 10 -6 m bath norepinephrine increased the rate of volume absorption from 0.65 ± 0.08 to 0.93 ± 0.08nl/mm · min ( P -5 m luminal dopamine in the presence of bath norepinephrine inhibited the rate of volume absorption to 0.72 ± 0.10nl/mm · min ( P = 0.01). The inhibition in the rate of volume absorption by luminal dopamine in the presence of bath norepinephrine was completely blocked by the DA 1 antagonist, SCH 23390. The DA 1 agonist luminal 10 -5 m fenoldopam also inhibited volume absorption in the presence of bath norepinephrine, but the DA 2 agonist luminal 10 -5 m quinpirole was without effect. Bath 10 -5 m dopamine had no effect on volume absorption in the presence of bath norepinephrine. Conclusion Dopamine has no direct epithelial action on the Proximal Convoluted Tubule. However, luminal dopamine antagonizes the stimulation in transport produced by norepinephrine. These studies suggest that luminal dopamine may play a role to modulate sodium transport in the presence of renal nerve activity.
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effect of luminal angiotensin ii on rabbit Proximal Convoluted Tubule bicarbonate absorption
American Journal of Physiology-renal Physiology, 1997Co-Authors: Michel Baum, Raymond Quigley, Albert QuanAbstract:The present in vitro microperfusion study examined the effect of luminal angiotensin II on Proximal Convoluted Tubule (PCT) volume absorption and bicarbonate transport. Neither 10−11 M, 10−10 M, no...
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maturation of rabbit Proximal Convoluted Tubule chloride permeability
Pediatric Research, 1996Co-Authors: Ji Nan Sheu, Michel Baum, Geeta Bajaj, Raymond QuigleyAbstract:Chloride transport in the rabbit Proximal Convoluted Tubule (PCT) has components of active, transcellular, and passive, paracellular transport. The preferential reabsorption of bicarbonate and organic solutes by the early Proximal Tubule leaves the luminal fluid with a higher chloride concentration than that in the peritubular capillaries. Previous studies have suggested that solute permeability of the paracellular pathway may be higher in the neonatal PCT and that the neonatal Proximal Tubule reabsorbs solutes by passive mechanisms to a greater extent than the adult segment. A higher chloride permeability would provide a mechanism for the greater rate of passive NaCl transport by the neonatal Proximal Tubule. The purpose of the present in vitro microperfusion study was to directly examine the chloride permeability of neonatal and adult PCT. Superficial and juxtamedullary, neonatal and adult PCT were perfused with a high chloride perfusate without organic solutes, simulating late Proximal tubular fluid, at 20°C, and bathed in a serum-like albumin solution. Chloride concentrations in the perfusate and the collected fluid were measured by electrometric titration. Neonatal juxtamedullary PCT chloride permeability (P Cl ) was significantly lower than adult juxtamedullary PCT P Cl (0.15 ± 0.25 X 10 -5 cm/s versus 5.23 ± 0.57 X 10 -5 cm/s, p < 0,001). The P Cl of neonatal superficial PCT was not different from that of adult superficial PCT (0.81 ± 0.48 X 10 -5 cm/s versus 0.05 ± 0.62 X 10 cm/s). Thus, there is a maturational increase in juxtamedullary PCT P Cl , whereas superficial PCT P Cl remains very low. The passive diffusion of chloride in neonatal PCT is extremely low and is not a mechanism to explain a higher rate of passive NaCl transport in this segment.
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stimulation of Proximal Convoluted Tubule phosphate transport by epidermal growth factor signal transduction
American Journal of Physiology-renal Physiology, 1995Co-Authors: Raymond Quigley, Donald A Kennerly, Ji Nan Sheu, Michel BaumAbstract:The present study investigated the signal-transduction pathway responsible for the epidermal growth factor (EGF) stimulation of phosphate transport (JPhos) in the rabbit Proximal Convoluted Tubule (PCT). Genistein, 10(-4) M, bath and lumen, an inhibitor of EGF receptor tyrosine kinase activity, blocked the EGF effect on JPhos, consistent with a role for tyrosine kinase in the signal-transduction pathway. Both staurosporine (5 x 10(-8) M) and calphostin C (10(-8) M), inhibitors of protein kinase C, blocked the EGF stimulation of JPhos, indicating that protein kinase C is involved in EGF signaling. Intracellular calcium (Ca2+i) concentrations were measured in perfused Tubules using fura PE3 to determine whether changes in Ca2+i were also part of the signaling pathway. After addition of 3 nM EGF, there was no change in Ca2+i, suggesting that stimulation of protein kinase C is not from phosphatidylinositol hydrolysis by phospholipase C-gamma. To determine whether phospholipase A2 (PLA2) is involved, the inhib...
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glucocorticoids stimulate rabbit Proximal Convoluted Tubule acidification
Journal of Clinical Investigation, 1993Co-Authors: Michel Baum, Raymond QuigleyAbstract:Abstract Glucocorticoids have an important role in renal acidification; however, a direct effect of glucocorticoids on Proximal Convoluted Tubule (PCT) acidification has not been directly demonstrated. In the present in vitro microperfusion study PCT from animals receiving dexamethasone (600 micrograms/kg twice daily for 2 d and 2 h before killing) had a significantly higher rate of bicarbonate absorption than did controls (92.0 +/- 13.3 vs 59.9 +/- 3.2 pmol/mm.min, P < 0.01). To examine if glucocorticoids had a direct epithelial action, dexamethasone was added to the bath of PCT perfused in vitro. After 3 h of incubation in paired experiments 10(-6) M and 10(-5) M dexamethasone resulted in an approximately 30% stimulation in the rate of bicarbonate absorption. 10(-7) M dexamethasone and 10(-6) M aldosterone had no effect on bicarbonate absorption. The stimulation of acidification by 10(-5) M dexamethasone was blocked by actinomycin D and cycloheximide. These data are consistent with a direct effect of glucocorticoids on PCT acidification, and this effect is dependent upon protein synthesis.
Herve Favre - One of the best experts on this subject based on the ideXlab platform.
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protein kinase a induces recruitment of active na k atpase units to the plasma membrane of rat Proximal Convoluted Tubule cells
The Journal of Physiology, 1998Co-Authors: Maria Luisa Carranza, Martine Rousselot, Herve Favre, Alejandro M Bertorello, Alexander V Chibalin, Eric FerailleAbstract:1The aim of this study was to investigate the mechanism of control of Na+,K+-ATPase activity by the cAMP-protein kinase A (PKA) pathway in rat Proximal Convoluted Tubules. For this purpose, we studied the in vitro action of exogenous cAMP (10−3 M dibutyryl-cAMP (db-cAMP) or 8-bromo-cAMP) and endogenous cAMP (direct activation of adenylyl cyclases by 10−5 M forskolin) on Na+,K+-ATPase activity and membrane trafficking. 2PKA activation stimulated both the cation transport and hydrolytic activity of Na+,K+-ATPase by about 40 %. Transport activity stimulation was specific to the PKA signalling pathway since (1) db-cAMP stimulated the ouabain-sensitive 86Rb+ uptake in a time- and dose-dependent fashion; (2) this effect was abolished by addition of H-89 or Rp-cAMPS, two structurally different PKA inhibitors; and (3) this stimulation was not affected by inhibition of protein kinase C (PKC) by GF109203X. The stimulatory effect of db-cAMP on the hydrolytic activity of Na+,K+-ATPase was accounted for by an increased maximal ATPase rate (Vmax) without alteration of the efficiency of the pump, suggesting that cAMP-PKA pathway was implicated in membrane redistribution control. 3To test this hypothesis, we used two different approaches: (1) cell surface protein biotinylation and (2) subcellular fractionation. Both approaches confirmed that the cAMP-PKA pathway was implicated in membrane trafficking regulation. The stimulation of Na+,K+-ATPase activity by db-cAMP was associated with an increase (+40 %) in Na+,K+-ATPase units expressed at the cell surface which was assessed by Western blotting after streptavidin precipitation of biotinylated cell surface proteins. Subcellular fractionation confirmed the increased expression in pump units at the cell surface which was accompanied by a decrease (-30 %) in pump units located in the subcellular fraction corresponding to early endosomes. 4In conclusion, PKA stimulates Na+,K+-ATPase activity, at least in part, by increasing the number of Na+-K+ pumps in the plasma membrane in Proximal Convoluted Tubule cells.
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modulation of na k atpase activity by a tyrosine phosphorylation process in rat Proximal Convoluted Tubule
The Journal of Physiology, 1997Co-Authors: Eric Feraille, Maria Luisa Carranza, Martine Rousselot, Herve FavreAbstract:1. In the rat kidney Proximal Convoluted Tubule, epidermal growth factor and insulin have been reported to stimulate Na+ reabsorption. Because most of the effects of these growth factors are mediated by a process of tyrosine phosphorylation and Na+,K(+)-ATPase drives Na+ reabsorption, the influence of tyrosine kinases and tyrosine phosphatases on Na+,K(+)-ATPase activity located in the Proximal Convoluted Tubule was evaluated. 2. Activation of receptor tyrosine kinases by epidermal growth factor and insulin stimulated ouabain-sensitive 86Rb+ uptake. The effects of epidermal growth factor and insulin were prevented by genistein, a tyrosine kinase inhibitor, but were unaffected by GF109203X, a protein kinase C inhibitor. 3. Inhibition of tyrosine phosphatases by orthovanadate (10(-7) and 10(-6)M) mimicked the effects of activation of receptor tyrosine kinases: stimulation of the ouabain-sensitive 86Rb+ uptake and of the hydrolytic activity of Na+,K(+)-ATPase under rate-limiting Na+ concentration, and absence of modification of the maximal activity (Vmax) of the enzyme. The effects of orthovanadate and insulin on the ouabain-sensitive 86Rb+ uptake were not additive. 4. The present results show that both activation of receptor tyrosine kinases and inhibition of tyrosine phosphatases stimulate the Na+,K(+)-ATPase activity through a common mechanism. Thus, a tyrosine phosphorylation process directly controls the Na+,K(+)-ATPase activity and contributes to the physiological control of water and solute reabsorption in the Proximal Convoluted Tubule.
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Modulation of Na+,K(+)-ATPase activity by a tyrosine phosphorylation process in rat Proximal Convoluted Tubule.
The Journal of Physiology, 1997Co-Authors: Eric Feraille, Maria Luisa Carranza, Martine Rousselot, Herve FavreAbstract:1. In the rat kidney Proximal Convoluted Tubule, epidermal growth factor and insulin have been reported to stimulate Na+ reabsorption. Because most of the effects of these growth factors are mediated by a process of tyrosine phosphorylation and Na+,K(+)-ATPase drives Na+ reabsorption, the influence of tyrosine kinases and tyrosine phosphatases on Na+,K(+)-ATPase activity located in the Proximal Convoluted Tubule was evaluated. 2. Activation of receptor tyrosine kinases by epidermal growth factor and insulin stimulated ouabain-sensitive 86Rb+ uptake. The effects of epidermal growth factor and insulin were prevented by genistein, a tyrosine kinase inhibitor, but were unaffected by GF109203X, a protein kinase C inhibitor. 3. Inhibition of tyrosine phosphatases by orthovanadate (10(-7) and 10(-6)M) mimicked the effects of activation of receptor tyrosine kinases: stimulation of the ouabain-sensitive 86Rb+ uptake and of the hydrolytic activity of Na+,K(+)-ATPase under rate-limiting Na+ concentration, and absence of modification of the maximal activity (Vmax) of the enzyme. The effects of orthovanadate and insulin on the ouabain-sensitive 86Rb+ uptake were not additive. 4. The present results show that both activation of receptor tyrosine kinases and inhibition of tyrosine phosphatases stimulate the Na+,K(+)-ATPase activity through a common mechanism. Thus, a tyrosine phosphorylation process directly controls the Na+,K(+)-ATPase activity and contributes to the physiological control of water and solute reabsorption in the Proximal Convoluted Tubule.
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insulin enhances sodium sensitivity of na k atpase in isolated rat Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1994Co-Authors: Eric Feraille, Maria Luisa Carranza, Martine Rousselot, Herve FavreAbstract:Insulin has been shown to stimulate the rate of ouabain-sensitive 86Rb influx in the isolated rat Proximal Convoluted Tubule (PCT). To study the mechanism of this activation of Na-K-adenosinetriphosphatase (Na-K-ATPase), we determined the actions of insulin on 1) the maximal activity (Vmax) of Na-K-ATPase hydrolytic activity; 2) the maximal rate of ouabain-sensitive 86Rb influx (after intracellular Na loading); 3) the rate of ouabain-sensitive 86Rb influx under conditions where intracellular Na concentration is rate limiting, either in the presence or in the absence of 5 x 10(-4) M amiloride and/or low extracellular Na concentration (3 mM); and 4) the Na sensitivity of the Na-K-ATPase hydrolytic activity. The maximal rates of Na-K-ATPase hydrolytic activity and of ouabain-sensitive 86Rb uptake were unchanged by insulin. In contrast, we confirmed that insulin enhanced 86Rb uptake (in peq.mm-1.min-1) in the absence of inhibitor of the Na/H exchanger [18.2 +/- 1.7 to 24.1 +/- 1.3 (SE), P < 0.03] and, in addi...
Raynald Laprade - One of the best experts on this subject based on the ideXlab platform.
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inhibition of basolateral potassium conductance by taurine in the Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1996Co-Authors: Sylvie Breton, Fouzia Belachgar, Mireille Marsolais, Jeanyves Lapointe, Raynald LapradeAbstract:The effect of taurine on the electrophysiological properties of the basolateral membrane of the rabbit Proximal Convoluted Tubule was examined. Short-duration isosmotic pulses of 40 mM taurine in t...
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hypotonicity increases basolateral taurine permeability in rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1995Co-Authors: Sylvie Breton, Mireille Marsolais, Raynald LapradeAbstract:The permeabilities of the basolateral membrane of rabbit Proximal Convoluted Tubule (PCT) to taurine (PTau) and glucose (PGlc) were estimated under control and hypotonic conditions using the initial rate of increase in cellular volume (CV) induced on isotonic replacement of 40 mM mannitol by one or the other of these substrates. Under control conditions, addition of taurine led to an increase in CV at an initial rate of 7.1 +/- 1.7%/min, leading to a cell swelling of 30.2 +/- 4.8% after 5 min (n = 6). Addition of glucose led to an increase in CV at an initial rate of 30.0 +/- 3.8%/min, leading to a cell swelling of 25.7 +/- 3.1% after 5 min (n = 7). After a period of recovery of 5 min in the absence of taurine or glucose, a 40 mosmol/kg hypotonic shock induced a cell swelling of 14.2 +/- 1.3 and 16.1 +/- 5.2%, respectively, followed by an almost complete volume regulatory decrease after 5 min. At that time, addition of taurine under continuous hypotonicity induced an increase in CV at an initial rate 2.57...
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camp stimulates Proximal Convoluted Tubule na k atpase activity
American Journal of Physiology-renal Physiology, 1994Co-Authors: Sylvie Breton, J S Beck, Raynald LapradeAbstract:The effect of adenosine 3',5'-cyclic monophosphate (cAMP) was examined on the electrophysiological properties of nonperfused Proximal Convoluted Tubule in vitro. In 5 mM bath K+, the basolateral membrane potential (Vbl) was -66 +/- 1 mV (n = 26). Low bath K+ (0.1 mM) led to a transient hyperpolarization of Vbl followed by a sustained decrease to reach -48.6 +/- 5.0 mV. Return to 5 mM bath K+ produced a rapid and transient Vbl hyperpolarization of 24.6 +/- 1.4 mV (n = 5). This hyperpolarization was completely blocked by 100 microM strophanthidin (n = 4), demonstrating that the hyperpolarization was caused by reactivation of the Na(+)-K(+)-adenosinetriphosphatase (ATPase). Addition of 1 microM forskolin (forsk) + 100 microM 8-(4-chlorophenylthio)-cAMP (cp-cAMP) significantly increased this hyperpolarization to 30.8 +/- 10 mV (P < 0.005, n = 5). In a separate series of experiments, addition of 1 microM forsk + 100 microM 3-isobutyl-1-methylxanthine increased this hyperpolarization from 21.7 +/- 2.8 to 27.1 +/- 1.6 mV (P < 0.05, n = 5), which excludes any nonspecific effect of cp-cAMP. Forsk + cp-cAMP decreased the apparent partial conductance to Cl- (tCl) from 0.049 +/- 0.003 to 0.031 +/- 0.007 (P < 0.06, n = 6), decreased that to K+ (tK) from 0.56 +/- 0.05 to 0.43 +/- 0.03 (P < 0.05, n = 6), slightly decreased that mediated by the Na-HCO3 cotransporter (tNaHCO3) from 0.26 +/- 0.03 to 0.21 +/- 0.05, and had no effect on the absolute conductance mediated by the Na-HCO3 cotransporter. Forsk + cp-cAMP had no effect on tK when determined using bath K+ steps from 15 to 45 mM (tK = 0.84 +/- 0.02, n = 5) instead of K+ steps from 5 to 15 mM as previously done, and did not affect the value of tK measured in the presence of strophanthidin (tK = 0.41 +/- 0.03, n = 5). These results demonstrate that the decrease of tK by forsk + cp-cAMP observed using K+ steps from 5 to 15 mM is due to modulation by these agents of the stimulated hyperpolarizing Na(+)-K(+)-ATPase current produced by the bath K+ steps. Consequently, the increased Vbl initial recovery from low bath potassium observed when intracellular cAMP is increased could not be the result of modulation of passive basolateral membrane properties and represents a stimulation of the pump current. The present work thus demonstrates that the Na(+)-K(+)-ATPase is stimulated by cAMP.
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na pump inhibition downregulates an atp sensitive k channel in rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1993Co-Authors: A M Hurst, J S Beck, Raynald Laprade, Jeanyves LapointeAbstract:In several epithelial and nonepithelial tissues a functional link between the basolateral Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) and a basolateral K+ conductance has been established. However, the nature of this link is unclear. We have previously identified a K+ channel on the basolateral membrane of the Proximal Convoluted Tubule perfused in vitro, the activity of which is increased by stimulation of Na+ transport [J. S. Beck, A. M. Hurst, J.-Y. Lapointe, and R. Laprade. Am. J. Physiol. 264 (Renal Fluid Electrolyte Physiol. 33): F496-F501, 1993]. In the present study we investigate whether basolateral membrane K+ channel activity is tightly coupled to Na(+)-K(+)-ATPase activity. In cell-attached patches (150 mM K+ pipette), following stimulation of channel activity by addition of Na(+)-cotransported solutes to the Tubule lumen, mean channel open probability (NPo) was reduced from 0.35 +/- 0.09 to 0.14 +/- 0.06 (n = 7, P < 0.05) by blocking the Na(+)-K(+)-ATPase with 100 microM strophanthidin. In excised patches the channel was reversibly blocked by 2 mM ATP from the cytosolic face of the patch, such that NPo fell to 20.1 +/- 7.0% (n = 5, P < 0.001) of control and recovered to 52.2 +/- 11.2% (n = 5, P < 0.05) after washout of ATP. Diazoxide, a putative opener of ATP-sensitive K+ channels, when added to the bathing solution of an unstimulated Tubule (microperfused in the absence of Na(+)-cotransported solutes), increased NPo from 0.046 +/- 0.035 to 0.44 +/- 0.2 (n = 6, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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evidence against a proton pump in rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1993Co-Authors: J S Beck, Raynald LapradeAbstract:: H+/OH- transport in the absence of bicarbonate was studied in the rabbit Proximal Convoluted Tubule (PCT) perfused in vitro using measurements of membrane potential and intracellular pH (pHi). Blockade of apical Na/H exchange led to a cell acidification of 0.64 +/- 0.1 pH units from a control pHi of 7.27 +/- 0.04. A bafilomycin-insensitive recovery of pHi of 0.05 +/- 0.02 pH units occurred, but pHi did not exceed electrochemical equilibrium. A larger, sustained acidification of 0.87 +/- 0.07 from an initial control pHi of 7.25 +/- 0.05 induced by bilateral Na removal left pHi substantially below electrochemical equilibrium. These results suggest the absence of Na-independent active proton extrusion. We also examined the possibility that a passive electrogenic proton leak may exist. The removal of luminal glucose and alanine led to a basolateral membrane hyperpolarization of 31.3 +/- 0.5 mV, which was associated with a cell acidification of 0.15 +/- 0.02 pH units. These responses were reversed by addition of luminal glucose and alanine but not by depolarization by basolateral barium, suggesting that luminal glucose and alanine effects on pHi were due to changes other than cell potential. We conclude that, in the absence of bicarbonate, all active proton extrusion in the rabbit PCT is dependent on active Na transport and that a proton leak is negligible.
Sylvie Breton - One of the best experts on this subject based on the ideXlab platform.
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inhibition of basolateral potassium conductance by taurine in the Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1996Co-Authors: Sylvie Breton, Fouzia Belachgar, Mireille Marsolais, Jeanyves Lapointe, Raynald LapradeAbstract:The effect of taurine on the electrophysiological properties of the basolateral membrane of the rabbit Proximal Convoluted Tubule was examined. Short-duration isosmotic pulses of 40 mM taurine in t...
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hypotonicity increases basolateral taurine permeability in rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1995Co-Authors: Sylvie Breton, Mireille Marsolais, Raynald LapradeAbstract:The permeabilities of the basolateral membrane of rabbit Proximal Convoluted Tubule (PCT) to taurine (PTau) and glucose (PGlc) were estimated under control and hypotonic conditions using the initial rate of increase in cellular volume (CV) induced on isotonic replacement of 40 mM mannitol by one or the other of these substrates. Under control conditions, addition of taurine led to an increase in CV at an initial rate of 7.1 +/- 1.7%/min, leading to a cell swelling of 30.2 +/- 4.8% after 5 min (n = 6). Addition of glucose led to an increase in CV at an initial rate of 30.0 +/- 3.8%/min, leading to a cell swelling of 25.7 +/- 3.1% after 5 min (n = 7). After a period of recovery of 5 min in the absence of taurine or glucose, a 40 mosmol/kg hypotonic shock induced a cell swelling of 14.2 +/- 1.3 and 16.1 +/- 5.2%, respectively, followed by an almost complete volume regulatory decrease after 5 min. At that time, addition of taurine under continuous hypotonicity induced an increase in CV at an initial rate 2.57...
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camp stimulates Proximal Convoluted Tubule na k atpase activity
American Journal of Physiology-renal Physiology, 1994Co-Authors: Sylvie Breton, J S Beck, Raynald LapradeAbstract:The effect of adenosine 3',5'-cyclic monophosphate (cAMP) was examined on the electrophysiological properties of nonperfused Proximal Convoluted Tubule in vitro. In 5 mM bath K+, the basolateral membrane potential (Vbl) was -66 +/- 1 mV (n = 26). Low bath K+ (0.1 mM) led to a transient hyperpolarization of Vbl followed by a sustained decrease to reach -48.6 +/- 5.0 mV. Return to 5 mM bath K+ produced a rapid and transient Vbl hyperpolarization of 24.6 +/- 1.4 mV (n = 5). This hyperpolarization was completely blocked by 100 microM strophanthidin (n = 4), demonstrating that the hyperpolarization was caused by reactivation of the Na(+)-K(+)-adenosinetriphosphatase (ATPase). Addition of 1 microM forskolin (forsk) + 100 microM 8-(4-chlorophenylthio)-cAMP (cp-cAMP) significantly increased this hyperpolarization to 30.8 +/- 10 mV (P < 0.005, n = 5). In a separate series of experiments, addition of 1 microM forsk + 100 microM 3-isobutyl-1-methylxanthine increased this hyperpolarization from 21.7 +/- 2.8 to 27.1 +/- 1.6 mV (P < 0.05, n = 5), which excludes any nonspecific effect of cp-cAMP. Forsk + cp-cAMP decreased the apparent partial conductance to Cl- (tCl) from 0.049 +/- 0.003 to 0.031 +/- 0.007 (P < 0.06, n = 6), decreased that to K+ (tK) from 0.56 +/- 0.05 to 0.43 +/- 0.03 (P < 0.05, n = 6), slightly decreased that mediated by the Na-HCO3 cotransporter (tNaHCO3) from 0.26 +/- 0.03 to 0.21 +/- 0.05, and had no effect on the absolute conductance mediated by the Na-HCO3 cotransporter. Forsk + cp-cAMP had no effect on tK when determined using bath K+ steps from 15 to 45 mM (tK = 0.84 +/- 0.02, n = 5) instead of K+ steps from 5 to 15 mM as previously done, and did not affect the value of tK measured in the presence of strophanthidin (tK = 0.41 +/- 0.03, n = 5). These results demonstrate that the decrease of tK by forsk + cp-cAMP observed using K+ steps from 5 to 15 mM is due to modulation by these agents of the stimulated hyperpolarizing Na(+)-K(+)-ATPase current produced by the bath K+ steps. Consequently, the increased Vbl initial recovery from low bath potassium observed when intracellular cAMP is increased could not be the result of modulation of passive basolateral membrane properties and represents a stimulation of the pump current. The present work thus demonstrates that the Na(+)-K(+)-ATPase is stimulated by cAMP.
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relationship between sodium transport and intracellular atp in isolated perfused rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1991Co-Authors: J S Beck, Sylvie Breton, R Laprade, H Mairbaurl, G GiebischAbstract:: The effect of alterations in sodium transport on cell ATP content and pH in the isolated perfused Proximal Convoluted Tubule (PCT) of the rabbit was examined. Stimulating sodium transport by the addition of luminal glucose and alanine decreased cell ATP from 4.44 +/- 0.93 to 2.69 +/- 0.62 mM (n = 4), increased intracellular pH by 0.13 +/- 0.02 (n = 7), and increased cell volume by 0.10 +/- 0.02 nl/mm (n = 4). Blocking the sodium pump with 10(-4) M strophanthidin in Tubules in which sodium transport had been stimulated increased cell ATP from 2.04 +/- 0.24 to 2.42 +/- 0.32 mM (n = 6). In parallel experiments the same dose of strophanthidin depolarized the basolateral membrane from -52.6 +/- 1.9 to -6.4 +/- 1.6 mV, depolarized the transepithelial potential from -3.2 +/- 0.3 to -0.1 +/- 0.1 mV, and reduced the basolateral membrane potassium transference number from 0.47 to 0.26 indicating a reduction in basolateral potassium conductance. Since strophanthidin caused a cell alkalinization of 0.15 +/- 0.03, this latter effect cannot be due to changes of intracellular pH. Strophanthidin caused no change in cell volume over the period studied, suggesting that stretch-activated potassium channels are not involved either. Instead, potassium conductance inhibition may be the result of the closure of ATP-sensitive potassium channels. These same channels might thus be partly responsible for the increase in potassium conductance commonly observed during stimulation of sodium transport.
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volume regulation and intracellular calcium in the rabbit Proximal Convoluted Tubule
American Journal of Physiology-renal Physiology, 1991Co-Authors: J S Beck, Sylvie Breton, R Laprade, G GiebischAbstract:The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused Proximal Convoluted Tubule of the r...
