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Per Hellstrand - One of the best experts on this subject based on the ideXlab platform.

  • nitric oxide relaxes rat tail artery smooth muscle by cyclic gmp independent decrease in calcium sensitivity of myofilaments
    Cell Calcium, 2004
    Co-Authors: Anatoly Soloviev, Vyacheslav Lehenkyi, S N Zelensky, Per Hellstrand
    Abstract:

    The effects of authentic nitric oxide (NO, 10(-6) M) and NO-donors such as sodium nitroprusside (SNP, 10(-5) M) and glyceryl trinitrate (GTN, 10(-4) M) on contractile force and free intracellular calcium level ([Ca2+],) were studied on precontracted with high potassium chloride (KCI, 70 mM) isolated rings of rat tail artery. The sensitivity of contractile myofilaments to Ca2+ was measured using chemically permeabilized (alpha-toxin, Beta-Escin, Triton X-100) vascular rings. [Ca2+](i) and contractile activity were measured simultaneously. The relationship of [Ca2+](i) and tension developed was studied in endothelium-denuded rings and controlled calcium response was evaluated in both endothelium-denuded and permeabilized vascular rings. Both authentic NO and NO-donors decreased [Ca2+](i) and high potassium-induced tension with a different time course. Inhibitor of soluble guanylyl cyclase (sGC) LY83583 (10(-5) M) did not affect SNP-induced relaxation whereas the other sGC inhibitor ODQ (10(-6) M) attenuated SNP-induced relaxation. Both inhibitors had no effect on NO- and SNP-induced reduction in [Ca2+](i). On the contrary, GTN induced neither relaxation nor decrease in [Ca2+](i) on application of both LY83583 and ODQ. Tail artery rings permeabilized with alpha-toxin, Beta-Escin, but not with Triton X-100 were relaxed by authentic NO and NO-donors, but to a less extent than non-permeabilized rings. Dithioerythritol (DTE, 5 x 10(-3) M) that maintains sulfhydryl (SH) groups in reduced state preventing their nitrosylation attenuated NO-induced relaxation in both non-permeabilized and permeabilized tail artery rings. The cyclic heptapeptide mycrocystin-LR (MC-LR) (10(-5) M), an inhibitor of type I and 2A phosphatases, induced sustained increase in tension of Beta-Escin permeabilized rings in low Ca2+ (10(-8) M) solution. The tension was not affected by authentic NO and SNP. We conclude that authentic NO and SNP relax rat tail artery smooth muscle (SM) in the presence of inhibitors of sGC via cyclic guanosine monophosphate (cGMP)- independent pathway, whereas relaxation induced by GTN is inhibited. The data demonstrate that cGMP-dependent pathway in vascular smooth muscle is ubiquitous, but not the only way of relaxation induced by NO. NO can modulate vascular tone directly by reducing sensitivity of contractile myofilaments to [Ca2+](i) and may involve activation of protein phosphatase(s). (C) 2004 Elsevier Ltd. All rights reserved. (Less)

  • Long-term effects of Ca(2+) on structure and contractility of vascular smooth muscle.
    The American journal of physiology, 1999
    Co-Authors: Anders Lindqvist, Ulf Malmqvist, Ina Nordström, Patrik Nordenfelt, Per Hellstrand
    Abstract:

    Culture of dispersed smooth muscle cells is known to cause rapid modulation from the contractile to the synthetic cellular phenotype. However, organ culture of smooth muscle tissue, with maintained extracellular matrix and cell-cell contacts, may facilitate maintenance of the contractile phenotype. To test the influence of culture conditions, structural, functional, and biochemical properties of rat tail arterial rings were investigated after culture. Rings were cultured for 4 days in the absence and presence of 10% FCS and then mounted for physiological experiments. Intracellular Ca(2+) concentration ([Ca(2+)](i)) after stimulation with norepinephrine was similar in rings cultured with and without FCS, whereas force development after FCS was decreased by >50%. The difference persisted after permeabilization with Beta-Escin. These effects were associated with the presence of vasoconstrictors in FCS and were dissociated from its growth-stimulatory action. FCS treatment increased lactate production but did not affect ATP, ADP, or AMP contents. The contents of actin and myosin were decreased by culture but similar for all culture conditions. There was no effect of FCS on calponin contents or myosin SM1/SM2 isoform composition, nor was there any appearance of nonmuscle myosin. FCS-stimulated rings showed evidence of cell degeneration not found after culture without FCS or with FCS + verapamil (1 microM) to lower [Ca(2+)](i). The decreased force-generating ability after culture with FCS is thus associated with increased [Ca(2+)](i) during culture and not primarily caused by growth-associated modulation of cells from the contractile to the synthetic phenotype.

  • Contractile effects of polycations in permeabilized smooth muscle
    Journal of muscle research and cell motility, 1998
    Co-Authors: Karl Swärd, Karl Dreja, Per Hellstrand
    Abstract:

    The polycations spermine, neomycin and polylysine potentiated Ca(2+)-activated force in Beta-Escin permeabilized guinea-pig ileum strips. The effect was inhibited by the calmodulin antagonists trifluoperazine, mastoparan and W13. Potentiation was slow or absent in chi-toxin permeabilized strips, indicating dependence on penetration of the polycations into cells. The effects of spermine and neomycin were maintained after extensive permeabilization by Beta-Escin, which eliminated the contractile effect of GTPgammaS. Replacement of ATP by CTP, which is not a substrate for myosin light chain kinase, inhibited contractile potentiation. Potentiation of Ca(2+)-activated contractions was associated with increased phosphorylation of the myosin regulatory light chains (LC20). A contractile effect of polylysine and neomycin was also seen in Ca(2+)-free medium and after partial LC20 thiophosphorylation, indicating that phosphorylation-independent processes may contribute to the response. Although spermine does not cause contraction in Ca(2+)-free medium at physiological [MgATP], it did so when [MgATP] was lowered to 40 micron. Similar to high-[Mg2+], the rate of contraction on addition of ATP to strips incubated with microcystin-LR in inhibit phosphatase activity was increased by the polycations, but only at [Ca2+] < 0.3 micron. The results suggest that polycations increase Ca(2+)-activated force by inhibiting myosin phosphatase activity, thereby increasing myosin LC20 phosphorylation. However, additional activation mechanisms, evident at low [Ca2+] and at low [ATP] and possibly involving direct activation of myosin, contribute to their effect.

  • Polyamines inhibit myosin phosphatase and increase LC20 phosphorylation and force in smooth muscle
    American Journal of Physiology, 1995
    Co-Authors: Karl Swärd, M D Pato, Bengt-olof Nilsson, Ina Nordström, Per Hellstrand
    Abstract:

    The increase in Ca(2+)-activated force caused by polyamines in Beta-Escin-permeabilized guinda pig ileum is shown to be associated with increased myosin 20-kDa light chain (LC20) phosphorylation and shortening velocity. Myosin LC20 dephosphorylation with arrested kinase activity was slower in the presence of 1 mM spermine. Smooth muscle phosphatases (SMP-I, -II, -III, and -IV) isolated from turkey gizzard are all active against phosphorylated LC20, but only SMP-III and -IV dephosphorylate heavy meromyosin (HMM). Spermine inhibited SMP-III activity toward LC20 but stimulated HMM dephosphorylation, whereas SMP-IV was inhibited with both substrates. In contrast, SMP-I and -II were stimulated by spermine. The relative effects of different polyamines correlated with an increasing number of positive charges. Spermine did not affect binding of SMP-IV to myosin and did not dissociate any of the subunits of the enzyme. Incubation of permeabilized strips with SMP-IV resulted in attenuated responses to Ca2+, an effect that was opposed by spermine and abolished by microcystin-LR. We conclude that spermine selectively inhibits myosin phosphatase activity and suggest that polyamines function as endogenous myosin phosphatase inhibitors.

  • Differential actions of exogenous and intracellular spermine on contractile activity in smooth muscle of rat portal vein
    Acta physiologica Scandinavica, 1995
    Co-Authors: Bengt-olof Nilsson, Ina Nordström, Maria F. Gomez, R Santiago Carrilho, Per Hellstrand
    Abstract:

    Effects of the naturally occurring polyamine spermine on electrical and contractile properties of the rat portal vein were studied. 1 mM spermine nearly abolished spike activity and spontaneous contractions and decreased the intracellular Ca2+ concentration ([Ca2+]i). The phasic force responses to 0.1 and 1 microM phenylephrine were partially inhibited, but not the sustain plateau contraction caused by 5 microM phenylephrine. The Ca(2+)-force relation in high-K+ (128 mM)-depolarized veins was shifted to the right, EC50 for Ca2+ increasing from 0.50 +/- 0.03 mM (control, n = 8) to 0.65 +/- 0.06 and to 0.94 +/- 0.03 at 1 (n = 4) and 10 (n = 3) mM spermine, respectively. However, at a Ca2+ concentration of 2.5 mM, giving maximal force, there was no effect of spermine (1 mM) on either force or [Ca2+]i. Whereas extracellular spermine thus reduced contractile activity at moderate levels of stimulation, increased intracellular concentration of spermine potentiated the force response to Ca2+. Intracellular loading of spermine by reversible permeabilization increased its concentration by 2-3 times. The spontaneous activity and response to phenylephrine were unchanged. However, the Ca(2+)-force relation of depolarized veins was shifted to the left, EC50 decreasing from 0.51 +/- 0.04 mM in controls (n = 7) to 0.36 +/- 0.02 mM in the loaded veins (n = 9). Spermine increased Ca(2+)-activated force in portal veins permeabilized with Beta-Escin. The degree of potentiation was consistent with observed effects in spermine-loaded intact veins. The results suggest that spermine at physiological intracellular concentration may contribute to the determination of Ca2+ sensitivity in vascular smooth muscle cells.

Takeo Itoh - One of the best experts on this subject based on the ideXlab platform.

  • Mechanism underlying H2O2-induced inhibition of acetylcholine-induced contraction in rabbit tracheal smooth muscle.
    European journal of pharmacology, 2006
    Co-Authors: Michihiro Saito, Yoshimasa Watanabe, Takeo Itoh
    Abstract:

    The mechanism underlying the inhibition by H2O2 of acetylcholine-induced contraction was investigated in epithelium-denuded strips of rabbit trachea. Acetylcholine (10 microM) generated a phasic, followed by a tonic increase in both the intracellular Ca2+ concentration ([Ca2+]i) and force. Although the acetylcholine-induced tonic contraction was around 9 times the high K+ (80 mM)-induced one, the two stimulants induced similar [Ca2+]i increases (around 0.2 microM), indicating that acetylcholine generates tonic contraction via increases in both [Ca2+]i and myofilament Ca2+-sensitivity. H2O2 (30 microM) (a) enhanced the acetylcholine-induced tonic (not phasic) increase in [Ca2+]i but attenuated both phases of the acetylcholine-induced contraction and (b) enhanced the high K+-induced increase in [Ca2+]i but did not modify the high K+-induced contraction. In Beta-Escin-skinned strips, application of acetylcholine in the presence of GTP enhanced the contraction induced by 0.3 microM Ca2+ so that its amplitude became similar to that induced by 1 microM Ca2+. H2O2 (30 microM) attenuated the contraction induced by 0.3 microM Ca2+ (alone or in the presence of acetylcholine) but not those induced by higher concentrations of Ca2+ alone (0.5 microM and 1 microM). These results indicate that H2O2 acts directly on contractile proteins in rabbit tracheal smooth muscle to inhibit the contraction induced by low concentrations of Ca2+ (

  • Angiotensin II-induced modulation of endothelium-dependent relaxation in rabbit mesenteric resistance arteries.
    The Journal of physiology, 2003
    Co-Authors: Takeo Itoh, Junko Kajikuri, Toyohiro Tada, Yoshikatsu Suzuki, Yoshio Mabuchi
    Abstract:

    The role of local endogenous angiotensin II (Ang II) in endothelial function in resistance arteries was investigated using rabbit mesenteric resistance arteries. First, the presence of immunoreactive Ang II together with Ang II type-1 receptor (AT1R) and angiotensin converting enzyme (ACE) was confirmed in these arteries. In endothelium-intact strips, the AT1R-blocker olmesartan (1 microM) and the ACE-inhibitor temocaprilat (1 microM) each enhanced the ACh (0.03 microM)-induced relaxation during the contraction induced by noradrenaline (NA, 10 microM). Similar effects were obtained using CV-11974 (another AT1R blocker) and enalaprilat (another ACE inhibitor). The nitric-oxide-synthase inhibitor NG-nitro-L-arginine (L-NNA) abolished the above effect of olmesartan. In endothelium-denuded strips, olmesartan enhanced the relaxation induced by the NO donor NOC-7 (10 nM). Olmesartan had no effect on cGMP production (1) in endothelium-intact strips (in the absence or presence of ACh) or (2) in endothelium-denuded strips (in the absence or presence of NOC-7). In Beta-Escin-skinned strips, 8-bromoguanosine 3',5' cyclic monophosphate (8-Br-cGMP, 0.01-1 microM) concentration dependently inhibited the contractions induced (a) by 0.3 microM Ca2+ in the presence of NA+GTP and (b) by 0.2 microM Ca2++GTPgammaS. Olmesartan significantly enhanced, while Ang II (0.1 nM) significantly inhibited, the 8-Br-cGMP-induced relaxation. We propose the novel hypothesis that in these arteries, Ang II localized within smooth muscle cells activates AT1Rs and inhibits ACh-induced, endothelium-dependent relaxation at least partly by inhibiting the action of cGMP on these cells.

  • Effect of a peptide inhibitor of protein kinase C on G‐protein‐mediated increase in myofilament Ca2+‐sensitivity in rabbit arterial skinned muscle
    British journal of pharmacology, 1994
    Co-Authors: Takeo Itoh, Akito Suzuki, Yoshimasa Watanabe
    Abstract:

    1. To investigate the role of protein kinase C in the increase mediated by guanosine 5'-triphosphate (GTP)-binding proteins (G-proteins) in the sensitivity of the contractile proteins to Ca2+ in vascular smooth muscle, the effect of a novel peptide inhibitor of protein kinase C (PKC19-36) on Ca(2+)-induced contraction and myosin light chain (MLC) phosphorylation was studied in the presence and absence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) in Beta-Escin-skinned smooth muscle strips of rabbit mesenteric artery. For comparison, the effects were also observed of PKC19-36 on the action of phorbol 12,13-dibutylate (PDBu, an activator of PKC) on the two Ca(2+)-induced responses. 2. In Beta-Escin-skinned strips treated with ionomycin, Ca2+ (0.1-3 microM) concentration-dependently produced contraction in parallel with an increase in MLC-phosphorylation. GTP gamma S (10 microM) and PDBu (0.1 microM) each shifted both the Ca(2+)-force and Ca(2+)-MLC-phosphorylation relationships to the left without a significant change in either maximum response. The relationship between force and MLC-phosphorylation was not modified by either GTP gamma S or PDBu, indicating that the sensitivity of MLC-phosphorylation to Ca2+ is enhanced by both GTP gamma S and PDBu. 3. PKC19-36 itself modified neither the contraction nor MLC-phosphorylation induced by Ca2+ but it did block the PDBu-induced enhancement of these two Ca(2+)-induced responses. By contrast, PKC19-36 did not modify the GTP gamma S-induced enhancement of the two Ca(2+)-induced responses. Guanosine 5'-O-(2-thiodiphosphate) (GDP Beta S) attenuated the GTP gamma S-induced enhancement of the Ca2+-induced contraction.4. These results suggest that GTP gamma S increases Ca2+-induced MLC-phosphorylation through the activation of a PKC-independent mechanism and thus causes an increase in the sensitivity of the contractile proteins to Ca2+ in Beta-Escin-skinned smooth muscle of rabbit mesenteric artery.

  • Characteristic features of noradrenaline‐induced Ca2+ mobilization and tension in arterial smooth muscle of the rabbit.
    The Journal of physiology, 1992
    Co-Authors: Takeo Itoh, Junko Kajikuri, Hirosi Kuriyama
    Abstract:

    1. Effects of noradrenaline (NAd) on changes in cellular Ca2+ concentration ([Ca2+]i) and tension were investigated, and these effects were compared with those evoked by 128 mM K+ or caffeine in intact smooth muscle strips or by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) or caffeine in Beta-Escin-treated chemically skinned smooth muscle strips of the rabbit mesenteric artery. 2. In physiological solution containing 2.6 mM Ca2+, application of 128 mM K+ or 10 microM NAd produced a phasic, followed by a tonic increase in [Ca2+]i and tension. NAd (10 microM) produced a larger tonic tension than did 128 mM K+ but a smaller increase in [Ca2+]i. When the [Ca2+]i-tension relationship was observed in ionomycin- and 128 mM K(+)-treated muscle strips, 10 microM NAs shifted the relationship to the left and enhanced the maximum amplitude of contraction. These results suggest that NAd increases the sensitivity of contractile proteins to Ca2+ in smooth muscle of the rabbit mesenteric artery. 3. Noradrenaline (10 microM) or caffeine (10 mM), but not 128 mM K+, produced a phasic increase in both [Ca2+]i and tension in Ca(2+)-free solution containing 2 mM EGTA. When 10 mM caffeine had been applied in Ca(2+)-free solution, subsequent application of 10 microM NAd did not increase [Ca2+]i. By contrast, when 10 microM NAd had been applied in Ca(2+)-free solution, subsequent application of 10 mM caffeine still increased [Ca2+]i. Ryanodine (50 microM) abolished the increase in [Ca2+]i induced by 10 mM caffeine or 10 microM NAd in intact and in skinned smooth muscle strips. These results suggest that NAd releases Ca2+ from the ryanodine-sensitive Ca2+ storage sites. 4. Noradrenaline (10 microM) synthesized Ins(1,4,5)P3 in Ca(2+)-free solution in intact smooth muscle strips. Following application of 10 microM NAd, a relatively long time lag (around 1 s) was always observed before the initiation of the increase in [Ca2+]i whether in the presence or absence of Ca2+. The maximum rate of rise of [Ca2+]i induced by 10 mM caffeine was much larger than that induced by 10 microM NAd in Ca(2+)-containing or Ca(2+)-free solution (containing 2 mM EGTA). Both [Ca2+]i and tension reached their peak in a shorter time with caffeine (10 mM) than with 10 microM NAd. In Beta-Escin-treated skinned smooth muscle strips, 20 microM Ins(1,4,5)P3 10 mM caffeine or 10 microM NAd increased Ca2+ in Ca(2+)-free solution following brief application of 0.3 microM Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Gabriele Pfitzer - One of the best experts on this subject based on the ideXlab platform.

  • Sustained norepinephrine contraction in the rat portal vein is lost when Ca(2+) is replaced with Sr(2+).
    American journal of physiology. Cell physiology, 2002
    Co-Authors: Johan Bonnevier, Gabriele Pfitzer, Ulf Malmqvist, Dagmar Sonntag, Mechthild Schroeter, Holger Nilsson, Anders Arner
    Abstract:

    Agonist-induced activation of smooth muscle involves a rise in intracellular Ca(2+) concentration and sensitization of myosin light chain phosphorylation to Ca(2+). Sr(2+) can enter through Ca(2+) channels, be sequestered and released from sarcoplasmic reticulum, and replace Ca(2+) in activation of myosin light chain phosphorylation. Sr(2+) cannot replace Ca(2+) in facilitation of agonist-activated Ca(2+)-dependent nonselective cation channels. It is not known whether Sr(2+) can replace Ca(2+) in small G protein-mediated sensitization of phosphorylation. To explore mechanisms involved in alpha-receptor-activated contractions in smooth muscle, effects of replacing Ca(2+) with Sr(2+) were examined in rat portal vein. Norepinephrine (NE) at >3.0 x 10(-7) M in the presence of Ca(2+) resulted in a strong sustained contraction, whereas this sustained component was absent in the presence of Sr(2+); only the amplitude of phasic contractions increased. Pretreatment with low (approximately 0.05 mM) free Ca(2+) followed by 2.5 mM Sr(2+) resulted in a sustained component of the NE response. In Beta-Escin-permeabilized preparations, phenylephrine in the presence of GTP or guanosine 5'-O-(3-thiotriphosphate) alone induced sensitization to Sr(2+). In conclusion, a Ca(2+)-regulated membrane/channel process is required for the sustained component of NE responses in rat portal vein. Sensitization alone is not responsible for the sustained phase of the NE contraction.

  • Augmented agonist-induced Ca(2+)-sensitization of coronary artery contraction in genetically hypertensive rats. Evidence for altered signal transduction in the coronary smooth muscle cells.
    The Journal of clinical investigation, 1994
    Co-Authors: S. Satoh, R Kreutz, C Wilm, D Ganten, Gabriele Pfitzer
    Abstract:

    Abstract The Ca2+ responsiveness of vascular smooth muscle myofilaments is not unique: it is increased during neuro-humoral activation and decreased during Beta-adrenergic stimulation. In this study we tested whether an augmented Ca2+ responsiveness of smooth muscle myofilaments may contribute to the increased coronary tone observed in hypertension using Beta-Escin-permeabilized coronary arteries from 3-mo-old stroke-prone spontaneously hypertensive rats (SHRSP) and their age matched normotensive reference strain (WKY rats). In intact coronary arteries, the response to 5-hydroxytryptamine (5-HT) but not to KCl was larger in SHRSP than in WKY rats. In Beta-Escin permeabilized coronary arteries in which the receptor effector coupling is still intact, 5-HT enhanced force at constant submaximal (Ca2+) (pCa 6.38) to a greater extent in SHRSP. The Ca2+ sensitizing effect of 5-HT was mimicked by GTP gamma S (0.01-10 microM); again this effect was larger in SHRSP. In the absence of 5-HT or GTP gamma S the Ca2+ force relation was similar in both groups. Forskolin induced relaxation at constant submaximal (Ca2+). This desensitizing effect was smaller in SHRSP than in WKY rats. In conclusion, this study shows that intracellular signalling pathways involved in modulating the Ca2+ responsiveness of coronary smooth muscle myofilaments are altered in the genetically hypertensive animals favoring a hypercontractile state in the coronary circulation.

  • tyrosine kinase inhibitors suppress agonist induced contraction in smooth muscle
    Biochemical and Biophysical Research Communications, 1993
    Co-Authors: J Disalvo, S. Satoh, A Steusloff, L Semenchuk, K Kolquist, Gabriele Pfitzer
    Abstract:

    Because tyrosine kinases participate in diverse signalling pathways, we suspected that these enzymes might also participate in regulation of signal transduction in smooth muscle. Therefore, we studied the effects of geldanomycin, tyrphostin, and genistein, three structurally unrelated tyrosine kinase inhibitors, on receptor-mediated and depolarization-mediated contraction in three different types of smooth muscle. Contraction elicited by stimulation of muscarinic receptors with carbachol, or by stimulation of alpha-adrenergic receptors with norepinephrine or phenylephrine were markedly (> 80%) and reversibly inhibited by tyrosine-kinase inhibitors. In contrast, only slight inhibition (20%) occurred in contractions elicited by K(+)-induced depolorization. Moreover, tyrphostin did not inhibit direct Ca(2+)-mediated activation of the contractile apparatus in preparations permeabilized with Beta-Escin. These results suggest the novel hypothesis that tyrosine kinases participate in regulation of signal transduction that is associated with receptor-mediated contraction of smooth muscle.

Roger Marthan - One of the best experts on this subject based on the ideXlab platform.

  • Signalling pathways involved in the contractile response to 5-HT in the human pulmonary artery
    The European respiratory journal, 2009
    Co-Authors: Lise Rodat-despoix, Eric Rousseau, Jean-pierre Savineau, Roger Marthan, V Aires, Thomas Ducret, Christelle Guibert
    Abstract:

    Serotonin (5-hydroxytryptamine; 5-HT) is a potent pulmonary vasoconstrictor and mitogenic agent whose plasma level is increased in pulmonary hypertensive patients. Thus, we explored the signalling pathways involved in the contractile response to 5-HT in human pulmonary arteries (HPAs). Intact and Beta-Escin permeabilised rings from HPAs mounted in an organ bath system were used to assess both tension and myofilament Ca(2+)-sensitisation. Microspectrofluorimetry was used for intracellular Ca(2+) recordings in cultured HPA smooth muscle cells. Voltage-operated Ca(2+) channel blockers (nitrendipine and nifedipine) partially reduced the contraction to 5-HT. Thapsigargin or cyclopiazonic acid (CPA), known to deplete sarcoplasmic reticulum Ca(2+) stores, also partially inhibited the contraction, whereas removal of extracellular Ca(2+) under these conditions further inhibited the contraction. Changing from Ca(2+)-free to Ca(2+) containing solution, in the presence of nitrendipine and CPA, a protocol known to stimulate store-operated Ca(2+) channels, induced HPA contractions that were blocked by nickel. Nickel or gadolinium also reduced the contraction to 5-HT. Finally, 5-HT increased intracellular Ca(2+) responses in cultured HPA smooth muscle cells and myofilament Ca(2+)-sensitisation in HPA rings. Collectively, these results indicate that voltage-operated and voltage-independent Ca(2+) channels, as well as Ca(2+) release and myofilament Ca(2+)-sensitisation, participate in 5-HT-induced contraction in HPAs.

  • Activation properties of chemically skinned fibres from human isolated bronchial smooth muscle.
    The Journal of physiology, 1994
    Co-Authors: Jean-pierre Savineau, Roger Marthan
    Abstract:

    1. The contractile activation properties of human isolated bronchial smooth muscle were investigated using chemically (Beta-Escin) skinned strips. 2. Concentration-dependent contractions were induced by free ion concentrations of Ca2+ (0.5-3 microM), Sr2+ (2-200 microM) and Ba2+ (50-1000 microM). The resulting -log[cation]-tension relationships were fitted by sigmoidal curves with EC50 values (cation concentration required to produce half-maximal tension) and co-operativity factors (Hill coefficient, nH) of, respectively, 0.25 microM and 3.4 for Ca2+, 12 microM and 2.64 for Sr2+ and 100 microM and 1.73 for Ba2+. Maximal responses to Sr2+ and Ba2+ were 125.5 +/- 15.4 and 96 +/- 8.1% (n = 5) respectively of the maximum tension induced by Ca2+. 3. Trifluoperazine (5-100 microM), cyclic AMP (50-300 microM) and cyclic GMP (50-100 microM) each antagonized Ca2+ in a concentration-dependent manner. On the other hand, okadaic acid (OA, 0.2-1 microM) potentiated Ca2+ and increased the maximum response to Ca2+ (+25 +/- 5.4%, n = 5, for 1 microM OA). 4. This study has demonstrated the high Ca2+ sensitivity of the activation mechanism of human isolated bronchial smooth muscle. It also suggests that control of the contractile machinery in the human bronchus involves processes of phosphorylation and dephosphorylation. The Beta-Escin-treated human bronchus may be a useful model for investigating the cellular basis of some pathophysiological processes such as bronchial hyper-responsiveness.

  • Diosmin‐induced increase in sensitivity to Ca2+ of the smooth muscle contractile apparatus in the rat isolated femoral vein
    British journal of pharmacology, 1994
    Co-Authors: Jean-pierre Savineau, Roger Marthan
    Abstract:

    The effect of diosmin, a flavone derivative, on the Ca2+ sensitivity of the venous contractile apparatus was investigated in chemically (Beta-Escin) skinned strips from the rat isolated femoral vein. Diosmin (0.5-10 microM) shifted to the left the concentration-response curve to Ca2+ (0.05-5 microM). The maximal effect was observed in the presence of 1 microM diosmin which increased the contractile response evoked by 0.15 microM Ca2+ from 26.3% to 78.9% of the maximal Ca(2+)-induced response. This work demonstrates that the venotonic action of diosmin involves an increase in the Ca2+ sensitivity of the contractile apparatus. Such a mechanism of action could represent a new and important means of therapeutic control of vasomotor activity.

A Kitabatake - One of the best experts on this subject based on the ideXlab platform.

  • A role of myofilament Ca2+ sensitivity in enhanced vascular reactivity in cardiomyopathic hamsters.
    European journal of pharmacology, 1998
    Co-Authors: A Sato, Y Hattori, M Kanno, M Fukao, I Sakuma, A Kitabatake
    Abstract:

    We compared the contractile responses to vasoconstrictors in aortas from 20- to 22-week old cardiomyopathic hamsters, BIO 53.58 strain, and age-matched F1b strain controls. Aortas from cardiomyopathic hamsters exhibited greater contractions in response to phenylephrine, angiotensin II, and high K+ than did the controls. Neither endothelium removal nor the presence of indomethacin and N(omega)-nitro-L-arginine (L-NNA) affected the enhanced contractile responses to these vasoconstrictors, indicating no involvement of endogenous prostanoids and nitric oxide from the endothelium. The contractile response to phorbol-12,13-dibutyrate (PDB) was also more markedly increased in cardiomyopathic aortas regardless of whether extracellular Ca2+ was present. The contractile response of cardiomyopathic aorta to phenylephrine was more sensitive to the inhibitory actions of the protein kinase C inhibitors staurosporine and calphostin C than was that of control aorta. These results suggest that activation of protein kinase C is partly involved in the enhanced phenylephrine response of cardiomyopathic aorta. None of nifedipine, ryanodine, and cyclopiazonic acid modified the maximum contractions induced by phenylephrine in either cardiomyopathic aortas or controls. The Ca2+ sensitivity of tension was significantly increased in Beta-Escin-skinned smooth muscle of mesenteric artery from cardiomyopathic hamsters compared to that of controls. PDB induced Ca2+ sensitization, but significantly only in cardiomyopathic hamsters. We propose that the enhanced vascular reactivity in cardiomyopathic hamsters may primarily result from increased Ca2+ sensitivity of contractile proteins. In addition, protein kinase C-mediated Ca2+ sensitization may further contribute to the enhanced vascular response to agonists.

  • Different regulation of myofilament Ca2+ sensitivity in Beta-Escin-skinned cardiac and vascular smooth muscles.
    European journal of pharmacology, 1997
    Co-Authors: F Tomita, Y Hattori, M Kanno, T Kohya, M Sasaki, A Kitabatake
    Abstract:

    We compared the effects of guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS, an activator of G-protein), phorbol 12,13-dibutylate (PDB, an activator of protein kinase C) and pimobendan (an inotropic agent with Ca2+-sensitizing action) on the Ca2+ sensitivity of the contractile proteins in Beta-Escin-skinned muscle preparations obtained from rabbit left ventricles and mesenteric arteries. After the skinning procedure, when GTPgammaS (100 microM) or PDB (1 microM) was added to the Ca2+ solutions, pCa50 were significantly increased in preparations obtained from vascular smooth muscle, but not from cardiac muscle, indicating that G-protein- and protein kinase C-mediated direct Ca2+ sensitization may occur only in smooth muscle, but not in cardiac muscle. In contrast, pimobendan (50 microM) increased the Ca2+ responsiveness only in cardiac muscle. Therefore, we conclude that, in addition to the common regulatory factors affecting Ca2+ sensitivity such as intracellular pH and phosphorylation by protein kinase A, there are other means of regulation of Ca2+ sensitivity working differently in cardiac and in vascular smooth muscles.