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James N Weiss - One of the best experts on this subject based on the ideXlab platform.

  • connexin 43 hemichannels opened by Metabolic Inhibition
    Journal of Biological Chemistry, 1999
    Co-Authors: Scott A John, Richard P Kondo, Shengyong Wang, Joshua I Goldhaber, James N Weiss
    Abstract:

    Abstract The cause of altered ionic homeostasis leading to cell death during ischemia and Metabolic Inhibition is unclear. Hemichannels, which are precursors to gap junctions, are nonselective ion channels that are permeable to molecules of less thanM r 1000. We show that hemichannels open upon exposure to calcium-free solutions when they are either heterologously overexpressed in HEK293 cells or endogenously expressed in cardiac ventricular myocytes. In the presence of normal extracellular calcium, hemichannels open during Metabolic Inhibition. During ischemia and other forms of Metabolic Inhibition, activation of relatively few hemichannels will seriously compromise the cell’s ability to maintain ionic homeostasis, which is an essential step promoting cell death.

  • ATP‐sensitive K+ channel modification by Metabolic Inhibition in isolated guinea‐pig ventricular myocytes.
    The Journal of Physiology, 1993
    Co-Authors: N Deutsch, James N Weiss
    Abstract:

    1. ATP-sensitive K+ (K+ATP) channels are believed to make an important contribution to the increased cellular K+ efflux and shortening of the action potential duration (APD) during Metabolic Inhibition, hypoxia, and ischaemia in the heart. The mechanisms by which the activity of the K+ATP channel is regulated during conditions of Metabolic impairment are not completely clear. Extrinsic factors such as increased [ADP]i, acidosis, and stimulation of adenosine receptors appear to decrease the K+ATP channel's sensitivity to closure by [ATP]i. The purpose of this study was to determine whether the K+ATP channel itself is intrinsically altered by the processes associated with Metabolic impairment. 2. Isolated guinea-pig ventricular myocytes were Metabolically inhibited in glucose-free 1.8 mM Ca2+ Tyrode solution containing 9 microM rotenone and 0.9 microM carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) while recording unitary currents through K+ATP channels in cell-attached patches. When K+ATP channel activity became maximal, the patch was excised (inside-out) into 150 mM K+ bath solution containing different ATP concentrations. The Kd for suppression by [ATP]i ([ATP]i causing half-maximal suppression of current through K+ATP channels) was markedly increased to 305 microM (n = 9) compared to patches excised from control myocytes not exposed to Metabolic inhibitors (Kd = 46 microM, n = 28). 3. A [Ca2+]i-dependent process was involved in K+ATP channel modification during Metabolic Inhibition. Removal of extracellular Ca2+ during Metabolic Inhibition led to an intermediate decrease in the ATP sensitivity of the K+ATP channels (Kd = 120 microM, n = 6). In myocytes that were pretreated with 10 microM ryanodine in addition to removing extracellular Ca2+, the reduction in ATP sensitivity was completely prevented (Kd = 23 microM, n = 6). 4. In inside-out membrane patches excised from control non-Metabolically inhibited myocytes, elevated free [Ca2+]i (2 microM) did not alter the sensitivity of the K+ATP channel to closure by [ATP]i, suggesting that in Metabolically inhibited myocytes elevated [Ca2+]i acted indirectly. K+ATP channel run-down was found to increase the sensitivity of K+ATP channels to closure to [ATP]i (Kd = 16 microM, n = 13). 5. Inside-out membrane patches excised from control non-Metabolically inhibited myocytes were also exposed to various proteases, phospholipases and other reagents that may be activated during Metabolic Inhibition. Trypsin and chymotrypsin treatment increased the Kd from 39 to 213 microM (n = 8) and 110 microM (n = 5), respectively. Calpain I had no apparent effect on the Kd.(ABSTRACT TRUNCATED AT 400 WORDS)

  • Mechanisms of excitation-contraction coupling failure during Metabolic Inhibition in guinea-pig ventricular myocytes.
    The Journal of Physiology, 1991
    Co-Authors: Joshua I Goldhaber, J M Parker, James N Weiss
    Abstract:

    1. The effects of complete Metabolic Inhibition on excitation-contraction coupling in heart were studied by exposing patch-clamped guinea-pig ventricular myocytes, loaded via the patch pipette with the Ca2+ indicator Fura-2 (0.1 mM), to carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP, 1 microM) and 2-deoxyglucose (2-DG, 10 mM) while simultaneously recording membrane current, Fura-2 fluorescence, and cell motion. The patch pipette solution contained Cs+ and TEA (tetraethylammonium) to partially block K+ currents. 2. During voltage clamps from a holding potential of -40 mV to a test potential of 0 mV, complete Metabolic Inhibition decreased the Ca2+ current (ICa), activated the ATP-sensitive K+ current, modestly elevated diastolic [Ca2+]i and markedly reduced the [Ca2+]i transient without altering its voltage dependence. Active shortening was impaired and diastolic cell length decreased prior to large increases in diastolic [Ca2+]i, consistent with rigor induced by ATP depletion. Return of the [Ca2+]i transient to baseline and relaxation upon repolarization were also delayed. 3. Despite the depression of the peak [Ca2+]i transient induced by membrane depolarization during Metabolic Inhibition, the [Ca2+]i transient induced by a rapid exposure to 5 mM-caffeine was greater than control. The Na(+)-Ca2+ exchange current during the caffeine-induced [Ca2+]i transient was not affected by Metabolic Inhibition. 4. [Ca2+]i transients depressed by Metabolic Inhibition could be enhanced by augmenting ICa with elevated [Ca2+]o (10 mM) and Bay K 8644 (5 microM). 5. To study the relationship between the magnitude of ICa and the amplitude of the [Ca2+]i transient, ICa was modulated either by (a) voltage clamping the cell to different membrane potentials at constant [Ca2+]o or by (b) rapidly altering [Ca2+]o immediately prior to a voltage clamp to a fixed membrane potential. Under control conditions, the relationship between the size of ICa and the magnitude of the [Ca2+]i transient was the same whether ICa was modulated by altering membrane potential or [Ca2+]o, suggesting that membrane potential does not significantly modulate the Ca(2+)-induced Ca2+ release mechanism of cardiac excitation-contraction coupling. 6. After Metabolic Inhibition, however, the same ICa released less Ca2+ than under control conditions, consistent with some impairment of the Ca2+ release mechanism. 7. These results suggest that under conditions in which excitability is maintained by controlling membrane voltage and minimizing Metabolically sensitive K+ currents, the decreased [Ca2+]i transient observed during Metabolic Inhibition severe enough to induce rigor is caused primarily by depression of ICa and not by depletion of intracellular Ca2+ stores. Additional factors also modestly hinder Ca2+ release from intracellular stores during Metabolic Inhibition.

Tak-ming Wong - One of the best experts on this subject based on the ideXlab platform.

  • Role of reverse mode Na+/Ca2+ exchanger in the cardioprotection of Metabolic Inhibition preconditioning in rat ventricular myocytes.
    European Journal of Pharmacology, 2007
    Co-Authors: Shu-zhuang Li, Feng Wu, Bo Wang, Yi-min Zang, Jing-jun Zhou, Tak-ming Wong
    Abstract:

    Abstract This study determined the role of the reverse mode Na+/Ca2+ exchanger (NCX) in cardioprotection of Metabolic Inhibition preconditioning in isolated ventricular myocyctes. Activity of the reverse mode NCX was assessed by changes of [Ca2+]i upon withdrawal of extracellular Na+. [Ca2+]i was measured by spectrofluorometry, using Fura-2 as Ca2+ indicator. The amplitude of contraction and exclusion of trypan blue by myocytes served as indices of contractile function and viability, respectively. Firstly, NCX activity significantly decreased during simulated reperfusion after severe Metabolic Inhibition (index ischaemia) in myocytes subjected to Metabolic Inhibition preconditioning. This inhibitory effect on NCX activity correlated with the enhancing effect of Metabolic Inhibition preconditioning on cell viability following ischaemic insult. Treatment myocytes with E4031, an activator of reverse mode NCX, during index ischaemia and reperfusion attenuated the enhancing effects of Metabolic Inhibition preconditioning on cell contraction and viability. Secondly, NCX activity was significantly higher at the end of Metabolic Inhibition preconditioning. More importantly, E4031 pretreatment mimicked the beneficial effects of Metabolic Inhibition preconditioning in myocytes and ischaemic preconditioning in the isolated perfused heart, respectively, and these effects were abolished by KB-R7943, an inhibitor of reverse mode NCX. The results indicate that increased reverse mode NCX activity during preconditioning triggered cardioprotection, and reduced reverse mode NCX activity during reperfusion after index ischaemia conferred cardioprotection.

  • cardioprotection of preconditioning by Metabolic Inhibition in the rat ventricular myocyte involvement of κ opioid receptor
    Circulation Research, 1999
    Co-Authors: Shuilin Wu, Hongyu Li, Tak-ming Wong
    Abstract:

    Abstract —To determine whether opioid receptors (ORs) are involved in the delayed cardioprotection of ischemic preconditioning (IP), the effect of severe Metabolic Inhibition (MI) with a glucose-free buffer that contained sodium cyanide and 2-deoxy-d-glucose on the viability of isolated rat ventricular myocytes was first determined 20 hours after preconditioning with a sublethal Metabolic Inhibition (MIP) with a glucose-free buffer that contained 2-deoxy-d-glucose and lactate for 30 minutes in the presence of OR antagonists. With the use of trypan blue exclusion as an index of cell viability, severe MI killed >60% of the cells and the value increased significantly after MIP. In the presence of 5×10 −6 mol/L nor-binaltorphimine (nor-BNI), a selective κ-OR antagonist, but not 5×10 −6 mol/L CTOP, a selective μ-OR antagonist, or 5×10 −6 mol/L naltrindole, a selective δ-OR antagonist, the cardioprotection of MIP was significantly attenuated. To verify the role of κ-OR, we studied the effects of severe MI after pretreatment with the κ-OR agonist U50,488H (UP) for 30 minutes. U50,488H at 3×10 −6 to 1×10 −4 mol/L increased cell viability concentration-dependently with an EC 50 of 3.311×10 −6 mol/L. In the presence of 5×10 −6 nor-BNI, the cardioprotection of UP (3×10 −5 mol/L) was blocked. A time course study showed that UP-induced cardioprotection occurred in 2 windows: the first occurred ≈1 hour later and the other occurred 16 to 20 hours later. Additional studies on cell contraction and intracellular Ca 2+ ([Ca 2+ ] i ) revealed that both UP and MIP attenuated the inhibitory effects of severe MI on contractility and electrically induced [Ca 2+ ] i transient in single ventricular myocytes. On blockade of protein kinase C, the delayed cardioprotections of UP and MIP were significantly attenuated. In conclusion, the results of the present study have provided evidence that κ-OR mediates the cardioprotection of MIP, which may involve protein kinase C and [Ca 2+ ] i .

Norio Akaike - One of the best experts on this subject based on the ideXlab platform.

  • Pre- and postsynaptic ATP-sensitive potassium channels during Metabolic Inhibition of rat hippocampal CA1 neurons
    The Journal of Physiology, 2020
    Co-Authors: Nozomu Matsumoto, Sohtaro Komiyama, Norio Akaike
    Abstract:

    Presynaptic and postsynaptic membrane activities during experimental Metabolic Inhibition were analysed in mechanically dissociated rat hippocampal neurons using nystatin-perforated and conventional whole-cell patch clamp recordings. NaCN, an inhibitor of mitochondrial ATP synthesis, induced an outward current across the postsynaptic soma membrane. This current was blocked by tolbutamide, a sulfonylurea, which blocks ATP-sensitive K+ (KATP) channels. The presynaptic effect of Metabolic inhibitors such as NaCN, NaN3, or glucose-free solution was to increase the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs). Tolbutamide had no effect on this increase in mIPSC frequency induced by Metabolic Inhibition. Diazoxide, a KATP channel opener, evoked a similar somatic outward current in a dose-dependent manner. In addition, diazoxide decreased the frequency of mIPSCs in a dose-dependent fashion. Both these pre- and postsynaptic effects of diazoxide were reversed by tolbutamide, suggesting the existence of KATP channels on both pre- and postsynaptic membranes. These results confirm the presence of KATP channels on both the pre- and postsynaptic membranes but indicate that the channels have significantly different sensitivities to Metabolic Inhibition.

  • Ca2+-activated K+ currents in rat locus coeruleus neurons induced by experimental ischemia, anoxia, and hypoglycemia.
    Journal of neurophysiology, 1997
    Co-Authors: Yoshio Murai, Hisayoshi Ishibashi, S. Koyama, Norio Akaike
    Abstract:

    Ca2+-activated K+ currents in rat locus coeruleus neurons induced by experimental ischemia, anoxia, and hypoglycemia. J. Neurophysiol. 78: 2674-2681, 1997. The effects of Metabolic Inhibition on membrane currents and N-methyl--aspartic acid (NMDA)-induced currents were investigated in dissociated rat locus coeruleus (LC) neurons by using the nystatin perforated patch recording mode under voltage-clamp conditions. Changes in the intracellular Ca2+ concentration ([Ca2+]i) during the Metabolic Inhibition were also investigated by using the microfluometry with a fluorescent probe, Indo-1. Removal of both the oxygen and glucose (experimental ischemia), deprivation of glucose (hypoglycemia), and a blockade of electron transport by sodium cyanide (NaCN) or a reduction of the mitochondrial membrane potential with carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone(FCCP) as experimental anoxia all induced a slowly developing outward current (IOUT) at a holding potential of -40 mV. The application of 10(-4) M NMDA induced a rapid transient peak and a successive steady state inward current and a transient outward current immediately after washout. All treatments related to Metabolic Inhibition increased the NMDA-induced outward current(INMDA-OUT) and prolonged the one-half recovery time of INMDA-OUT. The reversal potentials of both IOUT and INMDA-OUT were close to the K+ equilibrium potential (EK) of -82 mV. Either charybdotoxin or tolbutamide inhibited the IOUT and INMDA-OUT, suggesting the contribution of Ca2+-activated and ATP-sensitive K+ channels, even though the inhibitory effect of tolbutamide gradually diminished with time. Under the Metabolic Inhibition, the basal level of [Ca2+]i was increased and the one-half recovery time of the NMDA-induced increase in [Ca2+]i was prolonged. The IOUT induced by NaCN was inhibited by a continuous treatment of thapsigargin but not by ryanodine, indicating the involvement of inositol 1,4, 5-trisphosphate (IP3)-induced Ca2+ release (IICR) store. These findings suggest that energy deficiency causes Ca2+ release from the IICR store and activates continuous Ca2+-activated K+ channels and transient ATP-sensitive K+ channels in acutely dissociated rat LC neurons.

Csaba Szabo - One of the best experts on this subject based on the ideXlab platform.

  • hydrogen sulfide decreases adenosine triphosphate levels in aortic rings and leads to vasorelaxation via Metabolic Inhibition
    Life Sciences, 2008
    Co-Authors: Levente Kiss, Edwin A Deitch, Csaba Szabo
    Abstract:

    Abstract Aims Hydrogen sulfide (H 2 S) at low concentrations serves as a physiological endogenous vasodilator molecule, while at higher concentrations it can trigger cytotoxic effects. The aim of our study was to elucidate the potential mechanisms responsible for the effects of H 2 S on vascular tone. Main methods We measured the vascular tone in vitro in precontracted rat thoracic aortic rings and we have tested the effect of different oxygen levels and a variety of inhibitors affecting known vasodilatory pathways. We have also compared the vascular effect of high concentrations of H 2 S to those of pharmacological inhibitors of oxidative phosphorylation. Furthermore, we measured adenosine triphosphate (ATP)-levels in the same vascular tissues. Key findings We have found that in rat aortic rings: (1) H 2 S decreases ATP levels; (2) relaxations to H 2 S depend on the ambient oxygen concentration; (3) prostaglandins do not take part in the H 2 S induced relaxations; (4) the 3':5'-cyclic guanosine monophosphate (cGMP)–nitric oxide (NO) pathway does not have a role in the relaxations (5) the role of K ATP channels is limited, while Cl − /HCO 3 − channels have a role in the relaxations. (6): We have observed that high concentrations of H 2 S relax the aortic rings in a fashion similar to sodium cyanide, and both agents reduce cellular ATP levels to a comparable degree. Significance H 2 S, a new gasotransmitter of emerging importance, leads to relaxation via Cl − /HCO 3 − channels and Metabolic Inhibition and the interactions of these two factors depend on the oxygen levels of the tissue.

Jinsong Bian - One of the best experts on this subject based on the ideXlab platform.

  • endogenous hydrogen sulfide contributes to the cardioprotection by Metabolic Inhibition preconditioning in the rat ventricular myocytes
    Journal of Molecular and Cellular Cardiology, 2006
    Co-Authors: Zhanning Feng, Philip K Moore, Jinsong Bian
    Abstract:

    Abstract The possible role of hydrogen sulfide (H 2 S) in cardioprotection was investigated in isolated rat ventricular myocytes exposed to severe Metabolic Inhibition (MI) in glucose-free buffer containing 2-deoxy-D-glucose (2-DOG), an inhibitor of glycolysis. Pretreatment (30 min) with NaHS (a H 2 S donor) at concentrations of 10 −5 to 10 −4 mol/L caused a concentration related increase in cell viability and the ratio of rod-shaped cells. A time course study showed that NaHS-induced cardioprotection occurred in 2 time windows (~1 h and 16-28 h). To observe whether endogenous H 2 S may be involved in the delayed cardioprotection response of IP, DL-propargylglycine (PAG) and β-cyano-L-alanine (BCA; two inhibitors of H 2 S biosynthesis) were used. Both drugs significantly attenuated the cardioprotection produced by MI using cell viability, cellular injury index, and electrically-induced [Ca 2+ ] i transients as end-points. These data suggest that endogenous H 2 S plays an important role in the cardioprotection following MI preconditioning. In an attempt to determine the mechanism of the cardioprotective effect of H 2 S, we examined the effect of blocking K ATP channels with glibenclamide (a non-selective K ATP channel blocker), 5-hydroxydecanoic acid (5-HD, a mitochondrial K ATP blocker), and HMR-1098 (a sarcolemmal K ATP blocker). The cardioprotective effects of NaHS were significantly attenuated by glibenclamide and HMR-1098 treatment but not by 5-HD. Inhibition of NO production with L-NG nitroarginine methyl ester (L-NAME) also attenuated the cardioprotection of NaHS. In conclusion, our findings provide the first evidence that H 2 S may protect the heart most probably by activating sarcolemmal K ATP channels and/or provoking NO release and the cardioprotective effects of Metabolic ischemic preconditioning is, at least partially, mediated by endogenous H 2 S.