Effects Of Hydrogen Sulfide On Electrophysiology Of Cardiomyocytes

Hydrogen sulfide (H2S) has been proved to be the third endogenous signaling gasotransmitter, besides nitric oxide (NO) and carbon monoxide (CO), and shows the important physiological functions. It is now clear that H2S has the vasorelaxant function. In vascular smooth muscle cells (VSMCs), the opening of ATP-sensitive potassium channels (KATP channels) and the entrance of extracellular calcium were reported to be involved in H2S actions. KATP channels widely distribute in heart cells. It is known that the opening of KATP channels in myocardium is an important endogenous cardioprotective mechanism. Recently, H2S has been found to play a negative inotropic role in the heart and could be endogenously produced by the cardiac tissues as a physiological cardiac function regulator. And this effect of H2S is mediated by KATP channel pathway. Endogenous H2S can be generated from L-cysteine catalyzed by two pyridoxal-5'-phosphate-dependent enzymes, cystathionineβ-synthase (CBS) and cystathionineγ-lyase (CSE). H2S is directly produced in myocardial tissues, arterial and venous tissues by CSE. The purpose of this study is to investigate the effects of H2S on electrophysiology of cardiomycytes and underlying mechanisms by using intracellular microelectrode technique.1 Electrophysiological effects of hydrogen sulfide on guinea pig papillary musclesAim: To study the electrophysiological effects of hydrogen sulfide (H2S) on guinea pig papillary muscles.Methods: Parameters of action potentials (APs) were recorded using intracellular microelectrodes and were analyzed with the system of sampling and processing cardiac transmembrane potential designed by our department.Results: (1) H2S (50μmol/L) decreased the plateau period duration (PPD) from 120.6±3.1 ms to 109.9±3.3 ms (P <0.01), 50% of duration of action potential (APD50) from 157.2±3.8 ms to 144.7±3.9 ms (P <0.01), 90% of duration of action potential (APD90) from 179.3±3.6 ms to 167.6±2.9 ms (P <0.01), duration of action potential (APD) from 190.1±4.1 ms to 179.2±4.6 ms (P <0.05); H2S (100μmol/L) decreased PPD from 120.6±3.1 ms to 97.2±3.8 ms (P <0.01), APD50 from 157.2±3.8 ms to 129.0±4.5 ms (P <0.01), APD90 from 179.3±3.6 ms to 153.8±4.1 ms (P <0.01), APD from 190.1±4.1 ms to 166.2±3.7 ms (P <0.01); H2S (200μmol/L) decreased PPD from 120.6±3.1 ms to 71.7±3.6 ms (P <0.001), APD50 from 157.2±3.8 ms to 98.3±4.2 ms (P <0.001), APD90 from 179.3±3.6 ms to 122.8±3.8 ms (P <0.001), APD from 190.1±4.1 ms to 135.2±3.5 ms (P <0.001), and decreased the amplitude of action potential (APA) from 119.0±3.1 mV to 116.3±2.3 mV (P<0.05). (2) In partially depolarized papillary muscles, H2S (100μmol/L) decreased PPD from 98.2±4.2 ms to 78.4±4.3 ms (P <0.01), APD50 from 130.1±5.6 ms to 106.3±5.7 ms (P <0.01), APD90 from 142.3±5.4 ms to 119.0±6.2 ms (P <0.05), APD from 154.5±5.3 ms to 127.9±4.9 ms (P <0.01), APA from 91.3±2.8 mV to 80.4±2.1 mV (P <0.01), overshoot (OS) from 35.8±3.1 mV to 25.9±3.8 mV (P <0.001), and maximal rate of depolarization in phase 0 (Vmax) from 31.8±5.1 V/s to 17.5±4.5 V/s (P <0.01). (3) Pretreatment with KATP channel blocker glibenclamide (Gli; 20μmol/L) could partially block the effects of H2S (100μmol/L). (4) Pretreatment with L-type Ca2+ channel agonist Bay K8644 (0.5μmol/L) could partially block the effects of H2S (100μmol/L). (5) Pretreatment with Ca2+-free K-H solution containing Gli (20μmol/L) could completely block the effects of H2S (100μmol/L). (6) APD in normal papillary muscles was increased by DL-propargylglycine (PPG, an inhibitor of CSE; 200μmol/L).Conclusion: All these results suggest that the effects of H2S on papillary muscles are due to an increase in potassium efflux through opening the KATP channels and a decrease in calcium influx. Endogenous H2S may act as an important regulator in electrophysiological characters in papillary muscles. 2 Electrophysiological effects of hydrogen sulfide on pacemaker cells in sinoatrial nodes of rabbitsAim: To study the electrophysiological effects of hydrogen sulfide (H2S) on isolated pacemaker cells in sinoatrial (SA) nodes of rabbits and its possible action mechanism.Methods: Parameters of action potentials (APs) were recorded using intracellular microelectrodes and were analyzed with the system of sampling and processing cardiac transmembrane potential designed by our department.Results: (1) H2S (50μmol/L) decreased the velocity of diastolic (phase 4) depolarization (VDD) from 63±12 mV/s to 49±13 mV/s (P <0.05), rate of pacemaker firing (RPF) from 179±14 beat/min to 163±13 beat/min (P <0.05); H2S (100μmol/L) decreased VDD from 63±12 mV/s to 38±10 mV/s (P <0.01), RPF from 179±14 beat/min to 151±10 beat/min (P <0.01); H2S (200μmol/L) decreased VDD from 63±12 mV/s to 22±11 mV/s (P <0.01), RPF from 179±14 beat/min to 134±16 beat/min (P <0.01). (2) Pretreatment with KATP channel blocker glibenclamide (Gli; 20μmol/L) could block the effects of H2S (100μmol/L). (3) Pretreatment with CsCl (2 mmol), a blocker of If, did not affect the effects of H2S on SA node cells. (4) An inhibitor of cystathionineγ-lyase (CSE), DL-propargylglycine (PPG, 200μmol/L), did not affect parameters of action potentials of pacemaker cells in SA nodes.Conclusion: All these results suggest that H2S exertes a negative chronotropic action on pacemaker cells in SA nodes of rabbits. These effects are likely due to an increase in potassium efflux through opening KATP channels; If is unlikely to play a major role in these effects. And in our study, it does not be found that in SA nodes endogenous H2S is generated by CSE to exhibit electrophysiological effects on pacemaker cells.