Effects Of Hydrogen Sulfide On Electrophysiology Of Ischemic 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. Endogenous H2S can be generated from L-cysteine catalyzed by two pyridoxal-5′-phosphate-dependent enzymes, cystathionie-β-synthase (CBS) and cystathionine-γ-lyase (CSE). H2S is directly produced in myocardial tissues, arterial and venous tissues by CSE. It is now clear that H2S has the vasorelaxtant functions. 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, which is mediated by KATP channel pathway. In the normal papillary muscles exogenous H2S can decrease the duration of action potential (APD) in a concentration-dependent manner, And in partially depolarized papillary muscles H2S can also decrease the amplitude of action potential (APA), overshoot (OS) and maximal velocity of depolarization at 0 (Vmax) beside the APD. Though the cardioprotection of H2S on ischemia heart had been reported, the electrophysiological effects of H2S on ischemic cardiomyocytes were not clear. The purpose of this study is to investigate the effects of H2S on electrophysiology of ischemic cardiomycytes and its underlying mechanisms by using intracellular microelectrode technique.Aim: To study the electrophysiological effects of hydrogen sulfide (H2S) on ischemic guinea pig papillary muscles. Methods: 1. Parameters of action potentials (APs) of the ischemic guinea pig papillary muscles were recorded using intracellular microelectrodes and analyzed with the system of sampling and processing cardiac transmembrane potential designed by our department. 2. The ultrastructure of papillary muscle cells observed by transmission electron microscope to prove the electrophysiological's changes of structure background due to different treatments.Results: 1.(1). H2S pretreatment (50μmol/L,100μmol/L,200μmol/L) changed the plateau period duration (PPD), duration of action potential (APD), 50% of APD (APD50), 90% APD(APD90), and maximal rate of depolarization at phase 0 (Vmax) of ischemic guinea pig papillary muscles in a concentration-dependent manner. H2S pretreatment promoted shortening of APD, APD50, APD90, PPD and Vmax at the early phase of ischemia, and improving of APD, APD50, APD90, PPD and Vmax at the late phase of ischemia, there is a significant changment compaired with ischemia. (2). The parameters of PPD,APD50,APD90,APD and Vmax had similar changes reduced by exogenous H2S pretreatment after ischemic preconditioning. (3). Pretreatment with KATP channel blocker glibenclamide (Gli; 20μmol/L) could partially block the effects of H2S pretreatment (100μmol/L). (4). The shortening of parameters PPD,APD50,APD90,APD and Vmax were weakened at the early phase of ischemia and the improving of these parameters were decreased at the late phase of ischemia by DL-propargylglycine (PPG, an inreversible inhibitor of CSE; 200μmol/L). 2. (1). The ultrastructure of normal guinea pig papillary muscle cell showing the sarcomere and light dark band were clear, mitochondria and glycogenosome were abundant, and mitochondrial cristae and membrane were clear. (2). The TEM showing the sarcomere was in a bad apposition, Sarcoplasmic reticulum dilated, cytoplasmic was edema, glycogenosome decreased, mitochondrial cristae and membrane were anastomosis or absence. (3). The damage of ultrastructure given ischemia insult relieved by ischemic preconditioning or H2S pretreatment. (4). Glibenclamide could block the protect effect of papillary muscle ultrastructure due to H2S pretreatment. (5). The ultrastructure's observation of the ischemic papillary muscle cell after PPG preteatment. Papillary muscle was severe edema; sarcomeres were in bad arrangement, containing breakage or abolition. The quantity of mitochondria and glycogenosome decreased significantly. Mitochondria cristae and membrane in a great measure were anastomosis or vacuolization.Conclusion: All these results suggest that effects of H2S on papillary muscles are due to an increase in potassium efflux through opening the KATP channels at the early phase of ischemia, and acceleration in potassium reuptake through improving the Na+-K+-ATPase at the late phase of ischemia. Endogenous H2S may act as important regulator in electrophysiological characters in ischemic papillary muscles. The observation of papillary muscle cell's ultrastructure showed that exogenous H2S could decrease the damage of ischemic guinea pig papillary muscles. The absence of endogenous H2S could aggravate the damage of papillary muscle cell's ultrastructure when the papillary muscle insulted ischemia.