The Effect Of STVNa On Guinea Pig Ventricular Myocytes K_ATP Channel The Study Of Its Mechanism

K_ATP channel is the ATP-sensitive potassium channel,and widely distributed in cardiomyocytes.K_ATP channel is an important mediator or factor in physiological and pathological metabolic pathway.K_ATP channel is inhibited by intracellular ATP and activated by intracellular nucleoside diphosphates,thereby coupling cell metabolic condition to membrane electrical activity.On the other hand,desensitization of the channel to its opener or the metabolic ligand ATP in pathological conditions,like cardiac hypertrophy,would decrease the adaption of myocardium to metabolic stress and is a disadvantage for drug therapy.Isosteviol,obtained by acid hydrolysis of stevioside,has been demonstrated to play a cardioprotective role against diseases of cardiovascular system,like anti-IR injury,antihypertension,antihyperglycemia,ect.In this study,we investigated the effects of isosteviol sodium?the sodium salt of isosteviol,STVNa?on sarcK_ATP currents induced by pinacidil and flavoprotein fluorescence elicited by diazoxide in isolated guinea pig cardiomyocytes.1.We examined the effect of isosteviol sodium?STVNa?on sarcK_ATP channel current by preincubating the isolated myocytes with the drug.The results showed that the preincubation with STVNa increased the current density and activated rate of SarcK_ATP Channel elicited by pinacidil.The effect of isosteviol on sarcK_ATP channel currents was time-and dose-dependent.2.We examined the effect of STVNa on the rapidly activated delayed rectifier K+?IKr?and L-type Ca2+ channel?Ica?currents and on the action potential of guinea pig ventricular myocytes.The results showed that STVNa alone had no effect on Ikr,L-type calcium currents and action potential.3.Futher,we also studied the effect of STVNa on mitoK_ATP channel by preincubating the isolated myocytes with STVNa.The results showed that preincubating the cells with 10 ?M STVNa significantly enhanced the intensity of diazoxide-induced flavoprotein fluorescence.The normalized fluorescence intensity for STVNa-preincubated group was about 2.5 times larger than the control group,P < 0.05.STVNa alone without the use of diazoxide did not induce an obvious flavoprotein fluorescence compared with baseline.4.To examine the effects of ROS on the enhancing character of STVNa on the sarcK_ATP channels and mitochondrial flavoprotein oxidation were mediated by Reactive oxygen species?ROS?,the ROS scavenger NAC was coadministered.The results showed that coadministering with 100 ?M NAC blocked the enhancing effect of STVNa.NAC?100 ?M?alone had no effects on pinacidil-elicited sarcK_ATP channel current.For mitochondria,NAC also blocked the potentiation effect of STV on diazoxide-elicited flavoprotein fluorescence.Similarly,NAC?100 ?M?alone had no effect on the fluorescence intensity of flavoprotein elicited by diazoxide.Conclusions:?1?STVNa can increase the sensitivity of sarcK_ATP channel and mitoK_ATP channel;?2?STVNa has no effect on the L-type calcium current,Ikr currents and action potentials;?3?The effects of STVNa on sarcK_ATP channel and mitoK_ATP channel were ROS dependent.