The Effect Of Polydatin On Calcium And Potassium Channels In Rat Ventricular Myocytes

Object: Polydatin (3,4′,5-trihydroxystibene-3-β-mono-D-gluco-side),also called piceid, is a monocrystalline isolated from a traditional Chineseherbal medicine, polygonum cuspidatum. Polydatin has been proved to havenumerous biological effects. In recent years, the beneficial effect of polydatinhas been found in different organs. It has been demonstrated that polydatin hasprotective effect on brain, lung, intestinal and heart against ischemia-reperfusion injury. Also it has been reported that polydatin has anti-inflammatory, anti-shock injury, anti-oxidation and anti-platelet aggregationeffects.Our previous study demonstrated that polydatin had obvious cardio-protective effect against ischemia/reperfusion injury and arrhythmia. Theelectrophysiological research showed that polydatin shortened duration ofrepolarization of action potential (AP) in normal papillary muscles anddecreased overshoot (OS), amplitude of action potential (APA) and maximalrate of depolarization in phase0(Vmax) in partially depolarized papillarymuscles, which might be one of electrophysiological mechanism for polydatinantiarrhythmia. It is well known that action potential results fromtransportation of different ion channels in cell membrane. But the ionicmechanism for polydatin antiarrhythmia remains obscure. The aim of thisstudy was to investigate the effect of polydain on L-type calcium channel(I_Ca-L), transient outward potassium current (I_to), steady-state outwardpotassium current (I_ss), inward rectifier potassium current (I_K1), and ATPsensitive potassium current (I_KATP) in ventricular myocytes of rat using thewhole-cell patch clamp technique.Methods: Male adult rat was used in this study and the single ventricularmyocytes were isolated by Langendorff technique with the enzymatic dissociation method. The myocytes were placed on the bottom of recordingchamber mounted on the stage of inverted microscope, perfused with normalexternal solution in constant temperature and speed. Under controlling ofmicromanipulator, the glass microelectrode was attached to the cell membraneto form the giga seal,then give the membrane a brief negative pressure toobtain the whole-cell patch clamp mode. The current was induced and collectby running different pclamp program in voltage clamp mode. The differentconcentration of polydatin was used cumulatively and effect of polydatin onI_Ca-L, I_to, I_ss, I_K1,I_KATPwas investigated.Results:(1) polydatin has an inhibitory effect on L-type Ca²⁺current inventricular myocytes. Polydatin decreased the density of I_Ca-Lin aconcentration-dependent manner. Under the concentration of25μM,50μM,75μM,100μM, the decrease of peak I_Ca-Lwas17.5%,32.1%,40.5%and52.6%, respectively (P<0.01). The I-V relation curve of I_Ca-Lwas graduallyelevated with the increase of Polydatin concentration, but the I-V relation-ship of I_Ca-Lwas not changed. Polydatin had no effect on the activation curveof I_Ca-Land recovery from inactivation, but shift inactivation curve of I_Ca-Ltoward negative potential (-7.4mV).(2) polydatin has an activation effect oninward rectifier potassium current and ATP-sensitive potassium current inventricular myocytes. Under-120mV test potential, polydatin at10,50,100μM increased density of peak I_K1significantly compared with baseline I_K1, theincreasement of peak I_K1was35.0%,18.4%and20.8%, respectively (P<0.05).At60mV and-120mV of test potential, outward and inward I_KATPwereincreased for66.2%and144.6%by50μM polydatin, respectively (P<0.05).(3)polydatin has no effect on transient outward K+current and steady-stateoutward potassium current in ventricular myocytes. The diffenrentconcentration of polydatin has no action on the peak amplitude of I_to, the I-Vrelationship, activation curve, inactivation curve and recovery frominactivation (P>0.05). Also polydatin has no effect on I_ss(P>0.05).Conclusion: Polydatin inhibits L-type Ca²⁺channel in a concentration-dependent manner through accelerating the inactivation of the channel in rat ventricular myocytes, and activates I_K1and I_KATPchannels, which might be theionic mechanisms for polydatin cardiac protective and antiarrhythmic effects.