Effect Of Tannic Acid On Calcium Currents, Calcium Transient And Contractility In Rat Ventricular Myocytes

Objective: Tannic acid?TA?is a group of water-soluble polyphenolic compounds that occur mainly in plant food,particularly in bananas,grapes,sorghum,spinach,persimmons,coffee,chocolate,and tea.TA is also present in significant amounts in red wine.As red wine consumption has been associated with a low heart disease rate in France despite a high cholesterol diet in this population,we hypothesized that TA may contribute to this phenomenon dubbed the ‘French Paradox'?L-type Ca²⁺ channels?LTCCs?are mediators and regulators of Ca²⁺ influx and are pivotal in the function and dysfunction of cardiac myocytes.L-type calcium current(I_Ca-L)is important in heart function because it triggers excitation–contraction coupling,modulates action potential shape and is involved in cardiac arrhythmia.The inhibitory effects of calcium channel blockers on LTCCs can result in decrease of Ca²⁺ influx and the intracellular calcium,reduction of cardiac contractility and reduction of the myocardial oxygen consumption.In recent studies,we explored that TA could exert cardioprotective effects against ISO-induced myocardial ischemia injury.Increased myocardial contractility is the main characteristic of ischemic cardiomyopathy heart reactions.Rising of [Ca²⁺] could cause enhanced contractility and trigger some associated pathological changes such as hypertrophy and apoptosis.Some drugs can effectively protect the myocardium from ischemic injury by suppressing cardiac the L-type calcium currents and contractility like Ca²⁺ antagonists and ?-adrenoceptor blocking agents.Based on a survey of the literature,no scientific report has systematically demonstrated cellular and ion channel mechanisms of TA in cardiovascular protective effects,although TA is one of the main ingredients in red wine.The aim of this work was to observe the effects of TA on L-type Ca²⁺ channels,Ca²⁺ transient and contractility in rat ventricular myocytes under physiological conditions and to investigate the mechanism of cardiovascular protection mediated by these effects in rat ventricular myocytes using the whole-cell patch-clamp recording technique,video-based edge detection and dual excitation fluorescence photomultiplier systems.Methods:In present experiment,the whole-cell patch-clamp techniques and video-based edge detection and dual excitation fluorescence photomultiplier systems were used to research the effects of TA on L-type Ca²⁺ current(I_Ca-L),Ca²⁺ transient and contractility of isolated rat ventricular myocytes?Results:1 Confirmation of L-type calcium channel current(I_Ca-L)I_Ca-L was elicited under the steady-state activation protocol.Verapamil at 100 m?44?almost completely blocked the current?P < 0.01?,demonstrating that it was I_Ca-L?2 Concentration-dependent Effects of TA on I_Ca-LDifferent concentrations of TA were found to inhibit I_Ca-L,the concentration-dependent relationship was described by a logistic equation,where the concentration of TA producing a half-maximal inhibitory concentration?IC50?was 1.69 ± 0.19 ?M.The inhibition rates of 0.3,1,3,10 and 30 ?M TA on I_Ca-L were 8.16 ± 0.66%,18.80 ± 0.78%,29.60 ± 1.62%,40.36 ± 1.52% and 46.15 ± 2.10%,respectively?3 Effects of TA on Current-voltage Relationship of I_Ca-LThese results demonstrated that 3 and 10 ?M TA could reduce the maximum current by a significant margin?4 Effects of TA on Steady-state Activation and Inactivation of I_Ca-LThe V1/2 value for steady-state activation of I_Ca-L in the control was-15.80 ± 0.84 mV with a slope factor?k?of 8.26 ± 0.79 mV.Meanwhile,values of V1/2 for activation with 3 and 10 ?M TA were-19.66 ± 0.28 mV with a k value of 6.52 ± 0.26 mV and-21.20 ± 0.28 mV with a k value of 6.19 ± 0.26 mV,respectively.In the absence of TA,the V1/2 of the inactivation was-34.94 ± 0.43 mV with a k value of 4.92 ± 0.36 mV.In the presence of 3 and 10 ?M TA,values of V1/2 for inactivation were-37.06 ± 0.07 mV with a k value of 5.00 ± 0.06 mV and-38.64 ± 0.07 mV with a k value of 5.44 ± 0.06 mV,respectively?5 Effects of TA on I_Ca-L of Ventricular Myocytes from Rat Hearts with Myocardial IschemiaAt the concentrations of 3 and 30 ?M,TA could significantly inhibit I_Ca-L by 11.92 ± 0.82% and 23.44 ± 1.19%?Fig.6??6 Effects of TA on Myocyte Shortening and Calcium TransientsUpon exposure to TA,the peak of the amplitude gradually declined.The results showed that TA at the concentration of 0.3 ?M could significantly inhibit myocyte shortening by 19.19 ± 3.46%?n = 5¹3,P < 0.05?and decreased the amplitude of the Ca²⁺ transient by 13.87 ± 6.29%?n = 5,P < 0.05??7 Effects of TA on Time to 10% of The Peak?Tp?and Time to 10% of The Baseline?Tr?The Tp is a characterization of the speed of contraction or Ca²⁺ elevation,representing the time from t0 to 10% of the peak value.Meanwhile,Tr is a characterization of cellular relaxation or Ca²⁺ reuptake.Compared with the control group,TA at 0.3 ?M significantly increased the Tp?P < 0.01,respectively?,while Tr tended to be slightly prolonged after TA treatment?Conclusions: The results showed that TA significantly inhibited L-type Ca²⁺ channel.In addition,TA reduced Ca²⁺ transient and contractility in adult rat ventricular myocytes.These findings may be associated with the cardiovascular protective effects of TA?...