Effects Of Osthol On Ion Channels In Ventricular Myocytes Of Rats

Objective:The function of ion channel plays a key role in the formation and conduction of action potential of cardiac muscle cells, especially the voltage dependent channel. The main task of this paper is to study the ionic mechanism of the excitability of the atrial and ventricular myocytes by using the patch clamp technique and to investigate the electrophysiological effects of Osthole (Ost) on INa and Ito in rat ventricular myocytes, including Ⅰ-Ⅴ curves、activation kinetics、 inactivation kinetics and recovery kinetics, to investigate the possible effects and mechanism of Ost on heart.Methods:Langendroff perfusion apparatus and collagenase Ⅱ are used to isolate ventricular myocytes from Sprague-Dawley rats. Ost was added into the suspension of the myocytes. Whole cell patch-clamp technique was used to record the INa and Ito in the ventricular myocytes.Results:1. We found that density of fast inward INa was about 30% greater in atrial myoeyte than that in ventrieular myocyte..The V1/2 of ativation and inactivation of INa are smaller in atrial myoeytes (-44.65±0.26 mv,-101.1±0.26mv) than that in ventricular myocytes(-42.45.0±0.61 mv,-81.0±0.45 mv).The tau of the atrial myocytes (26.77±0.03ms) is longer than that in ventricular myocytes (15.99±0.06 ms).2. Ost (>100μM) inhibited INa in a time and concentration-dependent manner. The Ⅰ-Ⅴ curves of the sodium current were upward obviously with inhibiting the peak current density from (-29.8314.21) pA/pF to (-20.11±3.72) pA/pF and (-17.74±5.71) pA/pF (P<0.01,n= 10) at concentration of 100μM and 300μM,but the activation potential and peak potential did not change.The activation curve of INa move to left. Besides,osthole caused significant hyperpolarizing shifts in voltage-dependent channel inactivation of INa and slower recovery from inactivation at certain concentration.100 μM and 300μM Ost shifted the V1/2 of INa from(-81.10±0.35) mV in control to (-91.62±1.06) mV and (-100.60±0.21) mV and τ increased from (15.09±0.78) ms in control to (23.41±1.23) ms and (31.62±0.97) ms (P＜0.01, n=10).3. Osthole (>300μM) inhibited transient outward potassium current in a time and concentration-dependent.300μM osthole inhibit the peak current density from (33.75±3.60) pA/pF to (11.52±2.41) pA/pF at+60 mv (P＜0.01, n=10). The activation curve of Ito also move to left. Besides,osthole caused significant hyperpolarizing shifts in voltage-dependent channel inactivation of Ito and slower recovery from inactivation at certain cencentration.100 and 300 μM osthole shifted the W1/2 of Ito from (-38.48±0.92) mV to (-49.48±1.54) mV and(-74.34±0.79) mV (P＜0.01, n=10). 100μM osthole had little effect on recovery from inactivation.300μM osthole (τ=141.1±1.66 ms) resulted in shifteward of the curves of recovery compared to the control (τ=70.09±1.32 ms) (n=10, P<0.01)Conclusion:The atrial and ventricular myocytes of rat shows a distinct electrophysiological characteristics.Besides,Ost can block INa and Ito with different degrees in ventricular myocytes when it reaches some concentration.