Effects Of Ibutilide On The Sodium Channel Currents In Right Ventricular Myocytes Of Rabbit Heart

Objective: Ventricular arrhythmias is a common complication, and right ventricular arrhythmias which is the major reason of sudden cardiac death of youth. It is one of the most important task to seek safe and effective new drug to inhibit the arrhythmias.But research of the Right ventricular myocytes sodium channel is not reported.Drug is a major way for arrhythmias, though nondrug way has rapid progresses. Recent study indicated that Ibutilide is a new antiarrhythmic drug in patients with atrial flutter and atrial fibrillation .It is discovered that Ibutilide can prolong the refractory period of ventricle and is also useful to inhibit ventricular arrhythmias in animal experiments. To explore the ion channel mechanism of the Ibutilide's effect on ventricular arrhythmias, we isolated the single rabbit right ventricular cells with enzyme and the INa was recorded by using patch clamp techniques in the whole-cell configuration.Material and methods:1 Experimental animals: Sixty healthy rabbits (Newsland pure white, from Hebei medical university) of either sex weighing 1.5 to 2 kg were used in the study. The rabbits were divided into three groups: (1) Twenty-five rabbits was used in high- concentration of Ibutilide (10^-5 mmol/L).(2) As well as the group of high-concentration, the same rabbits was used in low- concentration of Ibutilide(10^-6mmol/L).(3) In addition, ten rabbits that have not undergone Ibutilide was defined as control group(Con).2 Cell isolation: Single ventricular myocytes of right ventricular free wall were enzymatically dissociated and isolated.3 Current recording and data analysis: the INa was recorded by means of patch clamp whole-cell recording teachniques under voltage clamp. The INa in cells from the Ibtilide groups were compared with cells in the control group.The current recording program is controlled by the pulse+pulsesefit software.The signal is amplified by the EPC-9 patch clamp amplifier.The data were dealt with SPSS 13.0 software package for statistical analysis.Results1 Ibutilide effect on INa I-V curve of right ventricular myocytesThe INa density-voltage relationship (I-V) curves and activation curves were voltage-dependent and showed as"V"type current properties. They were activated at–70mV,reached the maximum at–20mV and reversed at +50mV. Peak INa current density (at -20mV) was significantly reduced in low- concentration of Ibutilide(10 - 6 mmol/L) (–29.74±3.79 pA/pF,n=10 cells) and high-degree of Ibutilide(10^-5 mmol/L) (–18.32±2.82pA/pF,n=10 cells) compared with that in Con (–45.77±4.62pA/pF, n=10cells) , P<0.01. This was not accompanied by a shift in the current density-voltage relationship configuration and did not change their active, peak and reverse potentials.2 Ibutilide effect on the INa steady-state inactivation curve of right ventricular myocytesThe steady-state inactivation curves of INa were voltage-dependent and showed as"reversed S"type. The INa steady-state inactivation curves showed that the membrane potentials for half-maximal inactivation (V0.5) were shifted markedly in the upward direction (that is, to more negative potentials) in high- concentration of Ibutilide(10-5mmol/L) (–103.58±4.6mV,n=10 cells)and low-concentration of Ibutilide(10^-6mmol/L) (–92.72±4.4mV,n=10 cells) compared with Con (–75.08±3.9mV,n=10 cells), P<0.001.3 Ibutilide effect on the INa recovery from inactivation curve of right ventricular myocytesWhen the pulse time is 15ms ,the INa recover 60.28% in control group ,34.52%in high-concentration group,39.28% in low-concentration group.The rate of recovery from inactivation of INa were significant slower in high-concentration of ibutilide(10-5mmol/L) and low-concentration of Ibutilide (10-6mmol/L) with that in Con, P<0.001 and P<0.05, respectively.Conclusions1 The study indicated that INa current densities in different concentration ibutilide were significant suppressed , which showed as reduction of INa current density, shift in upward direction of steady-state INa inactivation curves , and slow INa recovery rate from inactivation. These changes may underlie the altered electrical activity (decrease in the velocity and amplitude of phase 0 of action potential) and abnormal transmembrane action potentials contributing to inhabit ventricular arrhythmias .2 The study indicated that the effect of Ibutilide on the sodium ion channel activity and kinetics in different concentration group was reduced significantly, which may underlie the made electrical activity( in the velocity and amplitude of phase 0 of action potential) tend to different degree.3 The useness of Ibutilide to inhibit ventricular arrhythmias may be dependant on suppressing the sodium ion channel in phase 0 of action potential.4 The study indicates that the classⅢantiarrhythmic drug—Ibutilide has the ionchannel mechanism of inhibiting ventricular arrhythmias.In clinical practice,the drug may inhibit ventricular arrhythmias.5.Ion channels are not isolated.Defferent ion channels make the action potential,so we guess the alteration of Na+ channel will affect other ion channels,which need farther study.