Small‐Conductance Calcium‐Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells

Abstract

Background Purkinje cells ( PC s) are important in cardiac arrhythmogenesis. Whether small‐conductance calcium‐activated potassium ( SK ) channels are present in PC s remains unclear. We tested the hypotheses that subtype 2 SK ( SK 2) channel proteins and apamin‐sensitive SK currents are abundantly present in PC s. Methods and Results We studied 25 normal rabbit ventricles, including 13 patch‐clamp studies, 4 for Western blotting, and 8 for immunohistochemical staining. Transmembrane action potentials were recorded in current‐clamp mode using the perforated‐patch technique. For PC s, the apamin (100 nmol/L) significantly prolonged action potential duration measured to 80% repolarization by an average of 10.4 ms (95% CI , 0.11–20.72) (n=9, P =0.047). Voltage‐clamp study showed that apamin‐sensitive SK current density was significantly larger in PC s compared with ventricular myocytes at potentials ≥0 mV. Western blotting of SK 2 expression showed that the SK 2 protein expression in the midmyocardium was 58% ( P =0.028) and the epicardium was 50% ( P =0.018) of that in the pseudotendons. Immunostaining of SK 2 protein showed that PCs stained stronger than ventricular myocytes. Confocal microscope study showed SK 2 protein was distributed to the periphery of the PC s. Conclusions SK 2 proteins are more abundantly present in the PC s than in the ventricular myocytes of normal rabbit ventricles. Apamin‐sensitive SK current is important in ventricular repolarization of normal PC s.