Properties of potassium currents in Purkinje cells of failing human hearts

Cardiac Purkinje fibers play an important role in cardiac arrhythmias, but no information is available about ionic currents in human cardiac Purkinje cells (PCs). PCs and midmyocardial ventricular myocytes (VMs) were isolated from explanted human hearts. K+ currents were evaluated at 37degreesC with whole cell patch clamp. PCs had clear inward rectifier K+ current (I-K1), with a density not significantly different from VMs between -110 and -20 mV. A Cs+-sensitive, time-dependent hyperpolarization-activated current was measurable negative to -60 mV. Transient outward current (I-to) density was smaller, but end pulse sustained current (I-sus) was larger, in PCs vs. VMs. I-to recovery was substantially slower in PCs, leading to strong frequency dependence. Unlike VM I-to, which was unaffected by 10 mM tetraethylammonium, Purkinje I-to was strongly inhibited by tetraethylammonium, and Purkinje I-to was 10-fold more sensitive to 4-aminopyridine than VM. PC I-sus was also reduced strongly by 10 mM tetraethylammonium. In conclusion, human PCs demonstrate a prominent I-K1, a time-dependent hyperpolarization-activated current, and an I-to with pharmacological sensitivity and recovery kinetics different from those in the atrium or ventricle and compatible with a different molecular basis.