POTASSIUM CURRENTS IN ISOLATED HUMAN ATRIAL AND VENTRICULAR CARDIOCYTES

The whole-cell configuration of the patch-clamp technique was applied to study and compare ion currents in single ventricular and atrial car diocytes isolated from human myocardium. In ventricular cardiocytes th e K+ inward rectifier current (I(K1)) was three times larger than in a trial cardiocytes, while its inactivation kinetics were twice as slow when measured at - 140 mV. The magnitude of these variables depended o n the test potential but was independent of changes in holding potenti al. A transient outward current (I(to)) was observed in both ventricul ar and atrial cardiocytes. The amplitude of the inactivating component of I(to) was not significantly different in atrial and ventricular ce lls, but the time course of inactivation was significantly longer in a trial than in ventricular cardiocytes. Steady-state inactivation of I( to) in atrial cells was well described by a two-state Boltzmann functi on having a midpoint potential of -41.4 mV and a slope factor of 6.9 m V-1. No discernible K+ delayed rectifier current (I(K)) was observed i n either cell type. In four of the 12 atrial cells studied, a time dep endent inward current was observed at negative test potentials having a 240 +/- 21 ms time constant for activation and an amplitude of 101 /- 28 pA. This current, which resembled the pacemaker current (I(f)), was not observed in any of the ventricular cells examined.