Potassium currents in isolated human atrial and ventricular cardiocytes

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Abstract
The whole‐cell configuration of the patch‐clamp technique was applied to study and compare ion currents in single ventricular and atrial cardiocytes isolated from human myocardium. In ventricular cardiocytes the K+ inward rectifier current (IK1) was three times larger than in atrial cardiocytes, while its inactivation kinetics were twice as slow when measured at ‐140 mV. The magnitude of these variables depended on the test potential but was independent of changes in holding potential. A transient outward current (Ito) was observed in both ventricular and atrial cardiocytes. The amplitude of the inactivating component of Ito was not significantly different in atrial and ventricular cells, but the time course of inactivation was significantly longer in atrial than in ventricular cardiocytes. Steady‐state inactivation of Ito in atrial cells was well described by a two‐state Boltzmann function having a midpoint potential of ‐ 41.4mV and a slope factor of 6.9 mV‐1. No discernible K+ delayed rectifier current (IK) was observed in either cell type. In four of the 12 atrial cells studied, a time dependent inward current was observed at negative test potentials having a 240 ± 21 ms time constant for activation and an amplitude of 101±28pA. This current, which resembled the pacemaker current (It), was not observed in any of the ventricular cells examined.