Description of a nonselective cation current in human atrium

Ion currents were examined in isolated human atrial myocytes by using the whole-cell patch-clamp technique. When currents were recorded with a K(+)-containing pipette solution, depolarizing voltage pulses elicited a rapidly activating outward current that decayed to an apparent steady state. Exposure of cells to 10 mmol/L 4-aminopyridine markedly reduced current amplitude; however, a rapidly activating current that was approximately 30% of the steady state current amplitude remained. When pipette K+ was replaced with Cs+, a similar rapidly activating current that reversed polarity at approximately 0 mV was recorded. This current was seen in 100% of the cells tested from 17 different hearts (n = 142), and its amplitude was approximately 40% of the amplitude of the steady state current recorded in the presence of pipette K+. The current amplitude was not significantly different in cells isolated from adult (6.31 +/- 1.35 pA/pF, n = 8) and pediatric (5.54 +/- 1.04 pA/pF, n = 9) hearts. Studies designed to determine the charge-carrying species indicated that changes in bath Cl- concentration had no effect on either the amplitude or the reversal potential of this current, whereas removal of pipette Cs+ and bath Na+ dramatically reduced this current. In addition, this current was not modulated by either isoproterenol (1 mumol/L, 22 degrees C) or cell swelling. This study provides the first description of a nonselective cation current in human atrial myocytes, which may play an important role in repolarization in human atria.