Two types of delayed rectifying K+ channels in atrial cells of guinea pig heart

Whole-cell clamp experiments revealed the double exponential deactivation of the delayed rectifier K+ current in single guinea pig atrial myocytes. Two types of K(+)-selective channels were identified by applying repolarizing voltage pulses to cell-free patches from atrial cell membrane, where inward-rectifier, ATP-sensitive, and muscarinic K+ channels were all inactivated. Under a symmetrical 150 mM K+ condition, single channel conductances of the channels were 10 and 3 pS. The reversal potential obtained from the unitary current-voltage relation coincided with the equilibrium potential for K+. Ensemble averages of both types of single channel currents showed deactivation kinetics upon hyperpolarizing to potentials between -40 and -120 mV. The more positive the pre-pulse potential, the greater was the peak ensemble current. It is concluded that these two channels are responsible for atrial delayed rectifying K+ currents.