DELAYED RECTIFICATION IN SINGLE CELLS ISOLATED FROM GUINEA-PIG SINOATRIAL NODE

We have studied delayed rectifier K+ currents (I(K)) in cells isolated from the sinoatrial node (SAN) region of the guinea pig. Using whole cell patch-clamp procedures, we measured the voltage dependence of I(K) activation and I(K) kinetics and the I(K) equilibrium potential in 4.8 mM extracellular K concentration solutions. Experiments were designed to contrast properties of guinea pig SAN I(K) with those of I(K) recorded from SAN cells of the rabbit. We find that guinea pig SAN I(K) differs from I(K) recorded from single rabbit SAN cells in its activation threshold, and in the absence of inactivation of whole cell currents recorded over a wide voltage range. These results, along with the relative insensitivity of guinea pig SAN I(K) to E-4031 and lanthanum, suggest that under our experimental conditions, a strongly rectifying I(K) component (I(K,r)) is not the major component of delayed rectification in the guinea pig SAN, as it appears to be in SAN cells of the rabbit.