Single voltage-dependent and outward rectifying K+-channels in isolated rat heart cells

Studies on single K+-channel currents recorded from isolated rat heart muscle cells, in which early repolarization is known to be exceptionally fast, are reported here. A K+-channel which is blocked by TEA (tetraethylammonium) from the inside only has been found. The total open time of the channel, measured in steady-state after activation, indicated outward rectifying properties. The single channel conductance increases with depolarization from 25 pS at -70 mV to 75 pS at + 70 mV. Selectivity of the channel has also been measured and it was found that only Rb+ and K+ can permeate the channel, whereas the permeability (P) for Li+, Na+, Cl-, Mg2+, and Ca2+ is less than 0.05 times PK+. Ba2+ and CS+ block the channel activity. These results clearly demonstrate the existence of K+-selective outward rectifying conductance pathways in rat ventricular myocytes.