The occurrence of stable subconductance levels in Na(+)-activated K+ channels in excised membrane patches from guinea-pig ventricular myocytes.

Twelve short-lived subconductance levels have been recognized in potassium channels activated by intracellular Na+ (KNa channels) in membrane patches excised from guinea-pig ventricular myocytes. When stable recording was achieved over a prolonged period (> 30 min), sojourns of opening to one of two stable subconductance levels (approximately 30 and 70% of the main-state level) occurred spontaneously. These periods of activity showed similar kinetics (open and closed time distributions) to those of openings to the main-state conductance. Opening to transient sublevels was still detected during openings of the channel to the stable sublevels. These results suggest that the KNa channel has a complex oligomeric structure, in which twelve separate pores would seem to be functionally organized into either three or four domains that show a high degree of co-operativity in their gating.