Two distinct K+ channels in lamprey (Lampetra fluviatilis) erythrocyte membrane characterized by single channel patch...

Two channels, distinguished by using single-channel patch-clamp, carry out potassium transport across the red cell membrane of lamprey erythrocytes. A small-conductance, inwardly rectifying K(+)-selective channel was observed in both isotonic and hypotonic solutions (osmolarity decreased by 50%). The single-channel conductance was 26 +/- 3 pS in isotonic (132 mM K+) solutions and 24 +/- 2 pS in hypotonic (63 mM K+) solutions. No outward conductance was found for this channel, and the channel activity was completely inhibited by barium. Cell swelling activated another inwardly rectifying K+ channel with a larger inward conductance of 65 pS and outward conductance of 15 pS in the on-cell configuration. In this channel, rectification was due to the block of outward currents by Mg2+ and Ca2+ ions, since when both ions were removed from the cytosolic side in inside-out patches the conductance of the channel was nearly ohmic. In contrast to the small-conductance channel, the swelling-activated channel was observed also in the presence of barium in the pipette. Neither type of channel was dependent on the presence of Ca2+ ions on the cytosolic side for activity.