Effects of Na+ on the predominant K+ channel in the tonoplast of Chara: Decrease of conductance by blocks in 100 nanosecond range and induction of oligo- or poly-subconductance gating modes

Abstract

We present three mechanisms by which Na+ inhibits the open channel cut-rents of the predominant K+ channel in the tonoplast of Chara corallina: (i) Fast block, i.e., short (100 ns range) interruptions of the open channel current which are determined by open channel noise analysis, (ii): Oligo-subconductance mode, i.e., a gating mode which occurs preferentially in the presence of Na+; this mode comprises a discrete number (here 3) of open states with smaller conductances than normal, and (iii): Polysubconductance mode, i.e., a gating mode with a nondiscrete, large number (>30) of states with smaller conductances than the main open channel conductance. This novel mode has also been observed only in the presence of Na+.