Electrokinetics of miniature K+ channel: Open-state V sensitivity and inhibition by K+ driving force

Kcv, isolated from a Chlorella virus, is the smallest known K+ channel. When Kcv is expressed in Xenopus oocytes and exposed to 50 mM [K+](o), its open-state current-voltage relationship (I-V) has the shape of a "tilted S'' between -200 and + 120 mV. Details of this shape depend on the conditioning voltage (Vc) immediately before an I-V recording. Unexpectedly, the I-V relationships, recorded in different [K+] o, do intersect. These characteristics are numerically described here by. ts of a kinetic model to the experimental data. In this model, the Vc sensitivity of I-V is mainly assigned to an affinity increase of external K+ association at more positive voltages. The general, tilted-S shape as well as the unexpected intersections of the I-V relationships are kinetically described by a decrease of the cord conductance by the electrochemical driving force for K+ in either direction, like in fast V-dependent blocking by competing ions.