Time dependent changes in biophysical properties of minK channels expressed in Xenopus oocytes

Slowly activating, voltage-dependent minK channels cloned from rat kidney were expressed in Xenopus oocytes. The maximal conductance (gmax) through these channels increased from 11 microS at day two after mRNA injection to 22 microS after one week. This increase of gmax is presumably the result of an increase in the number of functional channels through protein synthesis of the oocyte. Concurrent with the increase of gmax the voltage needed to evoke a half-maximal conductance (V1/2) was shifted to more negative potentials, while the activation of minK channels was accelerated. These results suggest a relation between protein density and activation of minK channels. Twofold changes of gmax were also observed in oocytes expressing the Shaker related rat potassium channel RBK1; however, there was no relation between gmax, V1/2 and the activation kinetics of RBK1. These results are consistent with the hypothesis that minK channel-formation and activation might involve subunit assembly.