GATING OF I-SK EXPRESSED IN XENOPUS-OOCYTES DEPENDS ON THE AMOUNT OF MESSENGER-RNA INJECTED

I-sK is a K+ channel of the delayed rectifier type widely distributed throughout both excitable and nonexcitable cells. Its structure is dif ferent from other cloned K+ channels and molecular details of its gati ng remain obscure. Here we show that the activation kinetics of I-sK e xpressed in xenopus oocytes depend upon the amount of its mRNA injecte d, with larger amounts resulting in slower activation kinetics with a longer initial delay during activation. Similar changes in activation kinetics occur with time after a single injection of I-sK mRNA. We pre sent two kinetic schemes which illustrate how our experimental results could arise. Both imply an interaction among individual channel prote ins during I-sK activation. The dependence of channel gating on mRNA c oncentration provides a novel mechanism for long term regulation of io n current kinetics.