Characterization of maintained voltage-dependent K+-channels induced in Xenopus oocytes by rat brain mRNA

Abstract The voltage-dependent K + currents encoded by rat brain mRNA were studied in Xenopus oocytes after the voltage-dependent Na + currents and the Ca 2+ -activated Cl − currents were eliminated pharmacologically. This paper describes the maintained K + currents ( I K ), defined primarily by resistance to inactivation for 1 s at a holding potential of −40 mV. I K activates at potentials more positive than −60 to −70 mV and consists of both low-threshold and high-threshold components. I K is partially blocked by both tetraethyl ammonium (TEA) and 4-aminopyridine (4-AP), which appear to be blocking the same component. Long depolarizing pulses result in incomplete inactivation of I K ; the inactivating component is inhibited by TEA. Sucrose density gradient fractionation partially resolves the RNA encoding the several components of I K ; most I K arises from size classes between 3.8 and 9.5 kb. The study gives further evidence for the existence of numerous distinct RNA populations that encode brain K + channels different from previously reported cloned K + channels that have been expressed in Xenopus oocytes.