| Abstract: | Rat basophilic leukemia cells (RBL-2H3) have previously been shown to contain a single type of voltage-activated channel, namely an inwardly rectifying K+ channel, under normal recording conditions. Thus, RBL-2H3 cells seemed like a logical source of mRNA for the expression cloning of inwardly rectifying K+ channels. Injection of mRNA isolated from RBL-2H3 cells into Xenopus oocytes resulted in the expression of an inward current which (1) activated at potentials negative to the K+ equilibrium potential (EK), (2)decreased in slope conductance near EK, (3) was dependent on K+]o and (4) was blocked by external Ba2+ and Cs+. These properties were similar to those of the inwardly rectifying K+ current recorded from RBL-2H3 cells using whole-cell voltage clamp. Injection of size-fractionated mRNA into Xenopus oocytes revealed that the current was most strongly expressed from the fraction containing mRNA of approximately 4–5 kb. Expression of this channel represents a starting point for the expression cloning of a novel class of K+ channels. |
