MOLECULAR-CLONING AND FUNCTIONAL EXPRESSION OF A NOVEL BRAIN-SPECIFICINWARD RECTIFIER POTASSIUM CHANNEL

We have cloned a novel brain-specific inward rectifier K+ channel from a mouse brain cDNA library and designated it MB-IRK3. The mouse brain cDNA library was screened using a fragment of the mouse macrophage in ward rectifier K+ channel (IRK1) cDNA as a probe. The amino acid seque nce of MB-IRK3 shares 61% and 64% identity to MB-IRK1 and RB-IRK2, res pectively. Xenopus oocytes injected with cRNA derived from this clone expressed a potassium current which showed inward-rectifying channel c haracteristics similar to MB-IRK1 and RB-IRK2 currents, but distinct f rom ROMK1 or GIRK1 current. However, the single channel conductance of MB-IRK3 was similar to 10 pS with 140 mM extracellular K+, which was distinct from that of MB-IRK1 (20 pS). MB-IRK3 mRNA expressed specific ally in the forebrain, which clearly differed from MB-IRK1 and RB-IRK2 mRNAs. These results indicate that members of the IRK family with dis tinct electrophysiological properties express differentially and may p lay heterogenous functional roles in brain functions.