MOLECULAR-CLONING, FUNCTIONAL EXPRESSION AND LOCALIZATION OF A NOVEL INWARD RECTIFIER POTASSIUM CHANNEL IN THE RAT-BRAIN

We have cloned a novel inward rectifier potassium channel from a rat b rain cDNA library and designated it RB-IRK2. The rat brain cDNA librar y was screened using a fragment of the mouse macrophage IRK1 cDNA as a probe. The amino acid sequence of RB-IRK2 shares 70%, 40% and 45% ide ntity to mouse IRK1, rat ROMK1 and rat GIRK1, respectively. Xenopus oo cytes injected with cRNA derived from RB-IRK2 expressed a potassium cu rrent which showed inward-rectifying channel characteristics similar t o the IRK1 current, but distinct from the ROMK1 or the GIRK1 currents. However, the localization of RB-IRK2 mRNA in rat tissues, assessed by the Northern blot analysis, differed from that of mouse IRK1. These r esults indicate that the IRK family is composed of multiple genes, whi ch express in different tissues and therefore may play heterogenous fu nctional roles in various organs, including rat central nervous system .