ISOLATION OF A RAT AMILORIDE-BINDING PROTEIN CDNA CLONE - TISSUE DISTRIBUTION AND REGULATION OF EXPRESSION

Sodium transport across high resistance epithelia involves bath an api cal amiloride-sensitive sodium channel and the basal Na+-K+-ATPase pum p. Aldosterone regulates sodium transport by increasing the sodium per meability of the sodium channels. To study further the regulation of g ene expression in sodium-transporting epithelia by corticosteroids, we have cloned an amiloride-binding protein (ABP) cDNA from rat descendi ng colon and kidney. Identical 311 nucleotide cDNAs were amplified fro m both rat descending colon and kidney, and the predicted amino acid s equence exhibited 83% homology to the equivalent region of the human p eptide sequence. Use of this cDNA as a probe resulted in detection of a transcript in both the small and large bowel, thymus, and seminal ve sicle. The latter tissue exhibited the highest level of rat ABP expres sion. Low to undetectable levels of rat ABP were expressed in the desc ending colon and kidney. No regulation of rat ABP by either class of c orticosteroids was observed. Levels of ABP were low at birth and incre ased gradually to adult levels just before weaning in the bowel. The d istribution of rat ABP is not as would be predicted for an aldosterone -induced gene and is thus unlikely to be a component of the amiloride- sensitive electrogenic sodium channel.