A LOW-NA-RNA FOR EPITHELIAL NA+ CHANNEL IN RAT RENAL INNER MEDULLA( DIET ENHANCES EXPRESSION OF MESSENGER)

The purpose of the present study was to determine whether the renal in ner medulla expresses mRNA for the rat epithelial Na+ channel (rENaC) and, if so, to define its regulatory properties using a low-Na+ diet m odel. We detected alpha, beta and gamma subunit mRNA in rat renal inne r medulla using reverse transcriptase-polymerase chain reaction (RT-PC R) with primers specific for rENaC alpha, beta and gamma subunits. Mor eover, we have developed a specific probe for the alpha subunit using RT-PCR with rENaC alpha-subunit-specific primers. The resulting cDNA w as verified by sequencing and was then used in Northern blot analysis of distal colon, whole kidney and inner medulla. The probe for the rEN aC alpha subunit hybridized not only to distal colon RNA but also to i nner medulla RNA derived from rats fed a normal diet. Furthermore, we examined the effect of a low-Na+ diet on alpha, beta and gamma subunit mRNA expression of rENaC using full-length cDNA as a probe. A marked elevation of rENaC alpha subunit mRNA abundance in the inner medulla w as observed in response to a high plasma aldosterone concentration ind uced by dietary Na+ deprivation. On the other hand, neither beta nor g amma subunit mRNA expression was enhanced by a low-Na+ diet. From thes e results, it is suggested that rENaC is responsible for Na+ transport in the renal inner medulla and that is probably regulated via transcr iptional control of the alpha subunit of ENaC.