Different homologous subunits of the amiloride-sensitive Na+ channel are differently regulated by aldosterone.
Long term regulation of the amiloride-sensitive Na+ channel activity by steroid hormones occurs via de novo protein synthesis. The messenger level of RCNaCh1, previously shown by expression cloning to be a component of this channel, was measured in colons from rats fed with a low sodium diet. After 1 week of this diet, the channel activity was increased in an all-or-none fashion, whereas the level of RCNaCh1 messenger remained constant. A cDNA coding for another subunit of the Na+ channel was obtained by polymerase chain reaction. The 650-amino acid protein, entitled RCNaCh2, is 58% homologous to RCNaCh1 and displays a similar structure. It had no intrinsic activity when expressed alone in Xenopus oocytes, but its co-expression with RCNaCh1 increased the channel activity 18 +/- 5-fold. The increase in messenger level for RCNaCh2 during the time course of the diet is likely to explain the positive regulation of the rat colon Na+ channel by steroids. Immunocytochemical localization of the RCNaCh1 subunit revealed an apical labeling in colon from sodium-depleted rats. No labeling was observed in colon from control animals. These results suggest that oligomerization is needed for the proper expression of RCNaCh1 at the cell surface.
Lingueglia
E
E
Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France.
Renard
S
S
Waldmann
R
R
Voilley
N
N
Champigny
G
G
Plass
H
H
Lazdunski
M
M
Barbry
P
P
D000450:Aldosterone / Q000502:physiology*; D000584:Amiloride / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D014981:Xenopus
D018076:DNA, Complementary; D012333:RNA, Messenger; D015222:Sodium Channels; D000450:Aldosterone; D000584:Amiloride