Relationship of the aldosterone-induced protein, GP70, to the conductive Na+ channel.
Although one of the primary effects of aldosterone is to increase apical membrane Na+ conductance, as yet none of the proteins induced by the hormone in renal epithelia have been shown to be related to the conductive Na+ channel. Because the toad urinary bladder aldosterone-induced glycoprotein, GP70, has recently been localized to the apical surface of this Na+ transporting epithelium, whether GP70 is associated with the Na+ channel was examined. The specificities of a monoclonal antibody used to characterize GP70 (mAb 20) and a polyclonal antibody raised against the purified bovine renal papillary Na+ channel (anti-CH) were compared: GP70 was specifically immunoprecipitated by both mAb 20 and anti-CH. Moreover, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile of mAb 20 purified toad urinary bladder membrane preparations was similar to those reported for bovine and A6 cell Na+ channels. Under nonreducing conditions, a single, very large protein was evident; reduction yielded GP70, a 140-kd polypeptide, and a number of minor bands. Interestingly, only GP70 was induced by aldosterone. Thus, GP70 appears to be associated with the toad urinary bladder conductive Na+ channel; whether GP70 is an integral subunit of the channel or whether it functions as a regulatory moiety remains to be determined. Whatever the case, because GP70 is induced by aldosterone, it likely has a central role in Na+ channel modulation.
Szerlip
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H
Department of Medicine, VA Medical Center, Philadelphia, PA 19104.
Palevsky
P
P
Cox
M
M
Blazer-Yost
B
B
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002024:Bufo marinus; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D015640:Ion Channel Gating; D008562:Membrane Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D013268:Stimulation, Chemical; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D008562:Membrane Glycoproteins; D015222:Sodium Channels; D000450:Aldosterone; D012964:Sodium