Aldosterone-induced glycoproteins: electrophysiological-biochemical correlation.
Aldosterone induces the synthesis of a group of glycoproteins (GP65,70) in toad urinary bladders which are potential effectors of the natriferic action of this hormone. In the present study we have confirmed that aldosterone produces a two-phase electrophysiological response. During the early phase (less than 3 h) short-circuit current and transepithelial conductance increase in parallel, while during the late phase (greater than 3 h) short-circuit current continues to increase without any further change in conductance. By biosynthetically labeling aldosterone-treated toad bladders with [35S]methionine either during the early (h 0-2 or 1-3) or the late (h 4-6 or 7-9) phases of the natriferic response, we have demonstrated that GP65,70 is synthesized as a late effect of aldosterone. Since synthesis of GP65,70 occurs at a time when the electromotive force of the Na+ pump is increasing, and since GP65,70 biochemically resembles the beta subunit of Na+/K+-ATPase, studies were undertaken to examine whether GP65,70 is the beta subunit. Purified amphibian renal beta subunit was analyzed by two-dimensional polyacrylamide gel electrophoresis and was found to have an isoelectric point and Mr value similar to those of GP65,70. However, when nitrocellulose blots containing wheat germ agglutinin-purified proteins from aldosterone-treated bladders were stained with monospecific polyclonal antibodies developed against the beta subunit, GP65,70 was not recognized, whereas a group of slightly more acidic proteins of similar Mr were recognized. Thus, GP65,70 is not the beta subunit of Na+/Ka+-ATPase. Further studies are needed to determine the cellular function of GP65,70.
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H M
HM
Renal-Electrolyte Section, Veterans Administration Medical Center, Philadelphia, PA 19104.
Weisberg
L
L
Geering
K
K
Rossier
B C
BC
Cox
M
M
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D002024:Bufo marinus; D002846:Chromatography, Affinity; D004553:Electric Conductivity; D004790:Enzyme Induction; D004848:Epithelium / Q000502:physiology; D066298:In Vitro Techniques; D007700:Kinetics; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000302:isolation & purification; D008715:Methionine / Q000378:metabolism; D008970:Molecular Weight; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*; D013462:Sulfur Radioisotopes; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D013462:Sulfur Radioisotopes; D000450:Aldosterone; D008715:Methionine; D000254:Sodium-Potassium-Exchanging ATPase