Guanine nucleotide binding proteins in cultured renal epithelia: studies with pertussis toxin and aldosterone
Sariban-Sohraby, S.; Svoboda, M.; Mies, F.
American Journal of Physiology 276(1): F10-F17
1999
ISSN/ISBN: 0002-9513 PMID: 9887075 Document Number: 506460
The GTP-binding proteins from cultured A6 epithelia were examined in isolated membrane preparations. Binding of [35S]GTPcS revealed a class of binding sites with an apparent Kd value of 100 nM and a Bmax of 220 pmol/mg protein. Short-term aldosterone treatment of the cells did not modify the binding kinetics, whereas pertussis toxin (PTX) decreased Bmax by 50%. The mRNA levels for Gai-3, Ga0, Gas, and Gaq were not increased after aldosterone. The patterns of small Mr G proteins and of PTX-ribosylated proteins were identical in membranes of both control and aldosterone-treated cells. Cross-linking of [a-32P]GTP, in control membranes, showed either no labeling or a faint band of Mr 59.5 kDa. This protein became prominent after aldosterone, and its labeling decreased with spironolactone. Thus short-term aldosterone does not promote increased expression of known heterotrimeric G proteins in epithelial membranes but activates resident PTX-sensitive Gi proteins and stimulates the expression of a specific GTP-binding protein of Mr 59.5 kDa. Reprinted by permission of the publisher.