Guanine nucleotide-binding proteins in cultured renal epithelia_:
studies with pertussis toxin and aldosterone.
Svoboda, Sarah Sariban-Sohraby Michal, ( and Fr[acute]ed[acute]erique
Mies.
( Laboratoire de Chimie Biologique, Universit[acute]e Libre de
Bruxelles,
APStracts 5:0165F, 1998.
The GTP-binding proteins from cultured A6 epithelia were examined in
isolated membrane preparations. Binding of (35S(GTP(S revealed a
class of binding sites with an apparent Kd value of 100 nM and a Bmax
of 220 pmoles/mg protein. Short-term aldosterone treatment of the
cells did not modify the binding kinetics while PTx decreased Bmax by
50%. The mRNA levels for G(i-3, G(0, G(s, and G(q were not increased
after aldosterone. The pattern of small Mr G proteins and of PTx
-ribosylated proteins was identical in membranes of both control and
aldosterone-treated cells. Cross-linking of ((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.
Received 4 may 1998; accepted in final form 10 September 1998.
APS Manuscript Number F102-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 20 October 1998