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Am J Physiol Renal Physiol 256: F965-F969, 1989;
0363-6127/89 $5.00
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AJP - Renal Physiology, Vol 256, Issue 5 965-F969, Copyright © 1989 by American Physiological Society

ARTICLES

Guanosine nucleotide-dependent activation of the amiloride-blockable Na+ channel

H. Garty, O. Yeger, A. Yanovsky and C. Asher
Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel.

Effects of guanosine nucleotides on the epithelial Na+ channel were studied in apical membrane vesicles derived from the toad bladder epithelium. Trapping 10 microM guanosine-5'-O-(thiotriphosphate) (GTP gamma S) in vesicles evoked two- to fourfold increase in the amiloride-sensitive (Na+ channel-mediated) 22Na+ uptake. The nucleotide had no significant effect on the amiloride-insensitive 22Na+ uptake or the valinomycin-mediated 86Rb+ uptake in the same membranes. The stimulatory action of GTP gamma S was mimicked by 5'-guanylylimidiodiphosphate (GppNHp) and could at least partly be reversed by guanosine-5'-O-(thiodiphosphate) (GDP beta S) (10-fold excess). GTP itself and adenosine-5'-O-(thiotriphosphate) (ATP gamma S) had no sustained effect on Na+ transport in vesicles. Thus it appears that the epithelial Na+ channel is directly or indirectly regulated by the occupancy of a guanosine-specific site, probably the alpha subunit of a G protein. The possibility that GTP gamma S acts indirectly by activating a membrane-bound, GTP-dependent enzyme the product of which modulates the channel conductance was assessed by measuring 22Na+ fluxes in membrane vesicles prepared to contain products of such enzymes. None of the reagents tested [adenosine 3',5' cyclic monophosphate (cAMP), guanosine 3',5' cyclic monophosphate (cGMP), inositol 1,4,5-trisphosphate (IP3), and diacylglycerol (DAG)] increased the tracer flux in vesicles or altered its response to GTP gamma S.


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S. Sariban-Sohraby, M. Svoboda, and F. Mies
Guanine nucleotide binding proteins in cultured renal epithelia: studies with pertussis toxin and aldosterone
Am J Physiol Renal Physiol, January 1, 1999; 276(1): F10 - F17.
[Abstract] [Full Text] [PDF]


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