Hydrostatic pressure alters the time course of GTP[S] binding to G proteins in brain membranes from two congeneric marine fishes

The effects of hydrostatic pressure on the receptor-stimulated exchange of guanosine triphosphate (GTP) for guanosine diphosphate (GDP) on the alpha s ubunit of G proteins were studied in two congeneric marine teleost fishes t hat differ in their depths of distribution. The poorly hydrolyzable GTP ana log [S-35]guanosine 5'-[gamma-thio]triphosphate ([S-35]GTP[S]) was used to monitor the modulation of signal transduction by the A(1) adenosine recepto r agonist N-6-R-(phenylisopropyl)adenosine (R-PIA) in brain membranes of th e scorpaenids Sebastolobus alascanus and S. altivelis. The maximal binding (B-max) and dissociation constant (K-d) values, determined from equilibrium binding isotherms at atmospheric pressure (5 degrees C), were similar in t he two species. The B-max values for these species are much lower than lite rature values for mammalian brain tissue (25 degrees C); however, the K-d v alues of the teleost and mammalian G proteins are similar. The EC50 values for the A(1) adenosine receptor agonist R-PIA were similar in the two speci es. Hydrostatic pressure of 204 atm altered the binding of [S-35]GTP[S]; ba sal [S-35]GTP[S] binding decreased 25%. The A(1) adenosine receptor agonist R-PIA and the muscarinic cholinergic receptor agonist carbamyl choline sti mulated [S-35]GTP[S] binding at 1 and 204 atm. At atmospheric pressure the half-time (t(1/2)) of [S-35]GTP[S] binding differed between the two species . The GTP[S] on rate (k(on)) is larger in the shallower-living S. alascanus . Increased hydrostatic pressure altered the time course, decreasing the t( 1/2) in both species. The pressures that elicit this change in the time cou rse differ between the species. However, interpolating over the range of in situ pressures the species experience, the values are similar in the two s pecies. The guanyl nucleotide binding properties of the G protein a subunit s appear to be conserved at the environmental temperatures and pressures th e species experience.