A1 Adenosine Receptor Modulation of Adenylyl Cyclase of a Deep-living Teleost Fish, Antimora rostrata.

Low temperatures and high hydrostatic pressures are typical of the deep sea. The effects of these parameters on transmembrane signal transduction were determined through a study of the A1 adenosine receptor-inhibitory guanine nucleotide binding protein-adenylyl cyclase system in brain membranes of the bathyal teleost fish, Antimora rostrata (Moridae). The components of this system were analyzed at 5°C and 1 atm, and the role of the A1 receptor in the modulation of adenylyl cyclase was determined. The A1 selective radioligand N6-[3H]cyclohexyladenosine bound saturably, reversibly, and with high affinity. The Kd of N6-[3H]cyclohexyladenosine estimated from kinetic measurements was 1.11 nM; the Kd determined from equilibrium binding was 4.86 nM. [32P]ADP-ribosylation of brain membranes by pertussis toxin labeled substrates with apparent molecular masses of 39,000 to 41,000 Da. Basal adenylyl cyclase activity was inhibited in a concentration-dependent manner by the A1 adenosine receptor agonist N6-cyclopentyladenosine (IC50 = 5.08 μM). The inhibition of adenylyl cyclase activity was dependent upon GTP. Basal adenylyl cyclase activity was unaffected by 272 atm of pressure. The efficacy of 100 μM N6-cyclopentyladenosine as an inhibitor of adenylyl cyclase was the same at atmospheric pressure and at 272 atm. The inhibition of adenylyl cyclase by the agonist 5'-N-ethylcarboxamidoadenosine (100 μM) at 272 atm was twice that observed at atmospheric pressure. Although consideration of the effects of low temperature and high hydrostatic pressure on acyl chain order suggest that deep-sea conditions will perturb membrane function, signal transduction by the A1 receptor system of the bathyal fish A. rostrata is not disrupted by deep-sea conditions.