Adenylate cyclase activity in fish gills in relation to salt adaptation.
The influence of salt adaptation on specific adenylate cyclase activity (measured by conversion of [alpha-32p]-ATP into [alpha-32p]-cAMP) was investigated in gill plasma membranes of rainbow trout (Salmo gairdneri) adapted to various salinities (deionized water, DW; fresh water, FW; 3/4 sea water, 3/4 SW; sea water, SW) and in sea water adapted-mullet (Mugil sp.). Basal activity declined by a factor of 2 in trout with increasing external salinity (pmoles cAMP/mg protein/10 min: 530 in DW, 440 in FW, 340 in 3/4 SW; 250 in SW) and was very low in SW adapted-mullet: 35. The Km for ATP was similar (0.5 mM) in both FW adapted- and SW adapted- trout in either the absence (basal activity) or in the presence of stimulating agents (isoproterenol; NaF) while the Vm varied. Analysis of stimulation ratios with respect to basal levels of the enzyme showed that hormones (glucagon, VIP) and pharmacological substances (isoproterenol, NaF) display a greater potency in high salt than in low salt adapted- fish gills. In contrast, salt adaptation did not have any effect on the regulation of adenylate cyclase by PGE1. These results are interpreted in relation to the general process of osmoregulation.
D000222:Adaptation, Physiological; D000255:Adenosine Triphosphate / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D005399:Fishes / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology; D005880:Gills / Q000201:enzymology* / Q000502:physiology; D006728:Hormones / Q000494:pharmacology; D009994:Osmolar Concentration; D012969:Sodium Fluoride / Q000494:pharmacology; D014337:Trout; D014882:Water-Electrolyte Balance
D006728:Hormones; D000255:Adenosine Triphosphate; D012969:Sodium Fluoride; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases