VASOPRESSIN INHIBITS CALCIUM-COUPLED SODIUM-EFFLUX SYSTEM IN RAT-BRAIN

Centrally released vasopressin plays an important role in the regulati on of brain water and electrolyte composition and can affect brain int racellular pH and ATP synthesis in vivo. In this study, we evaluated t he effects of [Arg(8)]vasopressin (AVP) on the Na+-Ca2+ exchanger, an important pathway in the regulation of cell Ca2+ concentration. It was found that AVP inhibited the Na+-Ca2+ exchanger in rat brain synaptos omes. This effect was completely blocked by the vasopressin V-1-recept or antagonist d(CH2)(5)[(O-Me) Tyr(2), Arg(8)]vasopressin. In addition , the vasopressin V-2-receptor agonist 1-desamino-8-D-arginine vasopre ssin had no effect on the Na+-Ca2+ exchanger in rat brain synaptosomes . Depletion of intracellular Ca2+ by caffeine also had no effect on th e effect of AVP on the Na+-Ca2+ exchanger. Na+ uptake by other pathway s was also evaluated. It was found that AVP had no effect on Na+ uptak e by pathways other than the Na+-Ca2+ exchanger. It is concluded that AVP inhibits the Na+-Ca2+ exchanger in neuronal membranes through vaso pressin V-1 receptors. Since this pathway is important in the regulati on of cell volume and cytosolic Ca2+ in excitable tissue, AVP may impa ir neuronal cell repolarization in the central nervous system.