Effects of Arginine Vasopressin and Atriopeptin on Chloride Uptake in Cultured Astroglia

Ion and water homeostasis in the CNS is subjected to a neuroendocrine control exerted by neuropeptides formed within the brain. In order to gain information on this neuroendocrine control of Cl^– homeostasis, ³⁶Cl^– uptake was measured in cultured Type-I astrocytes exposed to the neuropeptides [Arg8]Vasopressin (AVP), and atriopeptin (AP) and to various Cl^– transport modifiers. AVP increased while AP decreased ³⁶Cl^– uptake of cultured astrocytes in a dose-dependent manner. Both effects became statistically significant at greater than 10^–9 M concentration of the peptides. For the appearance of the effects at least 30-min exposure was necessary. AVP and AP extinguished each other's effect by almost stochiometric manner. When administered together with AVP, the VIA vasopressin receptor antagonist Manning compound inhibited, while V2 vasopressin receptor agonist did not influence the ³⁶Cl^– uptake-increasing effect of AVP. However, bumetanide, a specific inhibitor of Na⁺-K⁺-2Cl^– cotransport, inhibited the effect of vasopressin and also inhibited the ³⁶Cl^– uptake of AVP non-treated, control cells. Our findings suggest that brain Cl^– homeostasis is controlled by neuroendocrine system in the CNS.