Arginine-vasopressin (AVP) has been proposed to be involved in the modulation of acid-base transporters; however, the nature of the mechanisms underlying AVP direct action on intracellular pH (pHi) in the cortical collecting duct (CCD) is not yet clearly defined. The aim of the present study was to elucidate which are the proteins implicated in AVP modulation of pHi, as well as the receptors involved in these responses using a CCD cell line (RCCD1); pHi was monitored with the fluorescent dye BCECF in basal conditions and after stimulation with basolateral 10-8 M AVP. Specific V1- or V2-receptor antagonists were also used. RT-PCR studies demonstrated that RCCD1 cells express V1a and V2 receptors. Functional studies showed that while V2-receptor activation induced a biphasic response (alkalinization-acidification), V1-receptor activation resulted in an intracellular acidification. The V2-mediated alkalinization phase involves the activation of basolateral NHE-1 isoform of the Na+/H+ exchanger while in the acidification phase CFTR is probably implicated. On the other hand, V1-mediated acidification was due to activation of a Cl-/HCO3- exchanger. We conclude that in RCCD1 cells AVP selectively activates, via a complex of V1 and V2 receptor-mediated actions, different ion transporters linked to pHi regulation which might have physiological implications.

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