Vasopressin‐induced transfer via light vesicles of receptors and water channels from basolateral to apical membrane of toad bladder

Abstract

Toad bladder epithelial cells were homogenized and fractionated by Percoll density-gradient centrifugation. Binding of tritium-labeled vasopressin ([3H]AVP) was measured in surface membranes (SM), microsomes (M), and a 100,000 g (60-min) microsomal supernatant fraction (S). More than two-thirds of the total receptors were in S. Receptors in SM--but not in S--were tightly coupled to G-protein as suggested by inhibition of [3H]AVP binding by GTP. GTP-sensitivity of [3H]AVP binding was not altered by vasotocin (AVT) stimulation, although the distribution of receptors shifted from SM to S. Intact bladders, exposed on the serosal side to 1-desamino, 7-lysine-(4-azidobenzoyl), 8-arginine vasotocin (d7-N3-AVT) in the presence of UV light, exhibited a persistent hydroosmotic response compared to controls stimulated with photoaffinity analog in the dark. Cell fractions from the irradiated bladders showed a reduction in [3H]AVP binding in SM and S. Intact bladders, exposed on the mucosal side to d7-N3-AVT in the presence of UV light (while stimulated from the serosal side with AVP) exhibited a decrease in [3H]AVP binding in SM compared to controls without d7-N3-AVT.(ABSTRACT TRUNCATED AT 250 WORDS)