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In abdominal skins of toads (Bufo marinus) challenged with either vasopressin or isoproterenol, the stimulation of transepithelial water flow was accompanied by the appearance of intramembrane particle (IMP) aggregates. These aggregates were found only in the apical plasma membrane of granular cells of the first-reacting cell layer. The effect of vasopressin varied in magnitude and could be selectively blocked by preincubation of the skins with methohexital. This barbiturate also prevented the appearance of IMP aggregates. Preexposure with propranolol had a similar effect in skins challenged with isoproterenol. Linear regression analysis of net water flow vs. the percentage surface occupied by IMP aggregates showed a significant (P less than 0.001) correlation, which applied to data obtained in six different experimental conditions, i.e., vasopressin or isoproterenol alone and either of these agents in combination with methohexital or propranolol. The results reported here in a nonurinary epithelium (toad epidermis) suggest that the appearance of IMP aggregates is a general response in epithelia undergoing adenosine 3',5'-cyclic monophosphate-mediated changes in water permeability.

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