Microfilaments and the hydrosmotic action of vasopressin in toad urinary bladder

The role of cytoskeletal elements in the antidiuretic hormone (ADH)-induced hydrosmotic response of the toad bladder has been investigated with the microfilament and microtubule disrupting agents, cytochalasin B and colchicine. In the presence of a transmural osmotic gradient, addition of ADH resulted in a measured osmotic permeability coefficient (Pf) of 190 +/- 12 micrometers/s; preincubation with cytochalasin B (2 x 10(-5) M) reduced this value to 138 +/- 6. However, ADH-induced diffusional permeability to tritiated water (PD) was enhanced by 17% with cytochalasin B. The toxin caused a pronounced vacuolation in granular cells only when both ADH and an osmotic gradient were present. This led to experiments with brief glutaraldehyde fixation after hormonal stimulation but before osmotic gradient imposition. Subsequent osmotic flow measurements yielded Pf values of 180 +/- 18 and 210 +/- 7 micrometers/s for ADH and ADH + cytochalasin B, respectively. With gradient imposition only after tissue fixation, no structural alterations were found. We conclude that cytochalasin B inhibition is through disruption of the intracellular portion of the pathway for osmotic flows. Comparable experimentation with colchicine indicated that its interference is primarily with ADH action on the mucosal membrane itself. These results may bear on the significance of particle aggregation in the mucosal membrane, which has been thought to indicate ADH-induced water channels but which is reported to be precluded by cytochalasin B treatment.