Time course of ADH-induced intramembranous particle aggregation in toad urinary bladder

Abstract

Freeze-fracture EM was previously used to demonstrate that intramembranous particle aggregation in granular cell luminal membrane from amphibian urinary bladder occurs in response to ADH [antidiuretic hormone] stimulation. This phenomenon appears to be a primary hormonal effect which specifically correlates with ADH-induced alterations in osmotic water permeability. To further associate this morphologic phenomenon with the action of ADH its time course was studied during ADH stimulation and the effect of brief ADH washout. The observations were related to changes induced in osmotic water permeability. In unpaired hemibladders the aggregation response is minimally evident at 2.5 min of ADH stimulation when osmotic water flow is in the process of initiation (n, 6), is probably maximized at 30 min of ADH stimulation when a high level of water flow is established (n, 6), and is dramatically diminished after 5 min of ADH washout when ADH-induced osmotic water permeability is almost completely attenuated (n, 6). These results strengthen the general hypothesis that the aggregation response to ADH is related to changes that are induced in osmotic water permeability. However, at 60 min of ADH stimulation, when osmotic water permeability is partially inhibited with respect to that at 30 min, the aggregation response in unpaired (n, 6), as well as in paired (n, 6) bladders, remains maximized. This latter observation may suggest that intrinsic inhibition of hormonally stimulated osmotic water flow across toad bladder is modulated by a mechanism that does not involve granular cell luminal membrane water permeability or that the apparent physiologic significance of the aggregation response with respect to granular cell luminal membrane function is not constant with prolonged ADH stimulation.