Role of osmotic forces in exocytosis: studies of ADH-induced fusion in toad urinary bladder.

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Abstract
Antidiuretic hormone (ADH) treatment of toad urinary bladder activates an exocytotic-like process by which intramembrane particle aggregates are transferred from membranes of elongated cytoplasmic tubules to the luminal-facing plasma membrane. The number of these ADH-induced fusion events and the number of aggregates appearing in the luminal membrane are reduced when the luminal bathing medium is made hyperosmotic. As an apparent consequence of the inhibition of their fusion with the luminal membrane, the elongated cytoplasmic tubules swell into large, rounded vesicles. Apparently, osmotic forces are essential to the basic mechanism of exocytosis.