Effects of vasopressin on epithelial transport

Vasopressin increases the permeability of responsive epithelia for a variety of chemical species, such as sodium, urea, water, and lipophilic molecules. The analysis of the mechanisms leading to the stimulation of water transport (hydrosmotic action) is the main topic of this review. A model implying the quantal insertion of water channels into the apical epithelial membrane by an exocytosislike process is discussed with reference to biophysical, biochemical, and ultrastructural results obtained in the past few years. It is also shown that, in nonexcitable cells, insertion of transport units packed in intracytoplasmic structures may be a rather general mechanism for controlling membrane transport rates.