ABSTRACT
This chapter deals with cellular mechanisms of the antidiuretic hormone (ADH)-induced increase in water permeability, which gives rise to the so-called hydroosmotic response, in amphibian urinary bladder. The apical plasma membrane of granular cells of amphibian urinary bladder stimulated with ADH displays numerous intramembranous particle aggregates, a structure more obviously linked to water permeability variations. The number of aggrephores is maximal in resting cells; in toad bladder, the number has been reported to be reduced by half during ADH stimulation. The chapter reviews the characteristics of the pathways for water movements and the potential biochemical correlates of some parameters whose importance has been underlined by functional and morphological studies. It describes the potential correspondence between membrane particles, microfilaments, microtubules, granules, and other characteristic ultrastructures and cAMP-controlled phosphoproteins, the chemical nature of the coat and, most of all, of the particle aggregates.
