Energize Animal Plasma Membranes for Secretion and Absorption of Ions and Fluids '

SYNOPSIS. H + V-ATPases are well known energizers of endomembranes; thus they play a key role in the acidification of vacuoles and vesicles. More recently it has become clear that they energize many plasma membranes as well. In epithelial cells H + V-ATPases usually energize apical plasma membranes in the same sense that Na + /K + P-ATPases usually energize basolateral plasma membranes. Examples of four fundamental processes so energized will be reviewed—Na + and Cl~ absorption by the frog skin, K + secretion by the caterpillar midgut, fluid secretion by insect Malpighian tubules, and fluid absorption by insect ovarian follicle cells. It is likely that apical membranes of fresh water fish and other animals that live in media in which the concentration of Na + is low, are also energized by H + V-ATPases.