Three-dimensional organization of the aquaporin water channel: What can structure tell us about function?

Abstract

Publisher Summary The entry and exit of water across the lipid bilayer membrane is a fundamental physiological process necessary for maintaining cell homeostasis, which is crucial to the survival of an organism. The chapter discusses several observations that have been suggested in the presence of water-specific channels or pore in some tissues. These were (a) unusually high osmotic water permeability of, for instance, red blood cell membranes and renal proximal tubular epithelium, which is characterized by low Arrhenius activation energy (E a ) and is too rapid to be explained by passive diffusion of water across the bilayer, (b) reversible inhibition of the high water permeability across red blood cells by mercurial reagents, and (c) radiation inactivation studies of renal brush-border membrane vesicles and erythrocytes that indicated that a protein of ∼30kDa is responsible for the high water permeability. Additional evidence in favor of a protein responsible for water transport was provided when, upon injection of heterologous mRNAs from kidney reticulocytes and amphibian bladder into Xenopus oocytes, which is known to have low water permeability, increased water permeability was elicited.