Biophysical properties of epithelial water channels

MARIO PARISI; GABRIELA AMODEO; CLAUDIA CAPURRO; RICARDO DORR; PAULA FORD; ROXANA TORIANO

BIOPHYSICAL CHEMISTRY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1997 vol. 68 p. 255 - 263

0301-4622

The biophysical models describing the structure of water pores or channels have evolved, during the last forty years, froma pure ?black box? approach to a molecular based proposal. The initial ?sieving pore? in which water and other moleculeswere moving together was replaced by a more restrictive model, where water is moving alone in a ?single file? mode.Aquaporins discovery and cloning [G.M. Preston, T.P. Carroll, W.B. Guggino, P. Agre, Science 256 (1992) 3651 leaded tothe ?hour-glass model? and other alternative proposals, combining information coming from molecular biology experimentsand two dimensional crystallography. Concerning water transfers in epithelial barriers the problem is quite complex, becausethere are at least two alternative pathways: paracellular and transcellular and three different driving forces: hydrostaticpressure, osmotic pressure or ?transport coupled? movements. In the case of ADH-sensitive epithelia it is more or lessaccepted that regulated water channels (AQP2), that can be inserted in the apical membrane, coexist with basolateral residentwater channels (AQP3). The mechanism underlying the so-called ?transport associated water transfer? is still controversial.From the classical standing gradient model to the ion-water co-transport, different hypothesis are under consideration.Coming back to hormonal regulations, other than the well-known regulation by neuro-hypophysis peptides, a steroid secondmessenger, progesterone, has been recently proposed [P. Ford, G. Amodeo, C. Capurro, C. Ibarra, R. Dorr, P. Ripoche, M.Parisi, Am. 3. Physiol. 270 (1996) F880]. 0 1997 Elsevier Science B.V.