Water Permeability studies in cells and tissues

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

Paris - Francia

Conferencia; Molecular Phyiology of Water Transport; 1997

Three different mechanisms are associated to the movement of water across biological membranes: 1) A net water movement (Jw) is driven by a gradient of hydrostatic pressure (D P); 2) The observed Jw is generated by an osmotic gradient (D P ) and 3) The Jw is associated to an ionic transport and can be observed in the absence of any "external" D P or D P. Water movements in isolated cells give crucial information to understand the more complex situations observed in animal an plant tissues. Isolated cells: We studied the rat oocyte, searching for a specific water pathway. Volume changes, induced by an osmotic gradient, were followed by video-microscopy. Proestro oocytes osmotic (Posm) permeability was sensitive to HgCI2 and the inhibitory effect was reversed by mercaptoethanol. Estro oocytes had a reduced Posm and lost its sensitivity to mercurials. Proestro oocytes spontaneously evolved, in 18 hours to estro conditions. it is concluded that an specific water pathway is lost during the oocyte arrival to maturity. Animal tissues: We studied different cell lines (Caco2, T84, LLC-PK1, MDCK) that form epithelial barriers on permeable supports. These models are specially appropriated to study the "ion transport associated water movements". No aquaporin has been described in these celis. Nevertheless, and specialiy in the case of MDCK, an important net water flux (Jw) was observed in the absence of any transepithelial gradient This was a secretory Jw, and when the mucosal bath tonicity was reduced (creating an osmotic gradient) the Jw reverted to an absorptive one, associated to a diffusion potentiaL It is concluded that alternative mechanisms to aquaporin-mediated transfer (water-solute co-transport?) can be underlying the observed results. Plant tissues: Hydrostatic pressure (or tensión) gradients (D P) are classically associated to water movements in plant tissues. We have studied the vectorial movements of water in the root of the sugar beet (Beta vulgaris). Transversal and longitudinal osmotic and hydrostatic gradients were applied. It was observed that the D P driven longitudinal movement would be easier in the root-to-leaves direction. This is a novel result, indicating vectorial directionality to the D P driven water movements in plant tissues.