Water and solute coupling in cells and tissues: from plant vacuoles to human epithelia.

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

Caxambu - Brasil

Conferencia; Reunião Anual da Federação de Sociedades de Biologia Experimental; 2001

Federação de Sociedades de Biologia Experimental

Water transfer and equilibrium is evidently crucial in living beings and the relatively recent discovery of spe-cific water channels (aquaporins) has given a new di­mensión to our knowledge in this field. U is now generally accepted that water con cross cell membranes by two different pathways: the lipid bilayer or specific aquaporins. More recently a third hypothetical mechanism (ion-water cotransport proteins) has been proposed to explain the solute associated water fluxes. We have explored all thes mechanisms and its regulation, going from plant (sugar beet roots) vacuoles, to isolated animal cells (mammalian ovocytes) and mammalian ephitelial cell lines cultured on permeable suports (RCCD1, T84) as well as epithelial tissues in vitro (the rat and rabbit rectum). In.all cases water movements were studied, either following volume chonges employing video microscopy (vacuoles or isolated cells) or recording transepithelial water fluxes with a specially developed experimental device (Comp Meth ond Prog in Biomedicine 53: 9-14, 1997). Molecular biology studies (mRNA injection and expression, RTPCR, in situ hybridization, western blots, cellular inmunolocalization) were employed basically to delcct aquaporins expression in different structures. The effects of different horrnonal and pharmocological agents were tested in each case and special relevance was done to the role of proton concentration in water permeability regulation From our results the following general properties of water transfer and related regulatory processes could be obtained: 1) Medium pH modifies aquoporins permeability in different strutures 2) Cell volume regulatory mechanisms are also strongly dependent on pH conditions 3) Presence of aquoporins in membranes, other than AQP2, can be hormonally regulated 4) Presence of aquoporins seems to be necessary for regulation of transepithelial, osmotically driven water fluxes and 5) Important regulated transepithelial water fluxes associated to solute transfer and observed in the absence of transephitelial osmotic or chemical gradients, can be observed in the absence of known aquaporins. These last results favor the hypothesis postulating the existence of waler-solute cotransport mecanisms.