Water permeability studies in cultured cells.

TORIANO, ROXANA; FORD, PAULA; RIVAROLA, VALERIA; PARISI, MARIO

Buenos Aires - Argentina

Congreso; III Congreso Iberoamericano de Biofísica.; 1997

Three driving forces can induce net water movements (Jw) across an epithelial harrier: 1) an osmotic gradient (DP); 2) a hydrostatic gradient (DP) and 3) a solute coupied transfer. The observed Jw can proceed either through a transcellular or a paracellular route.Three different cell lines were studied to compare the behavior of water movements in different models: LLC-PK1 transfected with aquaporin 2 (AQP2), a specific water channel vassopresin modulated); MDCK, originated from a tight epithelium and T84 that derive from a leaky epithelium. These cells form an epithelial barrier on permeablc supports. Jw and mannitol permeability (Ps) were studied simultaneously in AQP2 transfected cells. A clear and reversible increase in Jw under vassopresin (26 nM) plus forskolin (10 mM), in the presence of an osmotic gradient (12.5 mM mannitol in the serosal side), was observed (Jw = -0.37 ± 0.06 ul.min-1 before and Jw =- 1.37 ± 0.09 ul.min-1 after gradient, n = 6, p < 0.001). This hydrosmotic response was inhibited by 0.3 mM HgCl2 (an inhibitor of water channels). that reduced the osmotic permeability an 80%, and uncoupled with Ps.((3.22 ± 0.82). 10-6cm.s-1 , n=6). These results indicated a transcellular water pathway. without changes in the paracellular pathway. No aquaporins had been detected for MDCK and T84 cells. Cells showed a basal secretory Jw in the absence oí any transepithelial gradient. MDCK cells, expose lo an osmotic gradient, reverted their secretory Jw (-1.26 ± 0.27 (ul.min-1 ) to an absorptive one which is associated with a diffusion potential (DV -1.5  ± 0.3 mV before and -8.4 ± 0.7 mV after gradient) Because of the spontaneous behavior of MDCK and T84 under such conditions these cells are specially appropriate to study the transepithelial ion associated water movements.