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

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

Caxambu, Brasil

Congreso; XVI Reuniao Anual da Federacao de Sociedades de Biologia Experimental; 2001

FeSBE

Volume changes in sugar beet root vacuoles were studied using videomicroscopy. Superfusing vacuoles in anisoosmotic conditions (modifying mannitol concentration) and also when urea partial and isoosmotically replaced mannitol, reflected a complex volume response, due to both water and solute movements. When vacuoles were preincubated in presence of HgCl2 and then a hypoosmotic challenge was applied, a HgCl2 concentration dependent reduction in the final steady state volume was observed. At 300 mM HgCl2, the volume change was reversible abolished. Volume adjustments observed in hypertonic conditions were also affected by HgCl2. The response to a hypoosmolar challenge and the osmotic response to urea, in isoosmotic conditions, were completely abolished at pH 6.6, being these effects fully reversible. These results can be interpreted accepting that 1) mercury sensitive water channels, present in the studied structure, are blocked by low pH; 2) urea and in same cases mannitol reflection coefficients (s) were also modified. Unexpectedly, water permeability was apparently not affected by medium acidification in “hyperosmotic” experiments, while solute (mannitol s) would be reduced. It is concluded that proton concentration differently affects water and solute permeability during hyposmotic or hyperosmotic challenges.