Hypotonic regulation of mouse epithelial sodium channel in Xenopus laevis oocytes

GALIZIA L; PALMA A; MARINO G; KOTSIAS B

Tucuman

Congreso; XLI Reunión de la Sociedad argentina de Biofísica; 2012

Sociedad Argentina de Biofísica

ENaC regulation during cell swelling is relevant in cellular processes in which cell volume changes occurs, i.e. migration, proliferation, cell absorption. The sensitivity of alpha beta gamma mouse epithelial Na+ channel (mENaC) to hypotonic induced swelling was investigated in the Xenopus oocyte expression system. We used voltage clamp techniques to study the amiloride-sensitive Na+ currents (INa(amil)) and video microscopy methodologies to asses oocyte volume changes. Under conditions of mild swelling (25 % reduced hypotonicity) inward current amplitude decreased 50 % during 1.5 minutes. Time dependence analysis of current response to the voltage pulses suggest that INa(amil) is slowly inactivated during hypotonic stimuli. In contrast, there was no change in current amplitude of H2O-injected oocytes to the osmotic insult. Cytochalasin D treatment (2-5 hs, 6 µM) did not affect the observed response. However oocytes expressing a DEG mutant β-mENaC subunit (β-S518K) with an open probability of 1 showed a reduced INa(amil) hypotonicity response. Cell volume experiment indicates that the swelling amount was observed in ENaC-wt, β-S518K and water injected oocytes during hypotonic stimuli. On this basis we suggest that hypotonicity-dependent ENaC inhibition is principally mediated through an effect on open probability of channels in the membrane.