Intracellular sodium concentration can regulate epithelial sodium channel (ENaC) sensitivity to osmotic stimuli

MARINO, G; PALMA, A; GALIZIA L; KOTSIAS, BA

San Miguel deTucumán

Congreso; III LAFeBS, IX IberoAmerican Congress of Biophysics, XLV Reunion Anual SAB 2016; 2016

Sociedad Argentina de Biofísica

Epithelial sodium channel (ENaC) belongs to a protein family which includes mechanoreceptors which possesses a mechanical signal-translating function. Among other factors, ENaC function is affected by changes of the intracellular sodium concentration, in a process called feedback inhibition, which is dependent of ENaC intracellular C-terminal regions and affects open probability (Po) and number of channels. Although its osmosensitivityis a controversial issue we previouslyinvestigated ENaC response to mild hypotonic stimuli in the Xenopus oocytes expression system.On this basis we suggested that mild hypotonicity(25 %) causes an ENaC inhibition that is principally mediated through an effect on the open probability of channels in the membrane (Galizia et al, 2013). As ENaC activity is regulated by intracellular sodium, we then attempted to study the possible its role in the hypotonic dependent inhibition of ENaC. Our recent resultssuggest that hypotonicity-dependent ENaCinhibition,could be mediated by an intracellular sodium dependent mechanism, involving a voltage dependent effect.In order to continue the study on the role of intracellular sodium on the ENaC regulation mediated by osmotic challenges we used the voltage clamp technique with the injection of the three subunits of the mouse ENaC (mENaC)to measure the amiloride-sensitive Na+ currents (INa(amil)).. We performed experiments increasing the osmotic gradientsapplied.Results indicates thatat low intracellular sodium conditions(20 mM) the inhibition of the inward Ina(amil) is dependent on the osmotic gradient magnitude (33 % hypotonicity).In addition in order to evaluate if the sodium dependent sodium regulation of ENaC by osmotic stimuli could be reverted by increasing sodium rapidlywe performed experiments of acute sodium load during 5 minutes and we measure the INa(amil) in response to hypotonic stimuli. Results suggest that although intracellular sodium can modify the ENaC sensitivity to osmotic stimuli, a rapid increase in intracellular sodium is not an enough condition to elicit the hypotonic ENaC inhibition.This opens the possibility of a crucialrole of long term effects of intracellular sodium increase on ENaC osmotic sensitivity.ReferencesGalizia et al J Membr Biol. 2013. 246 P 949.