Membrane tension modulates the effects of apical cholesterol on the renal epithelial sodium channel.

We used patch-clamp techniques and A6 distal nephron cells as a model to determine how cholesterol regulates the renal epithelial sodium channel (ENaC). We found that luminal methyl-beta-cyclodextrin (mbetaCD, a cholesterol scavenger) did not acutely affect ENaC activity at a previously used concentration of 10 mM: but significantly decreased ENaC activity both when the cell membrane was stretched and at a higher concentration of 50 mM: Luminal cholesterol had no effect on ENaC activity at a concentration of 50 microg/ml but significantly increased ENaC activity both when the cell membrane was stretched and at a higher concentration of 200 microg/ml. Confocal microscopy data indicate that membrane tension facilitates both mbetaCD extraction of cholesterol and A6 cell uptake of exogenous cholesterol. Together with previous findings that cholesterol in the apical membrane is tightly packed with sphingolipids and that stretch can affect lipid distribution, our data suggest that membrane tension modulates the effects of mbetaCD and cholesterol on ENaC activity, probably by facilitating both extraction and enrichment of apical cholesterol.