Role for cholesterol and caveolin‐rich membrane microdomains in controlling the activity Na+/H+ exchange 1 independently of mitogenic stimulation

Abstract

The Na+/H+ exchanger 1 NHE-1 is a ubiquitous membrane transporter mainly involved in pH and cell volume regulation. NHE-1 activation by H+ is carried out according to the Monod-Wyman-Changeux model in which the dimeric NHE-1 oscillates between a low and a high affinity conformation, the balance of which being defined by the ratio between the two forms L0. Influence of cholesterol- and caveolin-rich microdomains on NHE-1 activity is examined, by using a cholesterol depleting agent, methyl-β-cyclodextrin (MBCD). MBCD induce NHE-1 activation, by modulating its allosteric balance, these effects being reverted by cholesterol repletion. This activation appears to be associated with NHE-1 relocalization outside caveolin-rich microdomains and distinct from mitogenic stimulation of NHE-1, since MBCD and serum cotreatments are additive; besides, serum alone stimulates this transporter without modifying its localization. Finally, MBCD activate a serum-insensitive mutated NHE-1 form and this process occurs independently of MAP kinase phosphorylation. In conclusion, the membrane localization of NHE-1 in or out microdomains seems to be an essentiel regulator of NHE1 activity, independently of mitogenic action.