Mechanisms of Na-Ca Exchange Inhibition by Amphiphiles in Cardiac Myocytes: Importance of Transbilayer Movement

The membrane lipid environment and lipid signaling pathways are potentially involved in the modulation of the activity of the cardiac Na-Ca exchanger (NCX). In the present study biophysical mechanisms of interactions of amphiphiles with the NCX and the functional consequences were examined. For this purpose, intracellular Ca concentration jumps were generated by laser-flash photolysis of caged Ca in guinea-pig ventricular myocytes and Na-Ca exchange currents (INa/Ca) were recorded in the whole-cell configuration of the patchclamp technique. The inhibitory effect of amphiphiles increased with the length of the aliphatic chain between C7 and C10 and was more potent with cationic or anionic head groups than with uncharged head groups. Long-chain cationic amines (C12) exhibited a cut-off in their efficacy in INa/Ca inhibition. Analysis of the time-course, comparison with the Ni-induced INa/Ca block and confocal laser scanning microscopy experiments with fluorescent lipid analogs (C6and C12-NBD-labeled analogs) suggested that amphiphiles need to be incorporated into the membrane. Furthermore, NCX block appears to require transbilayer movement of the amphiphile to the inner leaflet (‘‘flip’’). We conclude that both, hydrophobic and electrostatic interactions between the lipids and the NCX may be important factors for the modulation by lipids and could be relevant in cardiac diseases where the lipid metabolism is altered.