Lipid-protein interactions in sarcoplasmic reticulum are not perturbed by ionophore A23187. An EPR and fluorescence study.

The divalent-cation ionophore A23187 at micromolar concentrations prevents the ATP-dependent accumulation of calcium into sarcoplasmic reticulum vesicles. Under the same conditions and throughout the temperature range of 4 degrees-37 degrees C, A23187 has no effect on either the rotational motion of the Ca2+ -ATPase in the membrane, or on the mobility of the lipid acyl chains. The steady-state fluorescence polarization of a polyene fluorescent probe incorporated into the membrane lipids was similarly unaffected by the ionophore. These results show conclusively that the mechanism of action of the ionophore does not involve significant of lipid-protein interactions.