Effects of detergents on P-glycoprotein atpase activity: differences in perturbations of basal and verapamil-dependent activities.

P-glycoprotein (P-gp), a plasma membrane glycoprotein associated with the multidrug resistance phenotype, is responsible for the ATP-dependent efflux of various amphiphilic drugs. Using membrane vesicles prepared from the multidrug resistant cell line DC-3F/ADX, we studied the perturbation of the basal (i.e. in the absence of drug) and verapamil-dependent P-gp ATPase activities induced by various detergents, at non-solubilizing, as well as at solubilizing, concentrations. The progressive membrane solubilization with increasing detergent concentration was monitored by light scattering and centrifugation experiments. For non-solubilizing detergent concentrations, all tested detergents except DOC induced a partial inhibition of P-gp ATPase activity, which was not correlated with the amount of the various tested detergents incorporated in the membranes. Analysis of the verapamil-induced P-gp activation reveals that P-gp ATPase activity is differently modulated by the various detergents at non-solubilizing concentrations. Thus, specific interactions between P-gp and detergents are more likely to occur rather than a global membrane perturbation. After solubilization by the various tested detergents, the basal P-gp ATPase activity was virtually completely inhibited, except in the presence of CHAPS which was able to preserve this activity at a level comparable to that measured in native membranes. However, the verapamil-induced P-gp ATPase activation was lost during P-gp solubilization by CHAPS, but recovered after dilution of CHAPS below its critical micellar concentration. These observations indicate specific interactions between P-gp and CHAPS molecules within the mixed micelles. On the whole, our data evidencing specific interactions P-gp/detergents are consistent with the location of the drug transport sites on P-gp transmembrane domains.