Do membrane lipids modify the ouabain-sensitivity of cardiac (Na,K)ATPase?

We investigated whether membrane lipids can alter the affinity of cardiac (Na,K)ATPase (ATP phosphohydrolase, EC 3.6.1.6) for ouabain. We recombined partially (80-95%) delipidated membrane proteins from a digitalis-sensitive species (dog) with membrane lipids from a relatively digitalis-insensitive species (rat) or vice versa, and estimated the affinity of (Na,K)ATPase for ouabain in these hybrid membranes by measuring the half-maximal inhibitory concentration (I50). Delipidation reduced the enzyme activity by 90-95%, but 40-60% of the original activity could be restored with lipids from the same or from the other species and distribution of [14C]phosphatidylcholine showed complete mixing between the native and foreign lipids. In these hybrid cardiac membranes affinity (I50) for ouabain was determined by the origin of the (Na,K)ATPase protein and was not modified by the change in membrane lipids.