Sarcoplasmic reticulum (SR) native vesicles incorporating Ca-ATPase are adsorbed on a solid-supported lipid membrane (SSM). Upon adsorption, the ion pumps are chemically activated by concentration jumps of ATP and the capacitive current transients generated by SR Ca-ATPase are measured under potentiostatic conditions. The Michaelis-Menten constant, KM, for ATP is evaluated by varying the concentration of ATP in the activating solution. This preliminary result shows that ion transport by SR Ca-ATPase can be suitably investigated by a technique based on concentration jumps on an SSM.