Measurement of sarcoplasmic reticulum Ca2+ ATPase activity using high-performance liquid chromatography

The goal of this investigation was to develop an assay whereby we could measure changes in ATP, ADP, and phosphocreatine (PCr) during stimulation of the sarcoplasmic reticulum (SR) Ca2+ ATPase. After stopping the enzyme reaction, compounds were extracted by perchloric acid and separated by reversed-phase high-performance liquid chromatography (HPLC). Absorbance of ATP and ADP was monitored at 260 nm, and detection of PCr was done at 205 nm. Chromatograms show that peaks associated with each compound are clearly separated and easily detected. The SR Ca2+ ATPase assay was run for various time periods and using varying free [Ca2+]. The changes in ATP and ADP contents were linear with increasing time and varied as expected with increasing free [Ca2+]. The ATPase activities determined using changes in ATP and ADP were nearly identical to those determined using previously established assays. When PCr was added to the assay, we were able to confirm that the Ca2+ ATPase uses ATP that is synthesized locally from PCr via creatine kinase (CK). The results indicate that this is a valid and reliable method for examining SR Ca2+ ATPase activity and for investigating its interaction with CK.