Action of caffeine upon calcium accumulation by sarcoplasmic reticulum preparations isolated from rabbit heart [Abstract]

Caffeine partly influences mechanical performance of heart muscle by affecting internal membrane function. In skeletal and heart muscle caffeine alters calcium ac- cumulation by isolated sarcoplasmic reticulum fractions but the manner of its action is uncertain. Sarcoplasmic reticulum fractions were isolated from rabbit heart by differential centrifugation. Calcium accumulation, with and without oxalate, was followed using dual-wavelength spectrophotometry with murexide at 35°C. The calcium accumulation data were analysed according to first order kinetics. ATPase activity (basic and calcium activated) was also measured. Calcium accumulation both with and without oxalate was inhibited in a dose related manner by caffeine. At low but not high concentrations calcium activated ATPase activity was increased by caffeine but in the presence of oxalate it was not altered by caffeine at any calcium concentration. Caffeine did not alter the basic ATPase activity. The findings support the con- clusion that caffeine reduced calcium accumulation by altering the passive permeability of the sarcoplasmic recticulum vesicles to calcium