TEMPERATURE-DEPENDENCY OF THE FUNCTIONAL ACTIVITIES OF DOG CARDIAC SARCOPLASMIC-RETICULUM - COMPARISON WITH SARCOPLASMIC-RETICULUM FROM RABBIT AND LOBSTER MUSCLE

Temperature-dependency studies of the functional activities of sarcoplasmic reticulum vesicles from different muscle sources have been carried out. The energies of activation of transport and hydrolytic processes of microsomes from dog heart have been found to be higher than those obtained with rabbit and lobster skeletal muscle. This difference is reduced in the presence of membrane perturbing agents as the detergent Triton X-100 or the Ca2+-ionophore A-23187, indicating that the different level of the functional ability of microsomal vesicles isolated from different tissues might be due mainly to differences in the lipid environment. Thermodynamic parameters (ΔG‡, ΔH‡, ΔS‡ of the Ca2+-transport and Ca2+-dependent ATPase reactions of cardiac microsomes pre-phosphorylated with cAMP-dependent protein kinase have been determined. The stimulatory effect of protein kinase can be interpreted as a change in the fluidity of the hydrophobic microenvironment of the ATPase molecules. The transport process if entropically more favourable in pre-phosphorylated than in control microsomes. © 1979.