Phosphodiesterase protein activator stimulates calcium transport in cardiac microsomal preparations enriched in sarcoplasmic reticulum

Protein activator of cyclic nucleotide phosphodiesterase from bovine brain (9 μg/0.5 ml) was found to stimulate ATP-dependent Ca 2+ - transport in dog cardiac microsomal preparations enriched in sarcoplasmic reticulum. Both oxalate-dependent calcium uptake and ATP-dependent calcium binding were increased. Cyclic AMP-dependent protein kinase (Sigma, type 1, 25 μg/0.5 ml) and cyclic AMP (1 μM) also stimulated calcium uptake and the presence of a maximal stimulatory concentration of the phosphodiesterase activator produced an additive elevation of calcium uptake indicating separate mechanisms of action and potentially different modulatory roles for these two systems in the control of calcium transport.