Abstract
Effects of cyclic adenosine 3':5'-monophosphate (cyclic AMP)-dependent protein kinase were studied in sarcoplasmic reticulum prepared from cardiac and slow and fast (white) skeletal muscle. Cyclic AMP-dependent protein kinase failed to catalyze phosphorylation of fast skeletal muscle microsomes as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cyclic AMP-dependent protein kinase was without effect on calcium uptake by these microsomes. Treatment of cardiac microsomes obtained from dog, cat, rabbit, and guinea pig with cyclic AMP-dependent protein kinase and ATP resulted in phosphorylation of a 22,000-dalton protein component in the amounts of 0.75, 0.25, 0.30, and 0.14 nmol of phosphorus/mg of microsomal protein, respectively. Calcium uptake by cardiac microsomes was stimulated 1.8- to 2.5-fold when microsomes were treated with cyclic AMP-dependent protein kinase. Protein kinases partially purified from bovine heart and rabbit skeletal muscle were both effective in mediating these effects on phosphorylation and calcium transport in dog cardiac sarcoplasmic reticulum. Slow skeletal muscle sarcoplasmic reticulum also contains a protein with a molecular weight of approximately 22,000 that can be phosphorylated by protein kinase. Phosphorylation of this component ranged from 0.005 to 0.016 nmol of phosphorous/mg of microsomal protein in dog biceps femoris. A statistically significant increase in calcium uptake by these membranes was produced by the protein kinase. Increases in protein kinase-catalyzed phosphorylation of a low molecular weight microsomal component and in calcium transport by sarcoplasmic reticulum of cardiac and slow skeletal muscle may be related to the relaxation-promoting effects of epinephrine seen in these types of muscle. Conversely, the absence of a relaxation-promoting effect of epinephrine in fast skeletal muscle may be associated with the lack of effect of cyclic AMP and protein kinase on calcium transport by the sarcoplasmic reticulum of this type of muscle.
Highlights
From the Division of Cardiology, Department of Medicine, and the Department of Physiology and Biophysics, The Mount Sinai School of Medicine of the City University of New York, New York, New York, 10029
We present evidence that suggests that, unlike its effect in fast skeletal muscle, a relaxation-promoting effect of epinephrine in cardiac and slow skeletal muscle may be related to the ability of protein kinase to phosphorylate a 22,000-dalton component and stimulate calcium transport in sarcoplasmic reticulum obtained from these types of muscle
At 10 min, aliquots of the Muscle Microsomes-Treatment of sarcoplasmic reticulum prepared from fast skeletal muscle of rabbit with cyclic AMP and protein kinase had no effect on the initial rate of calcium uptake when measured by Procedure A (Table I)
Summary
Effects of cyclic adenosine 3’:5’-monophosphate (cyclic AMP)-dependent protein kinase were studied in sarcoplasmic reticulum prepared from cardiac and slow and fast (white) skeletal muscle. AMP-dependent protein kinase failed to catalyze phosphorylation of fast skeletal muscle microsomes as determined by sodium dodecyl sulfate-polyacrylamide protein kinase was without effect on calcium uptake gel electrophoresis. Treatment of cardiac microsomes obtained from dog, cat, rabbit, and guinea pig with cyclic AMP-dependent protein kinase and ATP resulted in phosphorylation of a 22,000.dalton protein component in the amounts of 0.75, 0.25, 0.30, and 0.14 nmol of phosphorus/mg of microsomal protein, respectively. 1.8- to 2.5-fold when microsomes were treated with cyclic AMP-dependent protein kinase. Protein kinases partially purified from bovine heart and rabbit skeletal muscle were both effective in mediating these effects on phosphorylation and calcium transport in dog cardiac sarcoplasmic reticulum
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