Activation of Phosphorylase by Anoxia and Dinitrophenol in Rabbit Colon Smooth Muscle: Relation to Release of Calcium from Mitochondria

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Abstract
The effect of anoxia or 2,4-dinitrophenol (DNP) on the phosphorylase a activity and the Ca content in subcellular fractions from rabbit colon smooth muscle was studied. Anoxia for 15 min and DNP (6.6 .times. 10-5 M) for 5 min increased phosphorylase a activity. The Ca content in the mitochondrial subfraction, prepared from the anoxic- or DNP-treated intact muscle and determined by atomic absorption spectroscopy, was reduced. The Ca content in the nuclear and the microsomal fractions was not changed in preparations with a normal Ca content. When the muscle was incubated for 60 min in a Ca2+-free medium containing 2.0 mM EGTA, the Ca content in the mitochondrial fraction was reduced to 38% of the control. This Ca level was further reduced and the phosphorylase a activity was increased by DNP in this Ca-poor muscle. In these preparations the Ca content of the microsomal + supernatant fraction increased. Only when the muscle was incubated initially in an anoxic medium containing 0.1 mM Ca2+ for 120 min and subsequently in an oxygenated medium containing 0.1 mM Ca2+ for 20 min, did DNP fail to activate phosphorylase and decrease the Ca content in the mitochondrial fraction. Mitochondrial Ca2+ release was a regulatory factor of anoxic-induced glycogenolysis.