Dissociation of phosphorylase a activation and contractile activity in rat portal vein.
Isometric force, glycogen phosphorylase activity and lactate production were measured under conditions known to alter intracellular Ca2+ and cAMP to assess the role of these messengers in the coordination of metabolism with contractility in rat portal vein. Total phosphorylase (a + b) activity, was independent of treatment. The activity ratio phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on or high-K+ medium, and 0.57 after 20 min treatment with 10(-5) M isoproterenol + 10(-4) M papaverine. Under both of these conditions the muscle was totally relaxed. The phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on extracellular Ca2+, both in normal and depolarizing medium. This suggests a lower Ca2+ sensitivity of the contractile than the phosphorylase system under these conditions, known to be associated with raised intracellular cAMP. During spontaneous activity and high-K+ induced contractures phosphorylase activity was increased compared to the relaxed state in Ca2+-free medium. A high level of phosphorylase activity (0.48) was elicited by the addition of 300 mM sucrose, which induces a contracture in Ca2+-free medium. Lactate production was in general parallel to phosphorylase activity, except for a relative increase in anoxia. The results suggest that in the intact cell the Ca2+-mediated linkage of contraction and phosphorylase may be modified by cAMP changing the Ca2+ sensitivities of the two systems in opposite directions.
D000818:Animals; D002118:Calcium / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006019:Glycolysis / Q000187:drug effects; D007537:Isometric Contraction / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D007773:Lactates / Q000096:biosynthesis; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000201:enzymology* / Q000502:physiology; D010208:Papaverine / Q000494:pharmacology; D010762:Phosphorylase a / Q000378:metabolism*; D010763:Phosphorylase b / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism*; D011169:Portal Vein / Q000201:enzymology; D051381:Rats
D007773:Lactates; D010208:Papaverine; D000242:Cyclic AMP; D010762:Phosphorylase a; D010763:Phosphorylase b; D006005:Phosphorylases; D007545:Isoproterenol; D002118:Calcium