Temporal Relationships between Isometric Force, Phosphorylase, and Protein Kinase Activities in Vascular Smooth Muscle

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Abstract
Vascular smooth muscle contractility is tightly coupled to ATP production by intermediary metabolism. To elucidate mechanisms underlying coordination of metabolism and contractility the time course of isometric force, and the activation of phosphorylase and cAMP-dependent protein kinases was studied during stimulation of bovine coronary arterial strips with KCl. Isometric force reached a maximum after 10 min of exposure to 30 mM KCl (ED90) [dose causing 90% effectiveness] and was sustained throughout the subsequent 20-min period of contraction. Activation of phosphorylase was biphasic: enzymic activity reached a maximum (176 .+-. 10% of control) after 3 min of contraction and then, though remaining above control, activity declined to a lower level (135 .+-. 7% of control). No change occurred in the activity ratios for cAMP-dependent protein kinase assessed in either the presence (type II isozyme) or absence (type I isozyme) of 0.5 M NaCl. The activation of phosphorylase during K+-induced contraction is independent of the cAMP system. The biphasic activation of phosphorylase may reflect transient changes in the intracellular concentration of Ca2+ or the activation of a phosphatase(s) during the response.