Eicosonoid metabolism and beta-adrenergic mechanisms in coronary arterial smooth muscle: potential compartmentation of cAMP.

Beta-Adrenergic relaxation in bovine coronary arteries is enhanced by inhibition of eicosonoid metabolism and inhibited by its stimulation. We investigated the interaction between eicosonoid metabolism and beta-adrenergic mechanisms by studying the effect of perturbations of eicosonoid metabolism on vascular adenosine 3',5'-monophosphate (cAMP) content and the cAMP-dependent relaxation of isometric force and activation of glycogen phosphorylase. KCl (35 mM) elicited a contraction, activated phosphorylase, and slightly decreased cAMP content. Isoproterenol (10(-7) M) relaxed the KCl contraction, further increased phosphorylase activity, and increased cAMP. Neither indomethacin (5 X 10(-6) M) nor arachidonic acid (3 X 10(-5) M) affected the KCl contraction, but arachidonic acid increased both cAMP and phosphorylase activity and indomethacin decreased cAMP. Indomethacin potentiated the relaxation induced by isoproterenol but inhibited the activation of phosphorylase and had no effect on the isoproterenol-induced increase in cAMP. Arachidonic acid, on the other hand, inhibited the isoproterenol-induced relaxation but potentiated both the increases of phosphorylase activity and cAMP. Thus neither relaxation nor phosphorylase activity was related in a straightforward manner to the total cAMP content. A direct relation between cAMP, relaxation, and phosphorylase can be reconciled with the antiparallel effects of alterations of eicosonoid metabolism observed in this study by a proposed model in which the effects of cAMP are assumed to be functionally compartmentalized.

Temporal relationships between isometric force, phosphorylase, and protein kinase activities in vascular smooth muscle.

Vascular smooth muscle contractility is tightly coupled to ATP production by intermediary metabolism. To elucidate mechanisms underlying coordination of metabolism and contractility we studied the time course of isometric force, and the activation of phosphorylase and cAMP-dependent protein kinases during stimulation of bovine coronary arterial strips with KCl. Isometric force reached a maximum after 10 min of exposure to 30 mM KCl (ED90) and was sustained throughout the subsequent 20-min period of contraction. In contrast, 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). However, 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. These data suggest that 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.

Concentration and time-dependent relationships between isosorbide dinitrate-induced relaxation and formation of cyclic GMP in coronary arterial smooth muscle.

This study is based on the hypothesis that isosorbide dinitrate (ISDN)-induced relaxation of coronary arterial smooth muscle is causally linked to formation of cyclic (c) GMP. The hypothesis requires the extent of relaxation to be correlated to both time-and concentration-dependent increases in coronary content of cGMP. Accordingly, studies were performed with bovine coronary arterial strips to determine the relationships among isometric force and coronary content of cGMP and cAMP with respect to time of exposure to and concentration of ISDN. Cyclic nucleotide levels were determined by radioimmunoassay. No change in cAMP levels was observed during ISDN-induced relaxation of KCl contracted strips. In sharp contrast, cGMP levels increased significantly with time of exposure and concentration of ISDN stimulation. Moreover, the addition of methylene blue, a reported inhibitor of guanylate cyclase, to the bathing medium significantly inhibited the relaxation and cGMP increase during ISDN stimulation. In addition, prolonged exposure to ISDN resulted in a redevelopment of force with a parallel decrease in cGMP content. The increase in cGMP during ISDN stimulation also occurs in the absence of depolarization by KCl and in an essentially Ca++-free medium. These data support the hypothesis that the relaxation of coronary arterial strips in response to ISDN stimulation is causally linked to cGMP.

Motor-end-plate and nerve distribution in a histochemically compartmentalized pennate muscle in the cat.

Previous investigations in this laboratory have shown the flexor carpi radialis muscle (FCR) of the cat to be compartmentalized with regard to the distribution of muscle fiber types. This study was undertaken to determine whether each compartment of the FCR had a distinct motor innervation band, or whether there was only one innervation band, as has been reported previously for other muscles. In order to assess variation in motor innervation banding patterns, the innervation bands were correlated with the muscle-tendon architecture. Each compartment of the FCR possessed a distinct innervation band. In addition, it was observed that the nerve to the FCR divided into a number of separate intramuscular branches which were distributed to the different histological compartments. It is possible that muscle fibers innervated by a single intramuscular nerve branch, and possessing a discrete innervation band, are locally organized within subdivisions of the FCR. It is hypothesized that the compartmental organization of the FCR would allow discrete regions of the muscle to function independently when performing different motor tasks.