EFFECT OF HORMONAL AND NEURONAL AGENTS ON ADENYLATE-CYCLASE FROM SMOOTH-MUSCLE OF THE GASTRIC ANTRUM

Smooth muscle adenylate cyclase of a membrane preparation of canine gastric antrum has been characterized, and the effect of hormonal and neuronal agents examined. The enzyme is active in the presence of Mg2+ or Mn2+, but is inhibited by Ca2+. The Km is 0.5 mM ATP, similar to the Km of skeletal muscle adenylate cyclase. The enzyme is activated by isoproterenol but not norepinephrine, consistent with a β2-catecholamine receptor-adenylate cyclase interaction. Secretin activates the enzyme in concentrations as low as 1 · 10-11 M, while glucagon was effective only at 1 · 10-6 M. Prostaglandin E1 and E2 have a biphasic effect with activation of adenylate cyclase at 1 · 10-5 M and a small but significant inhibition of enzyme activity at 1 · 10-11 M. © 1979.