INFLUENCE OF EXTRACELLULAR CALCIUM ON MUSCARINIC RECEPTORS IN VASCULAR SMOOTH-MUSCLE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 223  (2) , 223-230
Abstract
The influence of extracellular calcium (Ca2+) on the affinity of cholinergic agonists and antagonists for muscarinic receptors was studied in isolated rabbit aortic strips. Dose-response curves which demonstrate the effect of acetylcholine on the force of contraction in the presence of various Ca2+ concentrations were made. The affinity constant was calculated and the intrinsic activity was determined at each of the different Ca2+ concentrations used. The relationship between extracellular Ca2+ and the pA2 value for atropine was determined. No apparent relationship between the affinity of acetylcholine for the cholinergic receptors and Ca2+ concentration in vascular muscle was demonstrated. The intrinsic activity was altered when extracellular Ca2+ was varied. Atropine was effective to the same degree in the presence and complete absence of Ca2+. These results are discussed in relation to the dependency of acetylcholine on extracellular Ca2+ to induce contractile responses after receptor occupancy in vascular muscle.