title: Calcium-based evaluation of dose-response curves of papaverine-like relaxants in guinea-pig taenia coli.
abstract: Using CaCl2 dose-contraction curves in 165.6 mM K(+)- depolarized guinea-pig taenia coli, the maximal contraction level induced by 30 mM CaCl2, and the maximal relaxation level induced by Ca-free solution were treated and 0% and 100% relaxation, respectively. Then four kinds of contraction level were compared: (1) the normal level, (2) 5.5 microns acetylcholine (ACh)-induced contraction, and (3) 1.65 mM ACh- or 3 mM BaCl2-induced contraction in normal solution; and (4) 2.2 and 30 mM CaCl2-induced contraction in K(+) depolarizing solution. The relaxing effects of papaverine, MnCl2, and isoproterenol at these different contraction levels were compared. Papaverine- and MnCl2-induced relaxation of the higher contraction levels [a part of (2), (3) and (4)] seem to reflect a mechanism of the intracellular calcium mobilization, being quite different from relaxation induced by papaverine-like relaxants and isoproterenol at the lower contraction levels [(1) and part of (2)]. The latter phenomenon seems to reflect mechanisms related to cyclic AMP. Papaverine inhibited competitively BaCl2-induced contraction only in K(+) depolarized tissues, suggesting a mechanism of direct reaction with the intracellular Ca store.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds; D002118:Calcium / Q000494:pharmacology*; D002712:Chlorides; D003106:Colon / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D010208:Papaverine / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D017609:Barium Compounds; D002712:Chlorides; D010276:Parasympatholytics; C024986:barium chloride; D001464:Barium; D013806:Theophylline; D010208:Papaverine; D007545:Isoproterenol; D000109:Acetylcholine; D002118:Calcium