title: Sources of calcium for contraction of distal circular muscle or taenia coli in the rabbit.
abstract: Studies were performed on proximal taenia coli and distal circular muscle from the rabbit to determine if the source of Ca2+ required for bethanechol stimulation of contraction was similar after permeabilizing the tissues with saponin. The EC50 for Ca2+ stimulation of contraction was pCa 6.1 +/- 0.1 for both tissues. The peak response occurred at pCa 4.5. The addition of 1 microM calmodulin did not alter the Ca2+ EC50 or the peak response. Caffeine (20 mM) stimulated contraction of both taenia coli and distal circular muscle. The caffeine-stimulated contractile response was threefold greater in the taenia than in the distal circular muscle (P less than 0.05). Perfusion of thin strips of colonic muscle with buffer, containing 10(-7) M Ca2+, reduced the amplitude of bethanechol-stimulated contraction. The perfusion time to reduce the contraction by 50% was greater in the proximal muscle (2.4 +/- 0.1 min) than in the distal muscle (1.1 +/- 0.5 min) (P less than 0.001). These data suggest that 1) the intracellular Ca2+ concentration necessary for contraction is similar in the proximal and distal colon and 2) the intracellular Ca2+ stores appear to be greater in proximal taenia coli compared with distal circular muscle.
mesh_terms: D000818:Animals; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000502:physiology; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012984:Software
chemical_list: D001626:Bethanechol Compounds; D002147:Calmodulin; D018723:Bethanechol; D002110:Caffeine; D011188:Potassium; D002118:Calcium