title: Effects of bethanechol and the octapeptide of cholecystokinin on colonic smooth muscle in the cat.
abstract: The aim of this study is to compare the action of the cholinergic agonist, bethanechol, with the action of the octapeptide of cholecystokinin (CCK-OP) on feline circular colonic smooth muscle membrane potential and isometric tension, using the double sucrose gap. Depolarization of the membrane greater than 10 mV by K+ or bethanechol increased tension and spontaneous spike activity. CCK-OP (10(-9) M) depolarized the membrane (6.1 +/- 1.3 mV) without an increase in tension or spike activity. Depolarization of the membrane by increasing [K+]o was associated with a decrease in the membrane resistance. The slow-wave duration (2.3 +/- 0.2 s) was unchanged by administration of K+ or bethanechol but was prolonged after increasing concentrations of CCK-OP. The maximum effect occurred at a 10(-10) M concentration of CCK-OP (4.5 +/- 0.4 s, P less than 0.01). At higher concentrations of CCK-OP (greater than 10(-10) M), the slow-wave pattern became disorganized. Addition of increasing concentrations of [K+]o or bethanechol, but not CCK-OP, stimulated a concentration-dependent increase in the maximum rate of rise (dV/dtmax) of an evoked spike potential. These studies suggest 1) bethanechol decreased the membrane potential without altering the slow-wave activity, whereas CCK-OP has a minimal effect on the membrane potential but distorted the slow-wave shape; 2) an increased amplitude of the spike and dV/dtmax of the spike were associated with an increase in phasic contractions after bethanechol or increased [K+]o; 3) the lack of an increase in the spike amplitude and the dV/dtmax to CCK-OP was associated with no increase in phasic contraction.
mesh_terms: D000818:Animals; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology*; D002415:Cats; D003106:Colon / Q000187:drug effects* / Q000502:physiology; D004594:Electrophysiology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D012844:Sincalide / Q000494:pharmacology*
chemical_list: D001626:Bethanechol Compounds; D018723:Bethanechol; D012844:Sincalide; D011188:Potassium