title: The role of intracellular calcium stores in motilin induced contractions of the longitudinal muscle of the rabbit duodenum.
abstract: The contraction of longitudinal muscle strips of the rabbit duodenum in response to motilin and acetylcholine was investigated in normal and high K+-solutions in the presence and absence of external calcium, in order to demonstrate the existence of pharmaco-mechanical coupling for motilin and to examine whether the peptide mobilizes calcium from an intracellular store. In depolarized smooth muscle (140 mM K+), motilin (3.2 x 10(-9)-1 x 10(-7) M) and acetylcholine (1 x 10(-5) M) were still capable of causing a considerable, transient, concentration-dependent contraction in the presence of Ca2+. The 'extra'-contraction to motilin was not blocked by tetrodotoxin (1 microgram/ml) nor by atropine (10(-7) M), but acetylcholine (10(-5) M) was blocked by atropine. Verapamil (10(-7) M) could selectively block the K+ contraction without affecting the extra agonist contraction. Nitroprusside was ineffective up to 10(-4) M in high K+-solutions, but in normal Hepes-buffer it caused a concentration-dependent rightward shift of the concentration-response curve of motilin and acetylcholine contractions. In a calcium-depleted medium, high K+-depolarized muscle strips were still responsive to motilin and acetylcholine, but higher concentrations (10(-6) M) were needed than in the presence of calcium and the contractions reached only 57 +/- 11% and 74 +/- 9% respectively of the maximal contraction in 1.2 mM Ca2+ containing solutions. The response to motilin (10(-6) M) was not only smaller than that to acetylcholine (10(-5) M), it also faded more rapidly with time.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Gastroenterological Research, University of Leuven, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Matthijs
authors.forename: T L
authors.initials: TL
authors.lastname: Peeters
authors.forename: G
authors.initials: G
authors.lastname: Vantrappen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D004386:Duodenum / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009037:Motilin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009599:Nitroprusside / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D009599:Nitroprusside; D013779:Tetrodotoxin; D009037:Motilin; D001285:Atropine; D014700:Verapamil; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium