A possibility of substituting Ca2+ by Ba2+ or Mn2+ during the contractile processes of complex stomach smooth muscles.
In vitro experiments were carried out on muscle strips from different compartments of sheep complex stomach. The following conclusions were drawn: 1. In Ca2+-free medium containing EDTA (0.5 mM) proximal and antral abomasum preparations are mechanically inactive. The addition of BaCl2 (0.2-1 mM) induces phasic contractions in the rumen and antrum strips. In contrast to the simple stomach Ba2+ causes a significant increase in the tone of the rumen and proximal abomasum preparations. This tonic contraction is verapamil resistant and is completely suppressed by sodium nitroprusside. 2. The Ba2+ effect is not mediated by cholinergic or adrenergic systems. Ba2+ can substitute Ca2+ in generating both phasic and tonic contractions in complex stomach smooth muscles. 3. Compared with the simple stomach Mn2+ (0.2-0.8 mM) influences neither the ACh-induced activity in normal nutrient medium nor the tone of the rumen and proximal abomasum preparations in Ca2+-free solution.
D000018:Abomasum / Q000187:drug effects; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D012756:Sheep; D013270:Stomach / Q000187:drug effects
D001464:Barium; D005711:Gallopamil; D008345:Manganese; D001285:Atropine; D002118:Calcium