title: Effect of pH value on the drug-initiated contractility of small intestine "in vitro".
abstract: The influence of different pH values in nutrient media on the drug-initiated contractility of rectal smooth muscle was isometrically investigated. The following results were obtained: (1) The response to drugs is potentiated in alkali media and is reduced in acidic media. (2) Facilitated responses in alkali media were lost with the removal of CaCl2 and the reduction of responses was markedly enhanced with the increase in H+ or in the absence of CaCl2. (3) Analysis with an atomic absorption spectrophotometer, shows that H+ may compete with Ca2+ in transmembrane transport. (4) Removal of NaCl can elicit the release of Ca2+ and this action was diminished in acidic conditions. (5) The contractile system of muscle cells was also inhibited by lowering pH values in nutrient media. Thus, interference with mobilization of Ca2+ by H+ is considered to be responsible for modifying the contractions of rectal smooth muscle in mice.
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000187:drug effects; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D012964:Sodium / Q000502:physiology
chemical_list: D001464:Barium; D012964:Sodium; D002118:Calcium