title: The influence of harmaline on the movements of sodium ions in smooth muscle of the guinea pig ileum.
abstract: The effect of changing the extracellular concentration of both Na+ and K+ on the longitudinal muscle of the guinea-pig ileum was studied in the presence and absence of harmaline. A decrease in extracellular Na+ concentration was found to produce a dose-dependent contractile response, which may suggest the existence of a Na-Ca exchange mechanism in this muscle. Harmaline (2 X 10(-4) M) was found to reversibly inhibit this contraction and was also found to selectively block the tonic component of high-K induced contradictions. In view of the fact that harmaline is a non-competitive inhibitor of Ca-induced contractions (Hider et al., Europ. J. Pharmacol., 71, 87, 1981), the action of harmaline was interpreted as being a specific inhibitor of the Na-Ca exchange mechanism, binding specifically to Na+ coordination sites.
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006246:Harmaline / Q000494:pharmacology*; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D012964:Sodium; D006246:Harmaline; D011188:Potassium; D002118:Calcium