title: Relations between Na+, Ca2+ and K+ extracellular concentrations and the effects of PGE2 on the longitudinal muscle of the guinea pig caecum.
abstract: Prostaglandin E2 (PGE2) stimulated the electrical and contractile activities of the isolated longitudinal muscle of the guinea pig caecum. Pretreatment of the smooth muscle strips with Na+-deficient solutions decreased the stimulant effects of PGE2. The action of PGE2 was abolished on the background of high K+ and low Na+ solutions. A reduction of extracellular Ca2+ to 0.2 mM did not change significantly the responses to PGE2. The addition of D-600 depressed both spike potential activity and contractions and only a weak depolarization occurred after PGE2. However, the effects of PGE2 were not completely inhibited after removing Ca2+ from the solution. These observations show that the stimulant effects of PGE2 on the longitudinal muscle of the guinea pig caecum depend mainly on the extracellular concentration of Na+ and are less sensitive to the lack of Ca2+. It is suggested that under certain conditions Na+ may transfer currents through the calcium ion channels in the smooth muscle membrane.
authors.forename: K
authors.initials: K
authors.lastname: Venkova
authors.forename: R
authors.initials: R
authors.lastname: Radomirov
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002432:Cecum / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D015232:Dinoprostone; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011188:Potassium / Q000378:metabolism*; D011458:Prostaglandins E / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
chemical_list: D011458:Prostaglandins E; D012964:Sodium; D015232:Dinoprostone; D011188:Potassium; D002118:Calcium