title: An analysis of the action of cations of the lanthanide series on the mechanical responses of guinea-pig ileal longitudinal muscle.
abstract: 1. The inhibitory effects of lanthanide cations (Ln3+) on mechanical responses and 45Ca uptake in guinea-pig ileal longitudinal smooth muscle were studied. 2. Ln3+ strongly inhibited the phasic and tonic component of the response to the muscarinic agonist cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD) the two components being affected to the same extent. Inhibition was also obtained for the responses evoked by high K+ but here the effect was mainly on the phasic response, the tonic component was merely delayed. 3. Other members of the Ln3+ series, with the exception of cerium, were found to be more effective than lanthanum in their ability to inhibit the CD response. Thulium, Tm3+, the thirteenth member of the series was the most effective cation. 4. Analysis of 170Tm uptake revealed at least two components. The concentration-dependence of one component, saturating at 2-5 x 10(-6) Tm, corresponded closely to that of the inhibitory effect of Tm3+ on contraction. 5. 170Tm uptake as a function of time showed a secondary rise after 30 min of exposure to the lanthanide. 6. Although 2-5 x 10(-6) M-Tm3+ produced 90% inhibition of the CD and the high K+ induced responses significant reduction of 45Ca uptake by the muscle was only detected when much higher Tm3+ concentrations (greater than or equal 10(-3) M-Tm3+) were used. 7. It is concluded that Ln3+ combine with membrane sites specifically involved in Ca2+ translocation during excitation-contraction coupling.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002563:Cerium / Q000494:pharmacology; D004148:Dioxolanes / Q000037:antagonists & inhibitors; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D008674:Metals, Rare Earth / Q000494:pharmacology*; D008744:Methylamines / Q000037:antagonists & inhibitors; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D013932:Thulium / Q000378:metabolism / Q000494:pharmacology
chemical_list: D004148:Dioxolanes; D008674:Metals, Rare Earth; D008744:Methylamines; D002563:Cerium; D007811:Lanthanum; D013932:Thulium; D011188:Potassium; D002118:Calcium