title: Availability of calcium for noradrenergic contraction of the mouse isolated vas deferens is not altered during tolerance to and dependence on morphine.
abstract: 1. The present study assesses the influence of tolerance to and dependence on morphine on the availability of Ca2+ for contraction of the mouse isolated vas deferens induced by noradrenaline (NA). 2. Reducing Ca2+ content in the bathing solution from 2.5 to 1.2 or 0.6 mM significantly reduced the magnitude of NA-induced contractions. This effect was similar in preparations obtained from control and tolerant/dependent mice (P greater than 0.05 at any Ca2+ concentration). 3. Omission of Ca2+ from the bathing solution caused a rapid and similar loss of responsiveness to a maximally effective concentration of NA (300 microM) in both groups (t1/2 less than 3 min, P greater than 0.05). 4. Vasa deferentia obtained from control and tolerant/dependent mice were equally susceptible to non-competitive antagonism of NA-induced contraction by verapamil (3 to 30 microM; pD2' values of 5.50 and 5.26, respectively, (P greater than 0.05 at any concentration of verapamil). 5. Preparations from tolerant/dependent mice displayed significant supersensitivity to NA, the magnitude of which was not influenced by modifying the Ca2+ concentration in the bathing medium (2.6- and 1.7-fold in 0.6 and 2.5 mM Ca2+, respectively, P less than 0.05). 6. I conclude that tolerance to and dependence on morphine are not associated with changes in the availability of Ca2+ for NA-induced contractions of the mouse vas deferens.
authors.affiliation: Departamento de Farmacologia, Universidade Federal de Santa Catarina, Florianópolis, Brasil.
authors.forename: G A
authors.initials: GA
authors.lastname: Rae
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004361:Drug Tolerance; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology*; D014649:Vas Deferens / Q000187:drug effects*
chemical_list: D009020:Morphine; D002118:Calcium; D009638:Norepinephrine