Availability of calcium for noradrenergic contraction of the mouse isolated vas deferens is not altered during tolerance to and dependence on morphine.

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 form control and tolerant/dependent mice (P > 0.05 at any Ca2+ concentration). 3. Omission of Ca2+ from the bathing solution caused a rapid and similar loss of responsiveness to a macimally effective concentration of NA (300 micronM) in both groups (t1/2 0.05). 4. Vasa deferentia obtained from control and tolerant/dependent mice were equally sysceptible to non-competitive antagonism of NA-induced contraction by verapamil (3 to 30 micronM; pD2' values of 5.50 and 5.26, rspectively, (P > 0.05 at any concentration of verapamil). 5. Preparations from tolerant/dependent mice displalyed significant supersensitivity to NA, the magnitude of which was not influence by modifying the Ca2+ concentration in the bathing medium (2.6-and 1.7-fold in 0.6 and 2.5mMCa2+, respectively, P