Relationship between synaptosomal calcium uptake and antinociceptive action of morphine.

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Abstract
The relationship between inhibition of 45Ca2+ uptake and the antinociceptive action induced by morphine and the effects of papaverine and 1,1-diphenyl-3-peridinobutanol hyrdochloride (Aspaminol) on both these actions of morphine were studied [in rats]. Addition of these drugs in the incubation medium significantly inhibited Glu-stimulated synaptosomal 45Ca2+ uptake. The inhibition curves of morphine and Aspaminol on Glu-stimulated synaptosomal 45Ca2+ uptake were linear, but that of papaverin was not. The inhibition of morphine on synaptosomal 45Ca2+ uptake was reversed by addition of naloxone. The inhibition of synaptosomal 45Ca2+ uptake induced by morphine was increased by the simultaneous addition of Aspaminol, but the inhibition induced by both morphine and papaverine was not increased to more than that by papaverine alone. Since morphine-antinociception was potentiated by Aspaminol and blocked by papaverine the inhibition of synaptosomal Ca uptake evidently plays an important role in the production of morphine-antinociception. Since the inhibition of synaptosomal 45Ca2+ uptake by morphine was less than that by both Aspaminol and papaverine, and papaverine blocked morphine-antinociception, notwithstanding that 10-4 M of papaverine alone completely inhibited Glu-stimulated 45Ca2+ uptake into synaptosomes, it may be difficult to account for the antinociceptive action of morphine by the inhibition of 45Ca2+ uptake only.