Molecular Pharmacology, Vol 14, 448-453, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Effects of Morphine on the Incorporation of [¹⁴C]Serine into Phospholipid via the Base-Exchange Reaction

¹ Langley Porter Neuropsychiatric Institute and Departments of Pharmacology and Psychiatry, University of California, San Francisco, California 94143

The effects of morphine on the incorporation of [¹⁴C]serine into phospholipid via the base-exchange reaction were examined using washed brain microsomal membranes as the enzyme source. The addition of morphine in vitro increased the basal rate (no added Ca⁺⁺) of [¹⁴C]serine exchange, with the maximum increase occurring at 10 µM. This concentration of morphine also increased the Ca⁺⁺-stimulated exchange at Ca⁺⁺ concentrations of 10, 15, and 20 mM but not 5, 25, or 30 mM. These morphine effects in vitro were blocked by naloxone. Both acute and chronic prior treatment with morphine decreased the basal rate of [¹⁴C]serine exchange. However, chronic but not acute morphine treatment significantly increased the Ca⁺⁺-stimulated exchange of [¹⁴C]serine at all Ca⁺⁺ concentrations tested (2.5-30 mM). In contrast, chronic morphine treatment slightly but significantly stimulated [¹⁴C]ethanolamine exchange at one Ca⁺⁺ concentration (2.5 mM) and decreased [¹⁴C]choline exchange at all Ca⁺⁺ concentrations tested. Possible mechanisms underlying these various changes are discussed.

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ACKNOWLEDGMENTS The authors acknowledge the editorial and typing assistance of Barbara Halperin and Kaye Welch.