Effects of opiates on high-affinity Ca2+,Mg2+-ATPase in brain membrane subfractions.
The effect of a single administration of morphine sulfate (15 mg/kg, s.c. or 30 mg/kg, i.p., 30 min) on Ca2+-stimulated Mg2+-dependent ATPase activity was investigated in synaptosomal plasma membranes (SPM) prepared from rat cortex. Morphine produced a significant decrease in Ca2+,Mg2+-ATPase activity in synaptosomal fractions (SPM 1 + 2) known to contain a high density of opiate receptors and calmodulin-dependent Ca2+,Mg2+-ATPase. However, in another subpopulation (SPM 3) that contains fewer opiate receptors and less enzyme activity, no such decrease in the enzyme activity was observed after the opiate administration. The decrease in Ca2+,Mg2+-ATPase activity seen in SPM 1 + 2 was specifically antagonized by the opiate antagonist naloxone hydrochloride (2 mg/kg, s.c.) when given 15 min before morphine administration. Mg2+-ATPase was not altered either by morphine or by a naloxone-morphine combination. These findings give further evidence for the role of intracellular Ca2+ in mediating many of the acute effects of opiates.
D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000648:ultrastructure; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007700:Kinetics; D008566:Membranes / Q000201:enzymology; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats
D009294:Narcotics; D009270:Naloxone; D009020:Morphine; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases