Abstract
The novel kappa agonist U50-488H in vitro produced a concentration-dependent decrease (0.25 – 25 μM) in [ 3H]nimodipine binding in neuronal P 2 fraction from rat brain cortex. Kinetic analysis indicates the decrease in binding results from a reduced B max with no change in affinity (K d). The kappa antagonist, MR2266, blocked the decrease in [ 3H]nimodipine binding to membrane fractions. At equimolar concentrations (25 μM), morphine in vitro had no effect on [ 3H]nimodipinebinding, while U50-488H demonstrated potent inhibition. Further kinetic analysis indicates that the IC 50 for U50-488H is (0.5 – 0.7 μM) and a Dixon plot for K I was found to be 1.5 – 1.7 μM. These results suggest that kappa opiate receptors may be coupled to dihydropyridine receptors and as a result modulate Ca ++ entry and neurotransmitter release in brain neurons.
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