levoxadrol and metaphit

The ion channel probe phencyclidine [1-(1-phenylcyclohexyl)piperidine; PCP] selectively inhibited aggregation, secretion and ultrastructural changes in platelets induced by adrenaline, but did not affect activation induced by other common platelet agonists such as alpha-thrombin, ADP, collagen or ionophore A23187. [3H]PCP bound to platelets with high affinity (Kd 134 +/- 33 nM; 3600 +/- 1020 sites/platelet), as did the thienyl analogue [3H]TCP (1-[1-(2-thienyl)cyclohexyl]piperidine). PCP binding to platelets was increased 3-4-fold in N-methylglucamine buffer in the absence of Na+ ions. Binding was unaffected by haloperidol and was only weakly inhibited (EC50 10-20 microM), without significant stereoselectivity by the two sets of stereoselective ligands, dexoxadrol/levoxadrol and (+)MK801/(-)MK801. Binding of PCP was not competed for by adrenaline or yohimbine. Only the high-affinity binding of [3H]PCP to platelets was blocked by prior treatment of the platelets with the covalent affinity probe Metaphit, and these platelets no longer aggregated in response to adrenaline although they responded normally to alpha-thrombin, ADP and collagen. These results suggest that platelets contain high-affinity receptors for PCP that can modulate adrenaline-induced platelet activation.

Topics: Binding, Competitive; Blood Platelets; Cells, Cultured; Chromatography, Gel; Cyclic AMP; Dioxolanes; Dizocilpine Maleate; Epinephrine; Humans; Phencyclidine; Piperidines; Platelet Activation; Receptors, Neurotransmitter; Receptors, Phencyclidine

The interactions of phencyclidine (PCP) and related agonists with putative receptor blockers were studied on cerebellar Purkinje neurons using electrophysiological techniques. Depressions induced by PCP or dexoxadrol, a sigma receptor agonist, were markedly antagonized by the PCP receptor antagonist metaphit, which acylates PCP receptors via its isothiocyanate moiety. Conversely, the depressant effect of levoxadrol, the (-) isomer of dexoxadrol, was not affected by metaphit. Further evidence that metaphit's specific antagonism of dexoxadrol- and PCP-mediated depressions was derived from data showing that drugs which respectively acylate mu and delta opioid receptors, benzimidazole isothiocyanate and fentanyl isothiocyanate, do not antagonize the actions of either PCP or dexoxadrol. Moreover, tyramine, which like PCP acts as an indirect norepinephrine agonist, is not antagonized by metaphit. These observations support the concept that metaphit causes a pharmacologically specific and irreversible antagonism of the effects of both PCP and dexoxadrol in the cerebellum. Thus, the electrophysiological mechanisms of PCP actions are similar to those triggered by sigma opioid agonists in this brain area.

Topics: Animals; Cerebellum; Dioxolanes; Drug Interactions; Electrophysiology; Isomerism; Male; Phencyclidine; Piperidines; Purkinje Cells; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, sigma; Substrate Specificity