Trifluoperazine and dibucaine-induced inhibition of glutamate-induced mitochondrial depolarization in rat cultured forebrain neurones.

1. Glutamate receptor activation has been previously shown to result in mitochondrial depolarization and activation of the mitochondrial permeability transition pore in cultured neurones. In this study, we characterized the effects of two putative permeability transition inhibitors, namely trifluoperazine and dibucaine, on mitochondrial depolarization in rat intact, cultured forebrain neurones. 2. Permeability transition was monitored by following mitochondrial depolarization in neurones loaded with the mitochondrial membrane potential-sensitive fluorescent indicator, JC-1. Trifluoperazine (10 20 microM) and dibucaine (50-100 microM) inhibited or delayed the onset of glutamate-induced permeability transition. 3. We also investigated the effects of trifluoperazine and dibucaine on neuronal recovery from glutamate-induced Ca2+ loads. Trifluoperazine affected Ca2+ recovery in a manner similar to the mitochondrial Na+/Ca2+ exchange inhibitor, CGP-37157, while dibucaine had no apparent effect on Ca2+ recovery. Therefore, inhibition of permeability transition does not appear to be involved in Ca2+ recovery from glutamate-induced Ca2+ loads. 4. Trifluoperazine and dibucaine did not inhibit [3H]-dizocilpine binding at the concentrations that prevented mitochondrial depolarization. 5. These studies suggest that trifluoperazine and dibucaine inhibit permeability transition in intact neurones. Trifluoperazine also appears to inhibit mitochondrial Na+/Ca2+ exchange. These drugs should prove to be valuable tools in the further study of the role of mitochondrial permeability transition in glutamate-induced neuronal death.