Taxol stabilizes [Ca2+]i and protects hippocampal neurons against excitotoxicity

Elevation of intracellular calcium levels [Ca2+]i induces microtubule depolymerization, a process which plays roles in regulation of cell motility and axonal transport. However, excessive Ca2+ influx, as occurs in neurons subjected to excitotoxic conditions, can kill neurons. We now provide evidence that the polymerization state of microtubules influences neuronal [Ca2+]i homeostasis and vulnerability to excitotoxicity. The microtubule-stabilizing agent taxol significantly attenuated glutamate neurotoxicity in cultured rat hippocampal neurons. Experiments in which [Ca2+]i was monitored using the Ca2+ indicator dye fura-2 showed that the elevation of [Ca2+]i induced by glutamate was significantly attenuated in neurons pretreated with taxol. Experiments using selective glutamate receptor agonists suggested that taxol suppressed Ca2+ influx through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors, but not through N-methyl-D-aspartate (NMDA) receptors. Taxol attenuated the neurotoxicity of the microtubule-depolymerizing agent colchicine; colchicine neurotoxicity was, in part, dependent on Ca2+ influx. These findings suggest that microtubules play a role in the mechanism of excitotoxicity and suggest that taxol and related compounds may be useful as antiexcitotoxic agents.