Identification of calcium channels involved in neuronal injury in rat hippocampal slices subjected to oxygen and glucose deprivation.
Small DL., Monette R., Buchan AM., Morley P.
The presynaptic Ca2+-influx affecting glutamate release during neuropathological processes is mediated via voltage-sensitive calcium channels (VSCCs). There is controversy, however, over the fractional contribution of the specific channel types involved. We have addressed this by investigating the protective effects of various VSCC blockers on oxygen and glucose-deprived rat hippocampal slices. The viability of treated and non-treated slices was assayed electrophysiologically by measuring the evoked population spike (PS) amplitude in the stratum pyramidale of the CA1 region and by imaging slices loaded with fluorochrome dyes specific for dead (ethidium homodimer) and live (calcein) cells using confocal microscopy. PS amplitudes were significantly (P < 0.01) depressed from 4.4 +/- 0.2 mV (n = 38) to 0.2 +/- 0.1 mV (n = 40) after the deprivation insult. Responses from deprived slices treated with omega-conotoxin MVIIC (100 nM; 4.2 +/- 0.5 mV; n = 20) were not significantly different from control, non-deprived slice responses. In contrast, deprived slices treated with either L-type (0.1 or 1 microM nimodipine) or N-type (0.1 or 3 microM omega-conotoxin MVIIA) blockers showed no significant protection. The viability of CA1 neurons as revealed by the fluorescence live/dead confocal viability assay was consistent with the electrophysiological measurements. By comparison with previous studies using P- and Q-type blockers to attempt neuroprotection against the same deprivation insult, the rank order in which specific Ca2+-channel types contribute to neuronal death due to oxygen and glucose deprivation was determined to be Q > N > P > L.