Neurobiochemical evidence for calcium-induced depolarization of EGTA-pretreated hippocampal synaptosomes.

The neurochemical effects of calcium were determined in hippocampal cholinergic synaptosomes which had been prepared and preincubated in calcium-free medium containing 50 microM EGTA. Calcium (and barium) reversibly stimulated [3H]acetylcholine release and produced a long-lasting elevation of high-affinity [3H]choline uptake. Both effects were blocked by omega-conotoxin and substantially reduced by tetrodotoxin. Together, these data indicate that calcium causes membrane depolarization and is associated with opening of voltage-gated sodium channels in EGTA-pretreated synaptosomes.