A neurotoxin selectively blocks calcium channels at the presynaptic terminal of a neuron. Which effect will immediately dominate at the synapse?

💡 Explanation

Blocking calcium channels at the presynaptic terminal inhibits calcium influx, a crucial step for neurotransmitter release. Vesicle fusion with the presynaptic membrane is calcium-dependent; therefore, blocking calcium influx reduces the neurotransmitter vesicle fusion rate, rather than increasing action potential frequency or receptor binding, because neurotransmitter release is prevented.

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