Figure 2.

Influence of ER Ca²⁺ release on synaptic vesicle (SV) release and neurotransmission. (A) Action potentials are propagated through axons. Depolarization of presynaptic membrane activates voltage-gated Ca²⁺ channels (VGCCs), which causes Ca²⁺ to enter the synapse. ER Ca²⁺ release contributes to cytosolic [Ca²⁺], which influences release of neurotransmitter-laden SVs. (B) ER Ca²⁺ release, whether increased or decreased, affects the presynaptic cytosolic [Ca²⁺]. The presynaptic cytosolic [Ca²⁺] scales linearly upon activation of VGCCs. The magnitude of SV release obeys a 4th power relationship with presynaptic cytosolic [Ca²⁺], allowing small elevations in [Ca²⁺] to cause large increases in neurotransmitter release (inset).