Figure 3. Relationship between the magnitude of presynaptic Ca²⁺ entry and the release of neurotransmitter.

Ai, a Ca²⁺ transient in the reticulospinal axon (measured as in Fig. 2) was blocked by 30 μm Ni²⁺. Aii, an EPSC was recorded from a ventral horn neuron by extracellularly stimulating the reticulospinal axons in the ventro-medial tracts. The compound EPSC was also blocked by 30 μm Ni²⁺. Bi, relationship between evoked EPSC amplitude and presynaptic Ca²⁺ transient amplitude. Normalized EPSCs (n= 3) are plotted against normalized Ca²⁺ transients (n= 3) at the same Ni²⁺ concentration. Bii, the relationship shown in Bi became linear when the EPSC amplitude was plotted against the cube of the Ca²⁺ transient amplitude at the same [Ni²⁺]_o.