Figure 10. Scheme illustrating the effects of depolarization on IP₃-sensitive Ca²⁺ stores in cultured hippocampal neurones.

A, at rest, the Ca²⁺ stores are functionally empty, with little or no release in response to IP₃ formation. B, in the presence of a modest depolarization Ca²⁺ influx via L-type VGCCs loads the Ca²⁺ stores and allows a strong Ca²⁺ signal on activation of IP₃ receptors. See text for further details.2