Figure 16.

A scheme to illustrate spatial relationships among ryanodine receptor, N-type Ca²⁺ channel, BK, and SK channels. [Ca²⁺]_D means the [Ca²⁺]_i in the Ca²⁺ microdomain closed to the orifices of N-type Ca²⁺ channel and ryanodine receptor Ca²⁺ release channel. [Ca²⁺]_BK and [Ca²⁺]_SK are the Ca²⁺ concentrations involved in the activation of BK and SK channels, respectively. Arrows indicate the pathways of Ca²⁺ entering via N-type Ca²⁺ channels or ryanodine receptors. Numbers with percents indicate the fraction of the contribution of CICR to the activation of BK or SK channel involved in a single AP generated sparsely, whereas the numbers in parentheses are those during a sustained high frequency induction of APs.