Figure 10.

A hypothesis for mitochondrial modulation of capacitative Ca²⁺ entry. (A) When Ca²⁺ uptake by mitochondria is blocked, Ca²⁺ accumulates near CRAC channels and inhibits them (bold dashed line). A steady-state [Ca²⁺]_i near the channels is reached as a result of this negative feedback. (B) Sequestration of Ca²⁺ by mitochondria in the absence of export reduces the local [Ca²⁺]_i, thereby partially relieving inactivation of I_CRAC (thin dashed line). At steady state, I_CRAC is larger than in A, but much of the Ca²⁺ from this increased influx is sequestered and hence is not available to enhance global [Ca²⁺]_i. (C) In the presence of normal mitochondrial uptake and release of Ca²⁺, mitochondria redistribute the Ca²⁺ derived from enhanced I_CRAC to distant sites where it can elevate global [Ca²⁺]_i.