Figure 4.

Schematic representation of Ca²⁺/CaM-dependent facilitation of the action of RGS proteins. (a) In a resting (low Ca²⁺) state, the action of RGS is inhibited by PIP₃. (b) Once intracellular Ca²⁺ concentration is elevated, e.g., upon depolarization, Ca²⁺/CaM binds to RGS proteins and reverses the inhibitory effect of PIP₃. (c) Consequently, the G protein cycle is negatively regulated. (d) When the Ca²⁺ concentration decreases to the steady level, CaM dissociates from RGS proteins and their action is once again inhibited by PIP₃.