Figure 4.

Calcium-activated Cl${}^{-}$ channels (CaCC) are gated by increasing concentrations of cytosolic Ca${}^{2+}$ and influenced by membrane voltage. The source of Ca${}^{2+}$ may be Ca${}^{2+}$-permeable ion channels located in proximity to CaCCs (not shown) or Ca${}^{2+}$ released from intracellular stores. Stimulation of G$\alpha$${}_{q/11}$-coupled receptors (left) activates phospholipase C (PLC). The subsequent hydrolysis of phosphatitylinositol 1,4, bisphosphate (PIP${}_2$) forms inositiol 1,4,5 trisphosphate (IP${}_3$) and diacylglycerol (DAG). DAG activates protein kinase C (PKC) which influences CaCC function. IP${}_3$ binds to IP${}_3$ receptors located in the membrane of the endoplasmic reticulum (ER) which causes Ca${}^{2+}$ release from the ER. Activation of G$\alpha$${}_{i/o}$-coupled receptors (right) was shown to decrease CaCC currents via an unknown mechanism.