Figure 13.

Downstream pathways and effector channels for Gq/11, Gs, and Gi protein coupled receptors. Gs protein coupled receptors (GsPCRs) and Gq/11 protein coupled receptors (GqPCRs) are in general excitatory systems, and Gi protein coupled receptors (GiPCRs) are inhibitory systems. Both GsPCRs and GiPCRs regulate AC, cAMP, and PKA, and GqPCRs facilitate Ca²⁺ release from Ca²⁺ store and protein kinase C (PKC). These second messenger proteins up- and downregulate open probability of several voltage-dependent cation channels. PIP2 (phosphatidylinositol 4,5-biphosphate), PLC (phospholipase C), IP3 (inositol-1,4,5-trisphosphate), DAG (diacylglycerol), PKC, AC (adenylyl cyclase), cAMP (cyclic AMP), PKA (protein kinase A), I_CAN (calcium-activated nonspecific cation current), I_h (hyperpolarization activated non-selective cation channels), GIRK (G protein coupled inward rectifier K⁺ channels), KCa²⁺ (Ca²⁺-activated K⁺ channels), Cav (voltage-dependent Ca²⁺ channels), Nav (voltage-dependent Na⁺ channels), M-current (muscarinic receptor activated K⁺ channels), and K_ATP (ATP-sensitive K⁺ channels).