Table 1

Heterotrimeric G protein subtypes and their coupling to some effector systems

Family	Subtype	Action on Effectors	Distribution	Effects
G_sα	α_s	Stimulate all AC isoforms; synergism with forskolin (AC IV, AV, and VI); synergism with Ca²⁺/CaM (AC I, III, and VIII)	Heart, brain, lung neurons, kidney liver, adrenal gland, cerebral cortex	Activate Ca²⁺ channels, cardiac positive inotropy Activate Ca²⁺ channels, contractile proteins
	α_olf	Stimulate AC V, VI, and III	olfactory epithelium	activate Ca²⁺ channels
G_iα	α_il	G_iα1–G_iα3inhibit AC I, V,	Brain, olfactory	Regulate K⁺, Ca²⁺ channels
	α_i2	AC VI (AC I modestly with	(α_i1–α_i3); heart, all	(α_i1, α_i3); inhibit cAMP
	α_i3	Ca²⁺/CaM, poor with G_sα);	tissues (α_i1–α_i3); liver;	synthesis (α_i1–α_i3);
	α_o	inhibit AC I as above	olfactory, neurons	inhibit Ca/CaM actions
	α_τ1	Activate cGMP PDE	Retina rod	Phototransduction
	α_τ2	(α_τ1, α_τ2)	Retina cone	(α_τ1, α_τ2)
	α_z	Inhibit AC I and V	brain, neurons	inhibit cAMP synthesis
G_qα	α_q	Activate PLC-β₁	Neurons, heart	Phototransduction
	α₁₁	Activate PLCs	ubiquitous (α_q, α₁₁)	Mobilize Ca²⁺, IP₃ formation
	α₁₄	(all G_qα)	stroma, epithelium	Activate ion channels
	α₁₅	Activate PLC-β₁	hematopoietic cells	Mobilize Ca²⁺
	α₁₆	Activate PLC-β₁, PLC-β₂	(α₁₅, α₁₆)	Mobilize Ca²⁺
G_α12	α₁₂	Inhibit ACI	Ubiquitous	Regulate Na⁺/K⁺ exchange
	α₁₃	Activate AC	Brain	(α₁₂, α₁₃)
G_βγ complex		Inhibit AC I, stimulate AC II, IV, and VII (with G_sα activation), GRKs, PLC-β₁, PLC-β₂, PLC-β₃, PLA₂	Heart, brain retina, ubiquitous	Activate cardiac K⁺ channel
G_β1–G_β5		Combinations with G_γinhibit AC I and II	Heart (except β₄, β₆) ubiquitous	Additional specificity and selectivity versus G_βγ complex?
G_γ1–G_γ11		Combinations with G_βinhibit AC I and II	Brain (γ2, γ3, γ5, γ7), heart (γ5, γ7) kidney (γ5), liver (γ5), lung (γ5, γ7)	Additional specificity, selectivity versus G_βγ complex?