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A. G-Protein Coupled Receptor Superfamily

Agonist binding to GPCRs may result in some combination of the following cellular responses: stimulation or inhibition of adenyl cyclase (AC), activation of phospholipase C (PLC) and generation of inositol triphosphate (IP3), activation of protein kinase C (PKC) and an increase in intracellular Ca2+, activation of phospholipase A2 (PLA2) and the generation of the arachidonic acid as second messenger, activate phospholipase D (PLD), act on MAPK pathway through ras signaling cascade and JNK pathway through rac 1/Cdc42 dependent biochemical route, and activation of inwardly rectifying K+ channels or voltage-dependent N-type as well as P/Q type Ca2+ channels (Fig. 12).

Figure 12 Signal transduction mechanisms involved in G-protein coupled receptors (GPCRs). GPCRs of each subfamily may be coupled to different G-proteins and may activate certain pathways. The pathway connecting GPCRs to low molecular weight GTPases and kinase cascades is not yet fully known.

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