Fig. 1. Signal transduction pathways activated by cholinergic agonists in the lacrimal gland. ACh, acetylcholine; M3, muscarinic receptor subtype 3; Gαq, alpha subunit of Gq G protein; PLC, phospholipase C; Pyk2 and Src, nonreceptor tyrosine kinases; raf, mitogen-activated protein kinase kinase kinase; MEK, mitogen-activated protein kinase kinase; MAPK, p44/p42 mitogen-activated protein kinase; IP3, inositol trisphosphate; PKC, protein kinase C; ER, endoplasmic reticulum. (Modified from Dartt DA:Regulation of lacrimal gland secretion by neurotransmitters and the EGF family of growth factors. Exp Eye Res 73:741, 2001, with permission.)