Model of signalling events in mammalian sperm triggered by a chemotactic ligand produced by the egg
As in the olfactory system, putative sperm chemoreceptors may be coupled with either adenylate cyclase (AC) or phospholipase C (PLC) by the appropriate G protein (G). Stimulation of the receptor by a chemotactic ligand would result in conversion of cellular ATP to cAMP, which would in turn stimulate respiration and motility. In addition, activation of PLC would produce inositol 1,4,5-diphosphate (IP3) from phosphatidylinositol 4,5-bisphosphate (PIP2). IP3-stimulation of IP3 receptors (IP3R) at the proximal midpiece would release calcium from stores in this region, thereby elevating intracellular calcium and modulating motility. Phosphorylation of agonist-occupied chemoreceptors by G-protein receptor kinase 3 (GRK3), followed by β-arrestin2 (βARR) binding, would subsequently desensitize the receptors.