Figure 6.
Proposed mechanism for the UVR phototransduction cascade in HEMs. (A) UVR stimulates a G protein–coupled receptor in a retinal-dependent manner, and leads to activation of Gαq/11 and PLCβ, which hydrolyzes PIP2 into DAG and IP3. PIP2 hydrolysis regulates the activity of TRPA1 at the plasma membrane to mediate Ca2+ influx, whereas IP3 activates IP3R to mediate Ca2+ release from intracellular stores. The increase in intracellular Ca2+ leads to early melanin synthesis. (B) Predicted contribution of IP3R- and TRPA1-mediated Ca2+ responses to UVR-induced Ca2+ signaling kinetics. IP3R contributes to the rapid initial increase in Ca2+, whereas TRPA1 contributes to sustained Ca2+ influx.