Figure 7. Model for the non-genomic actions of 1,25(OH)2D. 1,25(OH)2D binds to a putative membrane receptor. This leads to activation of a G protein (GTP displacement of GDP and dissociation of the β and γ subunits from the now active α subunit). Gα -GTP activates phospholipase C (PLC) (β or γ) to hydrolyze phosphatidyl inositol bis phosphate (PIP2) to inositol tris phosphate (IP3) and diacyl glycerol (DG). IP3 releases calcium from intracellular stores via the IP3 receptor in the endoplasmic reticulum; DG activates protein kinase C (PKC). Both calcium and PKC may regulate the influx of calcium across the plasma membrane through various calcium channels including L-type calcium channels.