Nongenomic actions of the steroid hormone 1α25‐dihydroxyvitamin D₃

AbstractRecent studies indicate that the vitamin D hormone, 1α,25‐Dohydroxyvitamin D3 exerts rapid effects (seconds to minutes) in a variety of cell types. These rapid nongenomic actions in osteoblasts include effects on membrance voltage‐gated calcium chananels, phosphlipase C activity, and the sodium/dydrogen antiport. Since the rapid effects occur in osteoblasts that lack the neclear vitamin D receptor, it is postulated that the nongenomic responses to the hormone reflect interaction with a separate, membrane localized signalling system. Preliminary studies demonstrate the presence of a receptor on the membranes of osteoblasts that lack the neclear vitamin D. This membranes receptors recognizes 1 a, 25‐dihyrooxyvitamin D3 and its inaction 1β epimer, but not 25‐hydrovitamin D3. These rapid nongenomic actions generated by interaction with the membrane receptor modulate the effect of the hormone on gene transcription. Thus, the rapid nongenomic pathway may play a regulatory function in modulating the genomic pathways affected by 1 a 25‐dihydroxyvitamin D3.