Rapid effects of 1α,25(OH)2D3 in resting human peripheral blood mononuclear cells

The steroid hormone 1 alpha,25(OH)(2)D-3 produces biological responses via both genomic and nongenomic mechanisms. Stimulation of rapid, nongenomic responses by 1 alpha,25(OH)(2)D-3 has been postulated to result from interaction of the ligand with cell membrane 1 alpha,25(OH)(2)D-3 receptors and to involve membrane receptors. We examined the rapid effects of 1 alpha,25(OH)(2)D-3 on calcium mobilization and calcium entry into resting human peripheral blood mononuclear cells isolated from healthy volunteers. We also investigated the possible involvement of purinergic receptors in this action. 1 alpha,25(OH)(2)D-3 induced a time-dependent increase in intracellular calcium concentration ([Ca2+](i)). The initial 1 alpha,25(OH)(2)D-3-stimulated calcium increment was sensitive to thapsigargin (Tg), indicating its origins in calcium release from intracellular stores. 2-Aminoethyldiphenyl berate (2APB), an inhibitor of capacitative calcium entry, caused a significant [Ca2+](i) decrease in human cells treated with 1 alpha,25(OH)(2)D-3. Furthermore, in contrast to observations in osteoblasts and skeletal muscle cells, nifedipine had no effect on 1 alpha,25(OH)(2)D-3-induced calcium entry, suggesting that L-type calcium channels were not implicated in this action. Besides, 1 alpha,25(OH)(2)D-3 prevented the calcium entry induced by 3'-O-(4-benzoyl)benzoyl-adenosine 5'-triphosphate (BzATP), a specific agonist of purinergic P2X(7) receptors. This finding was further confirmed by 1 alpha,25(OH)(2)D-3-induced reduction of BzATP- and 4-aminopyridine (4AP)-stimulated ethidium. bromide fluorescence. The presented results demonstrate, for the first time in healthy, resting human peripheral blood mononuclear cells that 1 alpha,25(OH)(2)D-3 is capable of exerting a rapid, nongenomic effect on [Ca2+](i), while inhibiting of the P2X(7) channel permeability. (C) 2008 Elsevier B.V. All rights reserved.