Aims: 

1a,25(OH)₂D3 has been shown to exert its effects by both genomic and nongenomic mechanisms. We have examined rapid nongenomic effects of the hormone on calcium mobilization and entry through calcium release activated (CRAC) and L-type calcium channels, as well as possible implication of the purinergic P2X₇ receptors in this action.

Methods: 

Human peripheral blood mononuclear cells were obtained from blood samples of healthy volunteers. Intracellular calcium was measured using Fluo 3-AM fluorimetry. P2X₇ pore function was assessed by ethidium bromide confocal imaging.

Results: 

1a,25(OH)₂D3 induced time-dependent rise in [Ca²⁺]_i, which stabilized after 10 min. Sensitivity of the initial 1a,25(OH)₂D3stimulated calcium rise to thapsigargin pointed to its origins in the calcium release from intracellular stores. 2APB, the inhibitor of capacitative entry, but not nifedipine, the L-type calcium channel inhibitor, prevented the hormone-stimulated [Ca²⁺]_i increase. 1a,25(OH)₂D3 inhibited calcium entry stimulated by BzATP, a specific agonist of P2X₇ receptor, while KN-62, a P2X₇ receptor antagonist, had no effect on cells pretreated with 1a,25(OH)₂D3. Furthermore, 1a,25(OH)₂D3 significantly reduced the BzATP stimulated ethidium bromide fluorescence, confirming inhibitory effect of the hormone on calcium influx through P2X₇ channel.

Conclusion: 

Our results demonstrate that 1) 1a,25(OH)₂D3 promotes a two-step calcium response through calcium release from internal stores, followed by store refilling via CRAC, but not L-type calcium channels, while 2) the steroid hormone also induces a nongenomic inhibitory effect on Ca²⁺ entry and the permeability through pore-forming P2X₇ receptor. Supported by Grants No APVT-21-033002 & No APVT-21-019702.