1α,25-dihydroxy-vitamin-D3-induced store-operated Ca2+ influx in skeletal muscle cells -: Modulation by phospholipase C, protein kinase C, and tyrosine kinases

In skeletal muscle cells the steroid hormone 1 alpha,25-dihydroxy-vitamin-D-3 (1,25(OH)(2)D-3) nongenomically promotes Ca2+ release from intracellular stores and cation influx through both L-type and store-operated Ca2+ (SOC) channels. In the present work we evaluated the regulation and kinetics of the 1,25(OH)(2)D-3-stimulated SOC influx in chick muscle cells, Stimulation with 10(-9) M 1,25(OH)(2)D-3 in Ca2+-free medium resulted in a rapid (40-60 s) but transient [Ca2+](i) rise, which correlated with sterol-dependent inositol 1,4,5-trisphosphate production. The SOC influx stimulated by the hormone was insensitive to both L-type channel antagonists and polyphosphoinositide-specific phospholipase C (PPI-PLC) inhibitors but was fully inhibitable by La3+ and Ni2+. PPI-PLC blockade prior to 1,25(OH)(2)D-3 stimulation suppressed both the [Ca2+](i) transient and the SOC influx. 1,25(OH)(2)D-3-induced SOC entry was markedly increased after 3 min of treatment (30% above basal) and then rapidly reached a steady-state level, The sterol-stimulated SOC influx was prevented by protein kinase C and tyrosine kinase inhibitors but unaffected by blockade of the protein kinase A pathway. None of these inhibitors altered the thapsigargin-induced SOC entry, suggesting the operation of a signaling mechanism different from that for sterol-dependent SOC influx, The present results indicate that 1,25(OH)(2)D-3-induced activation of PPI-PLC is upstream to Ca2+ influx through SOC channels and point for a role of both protein kinase C and tyrosine kinases but; not protein kinase A in the regulation of the sterol-dependent SOCE pathway.