Involvement of protein kinase C in the modulation of 1 alpha,25-dihydroxy-vitamin D3-induced 45Ca2+ uptake in rat and chick cultured myoblasts
1996
Vazquez, G. | Boland, A.R. de
The calciotropic hormone 1alpha,25-dihydroxy-vitamin D3 (1,25(OH)2D3) has been shown to stimulate both rat and chick myoblast 45Ca2+ uptake via modulation of dihydropyridine-sensitive L-type calcium channels through phosphorylation by the cAMP/protein kinase A pathway. We further investigated the involvement of protein kinases in 1,25(OH)2D3-signal transduction on cultured myoblasts. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) was found to rapidly stimulate myoblast 45Ca2+ uptake, mimicking 1,25(OH)2D3. The effects of PMA were time- (1-5 min) and dose (50-100 nM)-dependent, were mimicked by 1,2-dioctanoylglycerol (DOG) and were specific, since the inactive analogue 4alpha-phorbol was without effect. Analogously to the hormone, PMA-enhanced 45Ca2+ uptake was suppressed by the Ca2+-channel blocker nifedipine (5 micromolar). 1-(5-isoquinolynsulfonyl)-2-methylpiperazine (H-7), a PKC inhibitor, and down-regulation of PKC by prolonged exposure to PMA (1 micromolar, 24 h), abolished both PMA and hormone effects on rat and chick cells. As in chick myoblasts, 1,25(OH)2D3 activated PKC in rat myoblasts, with translocation of activity from the cytosol to the cell membrane. Treatment of myoblasts with PMA (100 nM) plus 1,25(OH)2D3 (1 nM) greatly potentiated 45Ca2+ uptake than either agent alone. PMA also increased myoblast cAMP content. These results suggest the involvement of PKC in the mechanism by which 1,25(OH)2D3 rapidly stimulates calcium uptake in both mammalian and avian myoblasts.
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