INVOLVEMENT OF PROTEIN-KINASE-C IN 1,25(OH)(2) VITAMIN-D-3 REGULATIONOF CALCIUM-UPTAKE BY CULTURED MYOCYTES

1,25-Dihydroxyvitamin D-3 [1,25(OH)(2)D-3] produces an acute stimulati on of calcium influx in cultured chick embryo myocytes through activat ion of voltage-gated Ca2+ channels and involvement of cyclic AMP-depen dent protein kinase A (PKA). To investigate the participation of prote in kinase C (PKC) in this hormone-induced response, calcium uptake was measured in myocytes treated with PKC activators 12-O-tetradecanoyl p horbol 13-acetate (TPA, 50 nM) or 1,2- dioctanoyl-rac-glycerol (DOG, 5 0 mu M). TPA and DOG decreased Ca-45(2+) uptake 37% below control cult ures. Contrarily, the PKC inhibitors H-7, and staurosporine increase m yocyte Ca2+ uptake 51% and 54%, respectively. In addition, PKC activit y was augmented in cytosol (39%) and membranes (31%) of myocytes after 5 min of treatment with 0.1 nM 1,25(OH)(2)D-3. Likewise, the hormone induced a fast biphasic formation of diacylglycerol, the natural PKC a ctivator, peaking at 30 s (26%) and 3 min (39%). On the other hand, th e stimulation of Ca2+ uptake induced by compound H-7 as well as 1,25(O H)(2)D-3 was completely abolished with a specific PKA inhibitor. H-7 a lso produced an increase in cAMP levels (172%) and PKA activity (204%) . These results suggest the participation of PKC in 1,25(OH)(2)D-3 reg ulated calcium influx in heart cells and the operation of a cross-talk mechanism between the PKC and PKA pathways.