Vitamin D3 metabolites modulate dihydropyridine-sensitive calcium currents in clonal rat osteosarcoma cells.
A slowly inactivating inward calcium current was identified in the rat osteosarcoma cell line ROS 17/2.8 using a combination of ion flux and electrophysiological techniques. Voltage dependence, dihydropyridine sensitivity, divalent cation selectivity, and single channel properties identified this current as a high threshold, "L-type" calcium current. Ion flux experiments using 45Ca2+ confirmed that calcium uptake through these channel represents a major pathway for calcium entry into osteosarcoma cells. In resting cells, i.e. at negative membrane potentials, stimulation of both calcium current and rapid 45Ca2+ influx could be elicited by concentrations of 1,25-(OH)2-vitamin D3 between 0.1 and 3 nM. At these concentrations, 1,25-(OH)2-vitamin D3 shifted the threshold for activation of inward calcium current to more negative potentials. At higher concentrations (5-10 nM), inhibitory effects became predominant. These opposing effects are functionally similar to those of the dihydropyridine BAY K 8644. Other vitamin D3 metabolites (25-(OH)-D3 and 24,25-(OH)2-D3) exhibited less potent stimulatory effects and greater inhibition of calcium current than 1,25-(OH)2-D3. These results suggest that (i) vitamin D3 acts as a potent modulator of calcium channel function in osteosarcoma cells, and (ii) intracellular Ca2+-dependent signaling processes may be affected acutely by physiological concentrations of vitamin D3 metabolites.
Caffrey
J M
JM
Department of Physiology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030.
Farach-Carson
M C
MC
D015650:24,25-Dihydroxyvitamin D 3 / Q000494:pharmacology*; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002112:Calcifediol / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D004095:Dihydropyridines / Q000494:pharmacology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D012516:Osteosarcoma; D051381:Rats; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D004095:Dihydropyridines; D001464:Barium; D015650:24,25-Dihydroxyvitamin D 3; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium