24R,25-(OH)2 Vitamin D3 Inhibits 1α,25-(OH)2 Vitamin D3 and Testosterone Potentiation of Calcium Channels in Osteosarcoma Cells

Abstract

Calcium influx via L-type calcium channels in osteoblast cells causes a rapid (in seconds) elevation in intra-A newly described function of 1␣,25-D 3 1 and its analogues is the rapid (in seconds) regulation of intracellular calcium concentration, first reported in chicken duodenum (1) and later in bone osteoblast cells (2-12). It has been documented by patch clamp recordings of whole-cell barium currents (2, 3), by 45 Ca 2ϩ uptake (5, 7), and by fluorescence measurements of intracellular calcium, using the calcium indicator acetoxymethyl Quin2 (10), that 1␣,25-D 3 (2) and other vitamin D 3 metabolites (3,5,7,8,(12)(13)(14) stimulate calcium influx into rat osteosarcoma cells (2,3,5,7,8,12,14) and human and rat osteoblasts (4, 6) in primary culture. Guggino et al. (15) and Caffrey and FarachCarson (2) have shown the presence of L-type calcium channels in ROS 17/2.8 osteoblast-like osteosarcoma cells. These channels, first described in nerve, brain, cardiac and skeletal muscle, are voltage-dependent, conduct barium and calcium, and are blocked by the dihydropyridine antagonist nitrendipine, blocked by the phenylalkylamine antagonist verapamil, and stimulated by the dihydropyridine agonist BayK 8644 (16 -19 influx into ROS 17/2.8 cells yet bound poorly to the nuclear VDR of ROS 17/2.8. Yukihiro et al. (3) reported that the potentiation of calcium channels by these analogues is not compatible with VDR being involved in signal transduction because the structural features like double bonds at carbon 16 and 23 (25-hydroxy-16,23E-diene-D 3 ) (Fig. 1, A-C) or addition of a hydroxyethyl group at the 1-carbon position (1-(1Ј-hydroxyethyl)-25-hydroxy-D 3 ), which cause activation of rapid calcium signal transduction (5), virtually eliminate binding to VDR (3).Although it has been reported that 1␣,25-D 3 and several analogues potentiate calcium channel openings, some vitamin D 3 analogues with inhibitory effects have also been reported.

Antagonistic effects of 24R,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 on L-type Ca2+ channels and Na+/Ca2+ exchange in enterocytes from Atlantic cod (Gadus morhua)

“…L-type Ca 2+ channels as a target for 24R,25(OH) 2 D 3 action have previously been reported in ROS 17/2·8 cells (Caffrey & Farach-Carson 1989, Yukihiro et al 1994, Takeuchi & Guggino 1996 and UMR 106 cells (Li et al 1997). In ROS 17/2·8 cells, 24R,25(OH) 2 D 3 decreases the entry of calcium-45 and inhibits voltage-gated Ca 2+ channels at positive membrane potentials (Caffrey & Farach-Carson 1989, Yukihiro et al 1994.…”

“…This is in line with the findings of previous studies and seems to indicate a general phenomenon for cells in different Ca 2+ regulatory organs. In the chicken (deBoland & Norman 1990) and rat (Massheimer et al 1994) channels has also been demonstrated in osteoblasts (Caffrey & Farach-Carson 1989, Yukihiro et al 1994, Takeuchi & Guggino 1996, Li et al 1997 (Takeuchi & Guggino 1996). The physiological relevance of rapid, non-genomic effects on intestinal Ca 2+ transport and on mineralization processes in bone may be to enable a rapid regulation of free Ca 2+ concentrations in the blood and extracellular fluids.…”

“…In ROS 17/2·8 cells, 24R,25(OH) 2 D 3 decreases the entry of calcium-45 and inhibits voltage-gated Ca 2+ channels at positive membrane potentials (Caffrey & Farach-Carson 1989, Yukihiro et al 1994. Furthermore, 24R, 25(OH) 2 D 3 antagonizes an increased opening of L-type Ca 2+ channels evoked by 1,25(OH) 2 D 3 and testosterone (Takeuchi & Guggino 1996). In UMR 106 cells, Li et al (1997) (Nemere et al 1994, Larsson 1999, chick tibial fracture-healing callus (Seo et al 1996, Kato et al 1998) and chondrocytes (Pedrozo et al 1999), suggesting that the rapid actions of 24R,25(OH) 2 D 3 are mediated through a membrane-associated receptor.…”

Biochemical characterization and purification of a binding protein for 24,25-dihydroxyvitamin D3 from chick intestine

“…24,25(OH) 2 D 3 has not been as widely studied, perhaps because of the perception that it is an inactivation product. However, a growing body of literature has indicated that 24,25(OH) 2 D 3 has important effects in development (Henry & Norman 1978), bone (Sömjen et al 1983, Lidor et al 1987, Schwartz et al 1988, Swain et al 1993, Khoury et al 1995, Yukihiro et al 1994, Takeuchi & Guggino 1996, Ono et al 1996, Seo & Norman 1996, Kato et al 1998, and parathyroids (Carpenter et al 1996). More recently (Nemere 1996a(Nemere , 1999, it has been demonstrated that in chick intestine, 24R,25(OH) 2 D 3 inhibits the rapid stimulation of calcium transport mediated by 1,25(OH) 2 D 3 .…”

Effect of 24,25-dihydroxyvitamin D3 on localization of catalase in chick enterocytes

“…While 1,25-dihydroxyvitamin D 3 stimulates the rapid transport of calcium and phosphate in both perfused chick duodenal loops and isolated enterocytes, 24,25-dihydroxyvitamin D 3 inhibits such stimulation [3,4]. In osteoblasts and osteosarcoma cells, 1,25(OH) 2 D 3 has been found to have a rapid effect on calciumchannel-opening, while 24,25(OH) 2 D 3 was found to inhibit this nonnuclear effect [5][6][7]. In chick intestinal cells, 1,25(OH) 2 D 3 has been found to have an acute, non-nuclear effect on phosphate transport, and 24,25(OH) 2 D 3 has been found to inhibit the reaction [8], with no effect on parathyroid hormone (PTH) stimulated phosphate transport [9].…”