title: 24R,25-(OH)2 vitamin D3 inhibits 1alpha,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 intracellular calcium initiated by plasma membrane receptors for 1alpha, 25-dihydroxyvitamin D3 (1alpha,25-D3). 24R,25-Dihydroxyvitamin D3 (24,25-D3) alone, in concentrations up to 200 nM, does not cause potentiation of calcium currents in osteoblasts, but it does inhibit the current potentiation by 1alpha,25-D3. To determine how various steroids interact in their potentiation of calcium channels, the action of vitamin D3 analogues and testosterone with calcium channels in the rat osteoblast-like cell line ROS 17/2.8 was investigated. Bath additions of both 1alpha,25-D3 and testosterone at doses below K1/2 (the dose causing 50% left shift in the current-voltage relationship) are additive in their ability to potentiate calcium channels. When 1alpha,25-D3 and testosterone are added together at concentrations that would cause a maximal shift in the current-voltage relationship by each agent alone (Vmax), the effect of these steroids is not additive. Taken together these data suggest one population of calcium channels is activated by 1alpha, 25-D3 or testosterone. The shift in the current-voltage relationship caused by 1alpha,25-D3 is reduced by 1beta,25-dihydroxyvitamin D3 (1beta,25-D3), an agent which is thought to act specifically on the plasma membrane receptor for 1alpha,25-D3, but the potentiation caused by testosterone is not blocked by 1beta,25-D3. However, 24, 25-D3 inhibits the left shift in the peak current-voltage relationship mediated by either 1alpha,25-D3 and testosterone. This result implies that 1) 1beta,25-D3 directly displaces 1alpha,25-D3 but not testosterone from its plasma membrane receptor, and 2) the rapid (in seconds) stimulatory effects of 1alpha,25-D3 and testosterone on calcium channels are mediated by separate plasma membrane receptors for testosterone and 1alpha,25-D3, which are blocked by another receptor for 24,25-D3. The interaction of these three receptors with L-type calcium channels is pertussis toxin-sensitive.
authors.affiliation: Department of Medicine, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: K
authors.initials: K
authors.lastname: Takeuchi
authors.forename: S E
authors.initials: SE
authors.lastname: Guggino
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3 / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000378:metabolism; D002117:Calcitriol / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D012516:Osteosarcoma / Q000378:metabolism*; D037342:Pertussis Toxin; D051381:Rats; D013739:Testosterone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D001464:Barium; D013739:Testosterone; D015650:24,25-Dihydroxyvitamin D 3; D037342:Pertussis Toxin; D002117:Calcitriol