Rapid actions of calcitriol and its side chain analogues CB1093 and GS1500 on intracellular calcium levels in skeletal muscle cells: a comparative study.
1. The ability of synthetic analogues of the secosteroid hormone 1alpha,25-dihydroxy-vitamin-D3 [calcitriol, CT; 1,25(OH)2D3] to exert non-genomic (rapid) effects on target cells has been scarcely studied. To evaluate the pharmacological potential of the CT side-chain analogues CB1093 and GS1500, we compared their fast effects on intracellular calcium concentration ([Ca2+]i) in chick skeletal muscle cells with those elicited by the natural hormone. 2. Both analogues, similarly to CT, specifically induced rapid (30-60 s) and sustained rises in [Ca2+]i levels. CB1093 and GS1500 were more potent than the natural hormone at concentrations as low as 10(-13) M (4.5 fold stimulation) and 10(-12) M (2.5 fold), respectively, whereas higher concentrations (10(-9)- 10(-8) M) of CT were more effective than the analogues in elevating [Ca2+]i. Cyclic AMP was markedly increased by both analogues pointing for a role of this messenger in the fast actions of the synthetic compounds. 3. In Ca2+ free medium CT and analogues elicited a transient elevation in [Ca2+]i. The PLC inhibitors U73122 (2 microM) and neomycin (0.5 mM), as well as depletion of intracellular stores with thapsigargin (1 microM), completely prevented CB1093/GS1500-dependent changes in [Ca2+]i suggesting that, similarly to CT, these analogues mobilized Ca2+ from an IP3/thapsigargin-sensitive store. 4. The voltage-dependent calcium channel (VDCC) blocker nifedipine (2 microM) reduced by 50-60% the influx phase of the [Ca2+]i response to CB1093 and GS1500, indicating that VDCC contributed partially to Ca2+ entry. The Ca2+ readdition protocol suggested that analogue-dependent activation of a SOC entry pathway accounted, to the same extent as for CT, for the remaining non-VDCC mediated Ca2+ influx.
Vazquez
G
G
Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina.
Sellés
J
J
de Boland
A R
AR
Boland
R
R
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000032:analysis; D016257:Fura-2 / Q000032:analysis; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*
D000970:Antineoplastic Agents; C103436:CB 1093; D002120:Calcium Channel Agonists; D015220:Calcium Channels; D005456:Fluorescent Dyes; C120257:GS 1500; D002117:Calcitriol; D002118:Calcium; D016257:Fura-2