title: Role of calcium in the secretomotor response of the thyroid: effects of calcium ionophore A23187 on radioiodine turnover, membrane potential and fluid transport in cultured porcine thyroid cells.
abstract: The calcium ionophore A23187 (0.1-1 mumol/l) inhibited membrane electrical polarization, uptake of 125I, fluid transport and TSH-stimulated release of radioiodine from the organic pool in follicular cultures of porcine thyroid cells. At higher concentrations (1-30 mumol/l), A23187 promoted release of radioiodine from the organic pool. Stimulation of release of radioiodine from the organic pool by veratridine (a sodium channel agonist, 0.4-1 mmol/l) and A23187 was dependent on the calcium concentration of the medium, while TSH action was independent. Incubation in medium of very low calcium concentration (0.0177 mmol/l) resulted in enhanced release from the organic pool, which was inhibited by TSH (256 microU/ml), A23187 (25 mumol/l) or veratridine (0.5 mmol/l). These data therefore do not support the hypothesis that calcium acts as a mediator of the secretomotor action of TSH, but suggest the possibility of a TSH-induced increase in intracellular calcium as a regulatory negative-feedback mechanism.
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D015232:Dinoprostone; D007424:Intracellular Fluid / Q000378:metabolism*; D007455:Iodine / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D011458:Prostaglandins E / Q000494:pharmacology; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D013972:Thyrotropin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
chemical_list: D011458:Prostaglandins E; D000001:Calcimycin; D014701:Veratridine; D013972:Thyrotropin; D007455:Iodine; D015232:Dinoprostone; D002118:Calcium