title: Extracellular Ca2+ sensing in C-cells and parathyroid cells.
abstract: An essential function of C-cells and parathyroid cells is to monitor the extracellular Ca2+ concentration. The Ca(2+)-dependent secretion of calcitonin (CT) and parathyroid hormone is known to be mediated by corresponding changes in the intracellular Ca2+ concentration. To address the question of whether Ca2+ influx through voltage-dependent Ca2+ channels couples the extracellular to the intracellular Ca2+, we applied the patch clamp technique to C-cells of the rMTC 44-2 cell line and to parathyroid cells of the PT-r cell line. The rMTC cells displayed dihydropyridine-sensitive, voltage-dependent, high-threshold Ca2+ channels which allowed ion influx even at the resting potential of about -40 mV. Increases of the concentration of the extracellular divalent cation or adding the Ca2+ channel agonist Bay K 8644 stimulated the steady state ion influx. In contrast, PT-r cells exhibited only fast inactivating, low-threshold Ca2+ channel currents with no steady state conductivity for Ca2+ at the resting potential of around -40 mV. We conclude that dihydropyridine-sensitive Ca2+ channels allow steady state transmembranous Ca2+ influx in C-cells, thereby increasing the cytosolic Ca2+ and CT secretion. Parathyroid cells, however, lack long-lasting Ca2+ channel currents and obviously sense the extracellular Ca2+ concentration by other mechanisms.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002277:Carcinoma / Q000378:metabolism*; D002478:Cells, Cultured; D005110:Extracellular Space / Q000378:metabolism*; D017275:Isradipine / Q000494:pharmacology; D008564:Membrane Potentials; D010280:Parathyroid Glands / Q000378:metabolism*; D051381:Rats; D013964:Thyroid Neoplasms / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002118:Calcium; D017275:Isradipine