ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Parathyroid hormone (PTH) increases renal calcium absorption exclusively in cortical thick limbs and distal tubules. Lack of sufficient tissue has precluded detalled biochemical study of the mechanisms responsible for the hypercalcemic effect of PTH. Therefore, we assessed PTH action on calcium transport in Madin-Darby canine kidney (MDCK) cells, a cell line expressing distal characteristics, to determine its suitability as a model for analyzing PTH action. Calcium transport across MDCK cells grown to confluence on porous filters was measured at 37°C in Ussing chambers. Mucosal-to-serosal calcium fluxes (JCa, mol/min cm-2 × 10-9) were measured with 45Ca at -3, -1, 5, 10, and 20 min; agonist was added at 0 min. Basal JCa averaged 0.98. PTH at 0.2 μM increased JCa by 12% (P 0.05) and 1 μM PTH by 70% (P0.01). Calcitonin (1 μM) had no effect on JCa. The fact that high concentrations of dibutyryl cAMP (1 mM) and forskolin (10 μM) increased JCa by only 37% and 22%, respectively, suggested that cAMP-independent mechanisms may participate in PTH-stimulated JCa. Therefore we examined the effect of other putative second messengers. In the presence of 2 mM external [Ca], 10 nM A23187 increased JCa by 88%, and 10 μM A23187 increased JCa by 121%. Addition of 10 μM phorbol 12-myristate 13-acetate (PMA) increased JCa by 60%. We conclude that: (1) PTH specifically stimulates unidirectional calcium absorption in MDCK cells; (2) both adenylate cyclasecoupled and calcium-coupled receptors may participate in signaling the response to PTH; and (3) confluent MDCK cells represent a useful experimental model for elucidating the biochemical mechanisms involved in the renal hypercalcemic action of PTH.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041390113
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