Interaction of extracellular calcium and magnesium in the regulation of cytosolic calcium and PTH release in dispersed bovine parathyroid cells.
We examined the effects of varying the extracellular magnesium (Mg2+) concentration at different extracellular calcium (Ca2+) concentrations on cytosolic Ca2+ and PTH release in dispersed bovine parathyroid cells using the fluorescent, Ca2+-sensitive dye QUIN-2. Raising extracellular Mg2+ from 0.5 to 5 mM produced significant (p less than 0.01) increases in cytosolic Ca2+ from 228 +/- 13 to 306 +/- 15 nM at 0.5 mM extracellular Ca2+ and from 199 +/- 9 to 299 +/- 19 nM at 1.0 mM extracellular Ca2+. The concentration of extracellular Mg2+ which produced half of the maximal increase in cytosolic Ca2+ was significantly higher, however, at 0.5 mM than at 1.0 mM extracellular Ca2+ [3.3 +/- 0.16 (n = 5) vs. 2.0 +/- 0.08 mM Mg2+ (n = 6), p less than 0.01]. High extracellular Mg2+ (5 mM) was associated with a similar inhibition of PTH release at 0.5 and 1.0 mM Ca2+ [67 +/- 2% (n = 4) and 59 +/- 5% (n = 7), respectively], but half-maximal inhibition of secretion occurred at a higher Mg2+ concentration with 0.5 than with 1.0 mM Ca2+ [3.5 +/- 0.43 (n = 4) vs. 2.0 +/- 0.21 mM (n = 5), respectively, p less than 0.01]. In contrast, in cells exposed to subphysiological extracellular Ca2+ concentrations (less than or equal to 10(-6) M), 5 mM Mg2+ had little or no effect on either cytosolic Ca2+ or PTH release. At 10 mM extracellular Mg2+ with less than or equal to 10(-6) M Ca2+, PTH release was inhibited 55 +/- 3% (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D008274:Magnesium / Q000502:physiology*; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*
D010281:Parathyroid Hormone; D008274:Magnesium; D002118:Calcium