Extracellular calcium potentiates the inhibitory effects of magnesium on parathyroid function in dispersed bovine parathyroid cells

Abstract We studied the relative potencies of extracellular calcium and magnesium in inhibiting PTH release and dopamine-stimulated cAMP accumulation in dispersed bovine parathyroid cells. At 1.0 mmol/L calcium, PTH release was half-maximally suppressed by 1.8 mmol/L magnesium. At calcium concentrations in the subphysiologic range (≤ 100 μmol), on the other hand, magnesium was markedly less potent as an inhibitor of these parameters. With 1.0 mmol/L EGTA and no added calcium (free calcium −8 mol/L), half-maximal inhibition of PTH release accumulation occurred at 10 to 15 mmol/L magnesium. Extracellular calcium also markedly potentiated the inhibitory effects of extracellular magnesium on dopamine-stimulated cyclic adenosine monophosphate (cAMP) accumulation. Low magnesium concentrations (