Effect of magnesium on intracellular calcium levels in parathyroid
cells: evidence for two sensing receptors or two intracellular
pathways?.
Miki, Hitoshi, Peter B. Maercklein, Lorraine A. Fitzpatrick.
Division of Endocrinology and Metabolism, Department of Internal
Medicine, Mayo Clinic and Mayo Foundation, Rochester, MN 55905
APStracts 3:0184E, 1996.
Currently, it remains controversial as to the intracellular mechanisms
coupled to the inhibition of parathyroid hormone (PTH) secretion that
are modulated by extracellular divalent cations. In order to study
mechanisms responsible for regulation of PTH release by cations, we
investigated the effect of magnesium (Mg2+) on intracellular calcium
levels ([Ca2+]i) and PTH secretion in single isolated bovine
parathyroid cells. Addition of 9.0 mM Mg2+ evoked a spike of [Ca2+]i
in approximately 80% of cells in the presence of extracellular
calcium. Mg2+ decreased steady-state [Ca2+]i, which represented
inhibition of influx of extracellular calcium in 13 to 78% of cells.
The percentage of cells that had a decline of steady-state [Ca2+]i
after exposure to Mg2+ was dependent on the extracellular calcium
concentration. The effect of Mg2+ on intracellular calcium response
was dose dependent. Extracellular Mg2+ inhibited PTH secretion in
cells which showed decline of steady-state [Ca2+]i, although cells
which showed a spike after addition of Mg2+ secreted more PTH than
cells which did not show a spike. The spike of [Ca2+]i and decline of
steady-state [Ca2+]i that occurs in response to extracellular Mg2+
may be caused independently by two distinct mechanisms that
differentially regulate secretion of PTH.
Received 11 August 1995; accepted in final form 3 September 1996.
APS Manuscript Number E384-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996