AJP - Endocrinology and Metabolism, Vol 244, Issue 6 541-E547, Copyright © 1983 by American Physiological Society
Interactions between magnesium and calcium in beta-cell-rich pancreatic islets
P. O. Berggren, P. Bergsten, E. Gylfe, R. Larsson and B. Hellman
Calcium-magnesium interactions, total amounts of intracellular magnesium,
and insulin release were studied in beta-cell-rich pancreatic islets from
ob/ob mice. Mg2+ inhibited the uptake of intracellular 45Ca and insulin
release induced by glucose or high concentrations of potassium. Omission of
Mg2+ from a Ca2+-deficient medium resulted in an increased efflux of 45Ca,
whereas the characteristic glucose inhibition of the efflux was diminished.
After addition of Mg2+ to a Mg2+-depleted medium, the glucose-stimulated
45Ca efflux was markedly reduced. Mg2+ inhibited the basal efflux of 45Ca,
and this effect was preceded by a transient stimulation. Ca2+ but not Mg2+
stimulated 45Ca efflux in a medium depleted of Ca2+, Mg2+, and Na+. The
data indicate that Mg2+ interferes with Ca2+ entry through
voltage-dependent Ca2+ channels. Mg2+ may also inhibit the outward
transport of Ca2+ from the cells at a site different from the Na+-Ca2+
countertransport mechanism. The total amount of intracellular magnesium
remained unaffected by glucose and was not changed unless the ionic
composition of the mediums were changed grossly. Under physiological
conditions it is therefore unlikely that fluctuations in the intracellular
Mg2+ concentration are part of the mechanism by which the functionally
important Ca2+ is regulated.
