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Endocrinology, Vol 107, 1007-1013, Copyright © 1980 by Endocrine Society

ARTICLES

Calcium and pancreatic beta-cell function. IX. Demonstration of lanthanide-induced inhibition of insulin secretion independent of modifications in transmembrane Ca2+ fluxes

PR Flatt, PO Berggren, E Gylfe and B Hellman

beta-Cell-rich pancreatic islets were microdissected from noninbred ob/ob-mice and used to examine the mode of action of trivalent lanthanide ions on insulin secretion. La3+, Sm3+, and Tm3+ were equally effective inhibitors of basal and glucose-stimulated insulin release. As indicated by perifusion experiments with Tm3+, the inhibitory action was prompt, sustained, and readily reversible. Despite the similarities among the lanthanides in inhibiting insulin secretion, these cations differed considerably in their ability to impair transmembrane 45Ca fluxes. Using 10 different members of the lanthanide series, it was possible to demonstrate that their effectiveness to inhibit 45Ca uptake increased with ionic radius. La3+ markedly inhibited intracellular uptake and superficial binding of 45Ca at both 3 and 20 mM glucose. However, Tm3+ failed to affect intracellular 45Ca uptake and only reduced superficial binding of 45Ca at 3 mM glucose. In efflux experiments, Tm3+ did not affect basal or glucose-stimulated 45Ca washout from islets perifused with a medium containing 1.28 mM Ca2+. In a Ca2+-deficient medium, Tm3+ caused a slight transient increase, followed by reduction of 45Ca washout. However, when glucose was omitted, there was a prompt increase in the washout of radioactivity in the presence of Tm3+. Accordingly, the potent inhibitory action of Tm3+ on insulin secretion is not matched by changes in transmembrane Ca2+ fluxes. Since the lanthanides do not penetrate intracellularly, we propose the existence of cationic binding sites in the beta-cell plasma membrane with direct inhibitory effects on insulin secretion.


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C. A. Leech and J. F. Habener
Regulation of Glucagon-Like Peptide-1 Receptor and Calcium-Sensing Receptor Signaling by L-Histidine
Endocrinology, November 1, 2003; 144(11): 4851 - 4858.
[Abstract] [Full Text] [PDF]


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