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Endocrinology, Vol 128, 2931-2936, Copyright © 1991 by Endocrine Society

ARTICLES

Effects of the lectin concanavalin-A on the regulation of second messengers and parathyroid hormone release by extracellular Ca2+ in bovine parathyroid cells

G el-Hajj Fuleihan, C Katz, O Kifor, R Gleason and EM Brown
Endocrine-Hypertension Unit, Brigham and Women's Hospital, Boston, Massachusetts 02115.

The lectin Concanavalin-A (Con-A) binds to cell surface carbohydrate- containing moieties and modulates the function of a variety of glycoprotein receptors. Since extracellular calcium (Ca2+) may regulate parathyroid function by a receptor-like process, we examined the effects of Con-A on various aspects of Ca(2+)-regulated parathyroid function. We recently showed that Con-A significantly reduces the inhibitory effects of high Ca2+ on dopamine as well as isoproterenol- and forskolin-stimulated cAMP accumulation. In our present studies Con- A similarly reduced the inhibitory effect of 2.0 mM Ca2+ on PTH release from 60 +/- 6% to 40 +/- 6% and increased the set-point for Ca(2+)- regulated PTH release from 1.25 to 1.8 mM. This effect was dose dependent. Con-A also inhibited the Ca(2+)-stimulated accumulation of inositol phosphates by 50-60% in association with a marked reduction in the high Mg(2+)-evoked spike in cytosolic Ca2+ as well as a significant decrease in the sustained rise in cytosolic Ca2+ at 2-3 mM extracellular Ca2+. These data provide further evidence for a key role for cell surface carbohydrate-containing moieties in the mechanism through which parathyroid cells "sense" Ca2+ and, in turn, regulate PTH release, phosphoinositide turnover, and the release of intracellular Ca2+ stores. It is possible that the putative Ca2+ receptor is a glycoprotein or is closely associated with glycoproteins or other moieties containing alpha-methyl-D-glucoside or alpha-methyl-D- mannoside residues.


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J. E. Garrett, I. V. Capuano, L. G. Hammerland, B. C. P. Hung, E. M. Brown, S. C. Hebert, E. F. Nemeth, and F. Fuller
Molecular Cloning and Functional Expression of Human Parathyroid Calcium Receptor cDNAs
J. Biol. Chem., May 26, 1995; 270(21): 12919 - 12925.
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