The effects of high extracellular Ca2+ and Mg2+ concentrations on the levels of inositol 1,3,4,5-tetrakisphosphate in bovine parathyroid cells

D. Hawkins, P. Enyedi, E. Brown

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Abstract

We examined the effects of calcium (Ca2+), magnesium (Mg2+), and fluoride ion (F-) on inositol phosphate accumulation in bovine parathyroid cells prelabeled with [3H] inositol to determine whether these agents might modulate cytosolic Ca2+ through accumulation of intracellular inositol 1,3,4,5-tetrakisphosphate (IP4), which has been postulated to be a mediator of the influx of extracellular Ca2+. Both Ca2+ and Mg2+ produced dose-dependent increases in IP4 in the presence of Li+, with maximal 19- and 4-fold increases with 5.0 mM Ca2+ and 20 mM Mg2+, respectively. A 50% rise in IP4 was evident within 1 min in response to 5.0 mM Ca2+. In the absence of Li+, a 2-fold increase in IP4 was seen with 5.0 mM Ca2+ only after 15 min. Fluoride ion generated a dose-dependent increase in IP4, with a 48% rise at 10 mM F-, presumably by activating phospholipase-C through a guanine nucleotide regulatory (G) protein-dependent process. We conclude that inositol 1,4,5,-trisphosphate generated in response to high extracellular Ca2+ and Mg2+ concentrations can be converted to IP4 in parathyroid cells. The slow kinetics for the increase in IP4 with high Ca2+ in the absence of Li+, however, do not support a role for IP4 in the early phase of the sustained increase in cytosolic Ca2+ produced by high extracellular Ca2+ concentrations.

Original languageEnglish
Pages (from-to)838-844
Number of pages7
JournalEndocrinology
Volume124
Issue number2
Publication statusPublished - 1989

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GTP-Binding Proteins
Ions
Inositol 1,4,5-Trisphosphate
Inositol Phosphates
Type C Phospholipases
Inositol
Fluorides
Calcium
inositol-1,3,4,5-tetrakisphosphate
magnesium fluoride

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

The effects of high extracellular Ca2+ and Mg2+ concentrations on the levels of inositol 1,3,4,5-tetrakisphosphate in bovine parathyroid cells. / Hawkins, D.; Enyedi, P.; Brown, E.

In: Endocrinology, Vol. 124, No. 2, 1989, p. 838-844.

Research output: Contribution to journalArticle

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abstract = "We examined the effects of calcium (Ca2+), magnesium (Mg2+), and fluoride ion (F-) on inositol phosphate accumulation in bovine parathyroid cells prelabeled with [3H] inositol to determine whether these agents might modulate cytosolic Ca2+ through accumulation of intracellular inositol 1,3,4,5-tetrakisphosphate (IP4), which has been postulated to be a mediator of the influx of extracellular Ca2+. Both Ca2+ and Mg2+ produced dose-dependent increases in IP4 in the presence of Li+, with maximal 19- and 4-fold increases with 5.0 mM Ca2+ and 20 mM Mg2+, respectively. A 50{\%} rise in IP4 was evident within 1 min in response to 5.0 mM Ca2+. In the absence of Li+, a 2-fold increase in IP4 was seen with 5.0 mM Ca2+ only after 15 min. Fluoride ion generated a dose-dependent increase in IP4, with a 48{\%} rise at 10 mM F-, presumably by activating phospholipase-C through a guanine nucleotide regulatory (G) protein-dependent process. We conclude that inositol 1,4,5,-trisphosphate generated in response to high extracellular Ca2+ and Mg2+ concentrations can be converted to IP4 in parathyroid cells. The slow kinetics for the increase in IP4 with high Ca2+ in the absence of Li+, however, do not support a role for IP4 in the early phase of the sustained increase in cytosolic Ca2+ produced by high extracellular Ca2+ concentrations.",
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