Glucose inhibits the high-affinity (Ca2+ + Mg2+)-ATPase in the plasma membrane of a glucose-responsive insulinoma

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Abstract

(Ca2+ + Mg2+)-ATPase enzyme activity of a purified plasma membrane preparation from a glucose responsive rat insulinoma, was characterized as Ca2+-dependent dephosphorylation of [γ-32P]ATP. A high-affinity enzyme with a Km(ATP) raging from 20 to 30 μM and a Km(Ca2+) of 1 μM was identified. Glucose inhibited this high-affinity enzyme in a dose-dependent manner, with no significant inhibition at a concentration between 0 and 5 mM, 50% inhibition at 13.3 mM and 94.5% inhibition at 30 mM. The inhibitory effect of glucose was immediate and rapidly reversible. The effect of stereospecific for the α-anomer. These findings support the concept that glucose acts directly at the β-cell plasma membrane and is involved in the maintenance of elevated intracellular free calcium concentrations associated with insulin release by directly or indirectly inhibiting energy-dependent calcium efflux. Glyceraldehyde (20 mM) increased enzyme activity 3-fold, while other metabolic fuels had no effect. This suggests that inhibition of the enzyme is not an obligatory requirement for insulin release. Calmodulin stimulated the enzyme activity in calmodulin-depleted but not in undepleted membranes. Trifluoperazine (30-100 μM) inhibited (Ca1+ + Mg2+)-ATPase in a dose-dependent manner (14-61% activity) and the activity was also inhibited by vanadate (0.1-1.0 mM) and NaCl (150 mM).

Original languageEnglish (US)
Pages (from-to)333-338
Number of pages6
JournalBBA - Biomembranes
Volume1022
Issue number3
DOIs
StatePublished - Mar 16 1990
Externally publishedYes

Keywords

  • (Rat insulinoma)
  • Beta cell
  • Calcium ion transport
  • Glucose
  • Insulin release

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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