Glucose-stimulated increase in cytoplasmic pH precedes increase in free Ca2+ in pancreatic beta-cells. A possible role for pyruvate

J Biol Chem. 1994 May 20;269(20):14391-5.

Abstract

The temporal relationship of glucose-induced increases in cytoplasmic pH (pHi) and cytoplasmic free Ca2+ was studied in single mouse pancreatic beta-cells and suspensions of clonal beta-cells (HIT). In both preparations of cells the increase in pHi preceded the cytoplasmic free Ca2+ increase. Therefore the alkalinization cannot be a consequence of the Ca2+ influx. A potential metabolic mechanism for the increase in pHi, involving stimulation of pyruvate transport and oxidation, was demonstrated in a model system of liver mitochondria incubated with pyruvate, ATP, and hexokinase to which glucose was then added to initiate ATP use. The involvement of this mechanism in beta-cells is suggested by the observation that the alkalinization was prevented in most cells by incubation with 3-hydroxycyanocinnamate, a mitochondrial pyruvate transport inhibitor. On the other hand, the inhibited cells exhibited normal Ca2+ responses to glucose stimulation. This indicates that neither pyruvate metabolism nor the alkalinization is of critical importance for the Ca2+ signal, though pyruvate oxidation or its metabolites may be important in downstream regulation of secretion.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Carbon Dioxide / analysis
  • Clone Cells
  • Cytoplasm / drug effects
  • Cytoplasm / metabolism
  • Fluoresceins
  • Fluorescent Dyes
  • Fura-2
  • Glucose / pharmacology*
  • Hydrogen-Ion Concentration*
  • In Vitro Techniques
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism*
  • Kinetics
  • Mice
  • Mice, Obese
  • Models, Biological
  • Pyruvates / metabolism*
  • Spectrometry, Fluorescence
  • Time Factors

Substances

  • Fluoresceins
  • Fluorescent Dyes
  • Pyruvates
  • Carbon Dioxide
  • 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein
  • Glucose
  • Calcium
  • Fura-2