Original Paper

Glucose Induces Anion Conductance and Cytosol-To-Membrane Transposition of ICln in INS-1E Rat Insulinoma Cells
M. Jakab¹; M. Grundbichler¹; J. Benicky^2#; A. Ravasio³; S. Chwatal³; S. Schmidt¹; V. Strbak²; J. Fürst³; M. Paulmichl^3,4; M. Ritter¹

¹Institute of Physiology and Pathophysiology, Paracelsus Private Medical University, Salzburg, ²Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, ³Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, ⁴Department of Biomolecular Sciences and Biotechnology, Università degli Studi di Milano, ^#Current address: Section on Pharmacology, National Institute of Mental Health, National Institutes of Health, 9000 Rockville Pike, Bethesda

Cell Physiol Biochem 2006;18:21-34
(DOI: 10.1159/000095131)

  Summary

The metabolic coupling of insulin secretion by pancreatic beta cells is mediated by membrane depolarization due to increased glucose-driven ATP production and closure of K_ATP channels. Alternative pathways may involve the activation of anion channels by cell swelling upon glucose uptake. In INS-1E insulinoma cells superfusion with an isotonic solution containing 20 mM glucose or a 30% hypotonic solution leads to the activation of a chloride conductance with biophysical and pharmacological properties of anion currents activated in many other cell types during regulatory volume decrease (RVD), i.e. outward rectification, inactivation at positive membrane potentials and block by anion channel inhibitors like NPPB, DIDS, 4-hydroxytamoxifen and extracellular ATP. The current is not inhibited by tolbutamide and remains activated for at least 10 min when reducing the extracellular glucose concentration from 20 mM to 5 mM, but inactivates back to control levels when cells are exposed to a 20% hypertonic extracellular solution containing 20 mM glucose. This chloride current can likewise be induced by 20 mM 3-Omethylglucose, which is taken up but not metabolized by the cells, suggesting that cellular sugar uptake is involved in current activation. Fluorescence resonance energy transfer (FRET) experiments show that chloride current activation by 20 mM glucose and glucose-induced cell swelling are accompanied by a significant, transient redistribution of the membrane associated fraction of ICln, a multifunctional ‘connector hub’ protein involved in cell volume regulation and generation of RVD currents.

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