Islet Studies

Cx36-Mediated Coupling Reduces β-Cell Heterogeneity, Confines the Stimulating Glucose Concentration Range, and Affects Insulin Release Kinetics

  1. Stephan Speier1,
  2. Asllan Gjinovci2,
  3. Anne Charollais2,
  4. Paolo Meda2 and
  5. Marjan Rupnik1
  1. 1Neuroendocrinology, European Neuroscience Institute Göttingen, Göttingen, Germany
  2. 2Department of Cell Physiology and Metabolism, University of Geneva, Genève, Switzerland
  1. Address correspondence and reprint requests to Stephan Speier, The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital L1, Stockholm, Sweden. E-mail: stephan.speier{at}ki.se
Diabetes 2007 Apr; 56(4): 1078-1086. https://doi.org/10.2337/db06-0232

Article Figures & Tables

Figures

  • FIG. 1.
    FIG. 1.

    Residual whole-cell conductance and KATP-channel density of β-cells from NMRI, Cx36+/+, Cx36+/−, and Cx36−/− mice (latter three mice have a C57Bl/6 background). A: Representative traces of current responses to a voltage ramp, after KATP-channel closure by 5 mmol/l intracellular ATP and extracellular application of 100 μmol/l tolbutamide. B: Statistics of the residual conductance measured as the slope of the current response between −100 and −60 mV. C: Maximal KATP-channel conductance after dialysis in the absence of ATP. *P < 0.05, **P < 0.05 vs. value of Cx36+/+ mice.

  • FIG. 2.
    FIG. 2.

    A: Current-voltage relation of Ca2+ channels (n = 11–13) of β-cells from NMRI, Cx36+/+, Cx36+/−, and Cx36−/− mice (latter three on a C57Bl/6 background). B: Representative traces of Ca2+ currents of β-cells from Cx36+/+, Cx36+/−, and Cx36−/− mice in response to a voltage step depolarization to −10 mV from a holding potential of −70 mV. *Significant differences (P < 0.05).

  • FIG. 3.
    FIG. 3.

    K+ currents in coupled and noncoupled β-cells. A: Representative current traces of Cx36+/+ and Cx36−/− β-cells in response to step depolarizations between −50 and +50 mV from a holding potential of −150 mV. B: Current-voltage relationship of peak outward current in β-cells from Cx36+/+, Cx36+/−, and Cx36−/− mice.

  • FIG. 4.
    FIG. 4.

    Excitability of β-cells of Cx36+/+ mice. A: Membrane potential (top trace) and whole-cell conductance (bottom trace) as a result of intracellular dialysis of 5 mmol/l ATP and extracellular application of 100 μmol/l tolbutamide. Gaps in the recording indicate application of voltage protocols to assess channel properties. B: Currents recorded at −50 mV (bottom trace) during electrical activity (top trace).

  • FIG. 5.
    FIG. 5.

    Excitability of β-cells of Cx36+/− mice. A: Membrane potential (top trace) and whole-cell conductance (bottom trace) as a result of intracellular dialysis of 5 mmol/l ATP and extracellular application of 100 μmol/l tolbutamide. B: Currents recorded at −50 mV (bottom trace) during electrical activity (top trace).

  • FIG. 6.
    FIG. 6.

    Excitability of β-cells of Cx36−/− mice. A: Membrane potential (top trace) and whole-cell conductance (bottom trace) as a result of intracellular dialysis of 5 mmol/l ATP and extracellular application of 100 μmol/l tolbutamide. Inset: Closure of KATP channels by dialysis of 5 mmol/l ATP in β-cells of wild-type Cx36+/+ and Cx36−/− mice in two experiments with comparable series resistance. B: Currents recorded at −50 mV (bottom trace) during electrical activity (top trace).

  • FIG. 7.
    FIG. 7.

    Membrane potential changes after dialysis of 5 mmol/l ATP in a β-cell from Cx36+/+ mice, after preincubation of the tissue slice in 13 mmol/l glucose for 7 min.

  • FIG. 8.
    FIG. 8.

    Double patch-clamp experiment on two coupled β-cells within an islet of Langerhans of a Cx36+/+ mouse. Electrical activity was induced by dialysis of both cells with 5 mmol/l ATP and perfusion of the tissue slice with 100 μmol/l tolbutamide. A: Membrane potential recording of one β-cell and its dependence on the membrane potential of the coupled β-cell. The coupled β-cell was clamped to the membrane potentials indicated on top of the graph. B: Average spike amplitude at different clamping voltages. *P < 0.001.

  • FIG. 9.
    FIG. 9.

    Return of high glucose–stimulated insulin release to basal levels in perfused pancreas of wild-type and Cx36-deficient mice. Pancreata of Cx36+/+ (open circles, n = 9) and Cx36+/− mice (gray solid circles, n = 10) showed an exponential decay of insulin output when glucose was switched from 16.4 to 1.4 mmol/l. In contrast, the decay in pancreata of Cx36 (−/−) mice (black solid circles, n = 10) was much more slow. Data are mean ± SE of four to five animals in each group.

Tables

  • TABLE 1

    Spiking characteristics of β-cells from Cx36+/+, Cx36+/−, and Cx36−/− mice

    nMean spiking frequency (Hz)Spike amplitude (mV)
    MeanMaximal
    Cx36+/+85.5 ± 0.817.1 ± 0.824.7 ± 1.3
    Cx36+/−55.2 ± 0.816.0 ± 1.622.0 ± 1.5
    Cx36−/−115.3 ± 0.527.3 ± 1.7*40.9 ± 2.3†

    • Data are mean ± SE.

    • *

      * P < 0.002.

    • †

      † P < 0.001.

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April 2007, 56(4)
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Cx36-Mediated Coupling Reduces β-Cell Heterogeneity, Confines the Stimulating Glucose Concentration Range, and Affects Insulin Release Kinetics
Stephan Speier, Asllan Gjinovci, Anne Charollais, Paolo Meda, Marjan Rupnik
Diabetes Apr 2007, 56 (4) 1078-1086; DOI: 10.2337/db06-0232
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