Authors: Susanne Ullrich Kirsten Berit Abel Sabine Lehr Rainer Greger
Publish Date: 1996/08/01
Volume: 432, Issue: 4, Pages: 630-
Abstract
Membrane voltages Vm of INS1 cells an insulinsecreting cell line were measured mostly using the cellattached mode of the patchclamp method The cellattached configuration allowed the cell to be kept intact Measurement of Vm was possible because seal resistances were very high and because the membrane obviously had a sufficiently high conductance probably via K+ channels Resting Vm was −80 ± 1 mV n = 42 and was mainly determined by sulphonylureasensitive K+ATP channels since tolbutamide depolarized the plasma membrane in a concentrationdependent manner and generated action potentials at 50 and 100 μmol/1 DGlucose tested between 05 and 167 mmol/1 also depolarized the plasma membrane in a concentrationdependent manner and induced action potentials at concentrations higher than 56 mmol/1 Similarly forskolin 5 μmol/1 depolarized the cells and increased the frequency of Ca2+mediated action potentials Insulin secretion was measured from cells growing in culture dishes by radioimmunoassay Glucose doubled secretion in INS1 cells whereas tolbutamide had no significant effect on secretion in the presence of 05 mmol/1 and 167 mmol/1 glucose At 3 mmol/1 glucose tolbutamide increased insulin release slightly Forskolin elevated secretion twofold at a low glucose concentration In contrast when glucose or tolbutamide were added together with forskolin secretion was potentiated five to tenfold These results show that glucose induces membrane activation in INS1 cells Furthermore the potent effect of tolbutamide ie to depolarize the plasma membrane without inducing insulin release leads to the conclusion that effects distal to depolarization are pivotal for secretion in INS1 cells
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