Insulin stimulates membrane conductance in a liver cell line: evidence for insertion of ion channels through a phosphoinositide 3-kinase-dependent mechanism.
Activation of insulin receptors stimulates a rapid increase in the ion permeability of liver cells. To evaluate whether this response involves insertion of ion channels, plasma membrane turnover was measured in a model liver cell line using the fluorescent membrane marker FM1-43. Under basal conditions, the rate of constitutive membrane turnover was approximately 2%min(-1), and balanced exocytosis and endocytosis maintained the total cell membrane area constant. Exposure to insulin stimulated a transient increase in membrane turnover of up to 10-fold above constitutive rates. The response was concentration-dependent (0.001-10 microm). Insulin also caused a parallel increase in membrane conductance as measured by whole-cell patch clamp recording due to opening of Cl(-)- and K(+)-selective ion channels. The insulin-stimulated membrane turnover did not appear to involve the constitutive recycling compartments, suggesting that a distinct pool of vesicles may be involved. The effects of insulin on membrane turnover and membrane conductance were inhibited by blockers of phosphoinositide 3-kinase LY294002 and wortmannin or by disrupting microtubule assembly with nocodazole. Taken together, these findings indicate that insulin stimulates recruitment of new membranes through phosphoinositide 3-kinase-dependent mechanisms. Thus, regulated insertion of a separate population of ion channel-containing vesicles may represent one mechanism for mediating the changes in membrane conductance that are essential for the cellular response to insulin.
Kilic
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G
Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. gordan.kilic@uchsc.edu
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Fitz
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D000818:Animals; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects*; D008870:Microtubules / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured
D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases