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J. Biol. Chem., Vol. 276, Issue 29, 26762-26768, July 20, 2001
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From the Department of Medicine, University of Colorado Health
Sciences Center, Denver, Colorado 80262
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 ~2%min
Insulin Stimulates Membrane Conductance in a Liver Cell Line
EVIDENCE FOR INSERTION OF ION CHANNELS THROUGH A
PHOSPHOINOSITIDE 3-KINASE-DEPENDENT MECHANISM*
,
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 µM). 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.
*
This work was supported by National Institutes of Health
Grants DK43278 and DK46082 and a grant from the Waterman Foundation (to
J. G. F.) and by American Liver Foundation Grant ALF PN 9801-014 and
a Liver Scholar Award (to R. B. D.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: University of Colorado
Health Sciences Center, Campus Box B158, Rm. 6416, 4200 East 9th Ave.,
Denver, CO 80262. Tel.: 303-315-4010; Fax: 303-315-5711; E-mail:
gordan.kilic@uchsc.edu.
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