ADIPOCYTES Vol. 1, No. 2, pp. 131-138, 2005
ISSN 1550-2082 print, Copyright © 2005 by New Century Health Publishers, LLC

INSULIN INDUCES A RAPID INCREASE IN MEMBRANE AREA IN SINGLE RAT ADIPOCYTES
H. H. Chowdhury1, 2, S. Grilc1, 2 and R. Zorec1, 2

1Laboratory of Neuroendocrinology - Molecular Cell Physiology, Institute of Pathophysiology, Medical School,
University of Ljubljana, 1000 Ljubljana, Slovenia; 2Celica Biomedical Sciences Center, Stegne 21, 1000
Ljubljana, Slovenia
 

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ABSTRACT: Adipocytes vary greatly in their size and
large adipocytes are associated with diseased states such
as the metabolic syndrome and type 2 diabetes. However,
the mechanism of adipocyte growth is not entirely clear.
To study this process, we monitored exocytosis and
endocytosis, which contribute to membrane surface area
fluctuations, and therefore influence cell size. Here we
measured single cell membrane area directly by patchclamp
measurements of membrane capacitance (Cm), a
parameter related to membrane area. In particular, we
studied whether insulin affects membrane area dynamics
in single adipocytes, since increased insulin concentration
is associated with a number of physiological and
pathological conditions. Experimental evidence shows
that a 5-minute exposure of cells to insulin increases
resting Cm by 12 ± 4 %. In controls, the change in Cm
was 2 ± 2 %, not different from zero. By using confocal
microscopy to measure membrane FM1-43 fluorescence
intensity to monitor cumulative exocytosis, we show that
the insulin-induced increase in Cm is due to stimulated
exocytosis.
KEY WORDS: Adipose tissue, Cell size, Exocytosis,
Endocytosis, Insulin