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Biophys J, August 2002, p. 849-857, Vol. 83, No. 2
Department of Medicine, University of Colorado Health Sciences Center, Denver Colorado 80262 USA
In response to physiological stimuli, neuroendocrine
cells secrete neurotransmitters through a Ca2+-dependent
fusion of secretory granules with the plasma membrane. We studied
insertion of granules in bovine chromaffin cells using capacitance as a
measure of plasma membrane area and fluorescence of a membrane marker
FM1-43 as a measure of exocytosis. Intracellular dialysis with
[Ca2+] (1.5-100 µM) evoked massive exocytosis that was
sufficient to double plasma membrane area but did not swell cells. In
principle, in the absence of endocytosis, the addition of granule
membrane would be anticipated to produce similar increases in the
capacitance and FM1-43 fluorescence responses. However, when
endocytosis was minimal, the changes in capacitance were markedly
larger than the corresponding changes in FM1-43 fluorescence. Moreover,
the apparent differences between capacitance and FM1-43 fluorescence changes increased with larger exocytic responses, as more granules fused with the plasma membrane. In experiments in which exocytosis was
suppressed, increasing membrane tension by osmotically induced cell
swelling increased FM1-43 fluorescence, suggesting that FM1-43 fluorescence is sensitive to changes in the membrane tension. Thus,
increasing membrane area through exocytosis does not swell chromaffin
cells but may decrease membrane tension.
Biophys J, August 2002, p. 849-857, Vol. 83, No. 2
© 2002 by the Biophysical Society 0006-3495/02/08/849/09 $2.00
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