title: Rapid insulin-induced exocytosis in white rat adipocytes.
abstract: Insulin is believed to increase glucose permeability of adipocytes by regulating the incorporation of glucose transporters into the plasma membrane by exocytosis. This process involves fusion of membrane-bound cellular compartments with the plasma membrane, thus influencing the plasma membrane area. However, insulin-induced changes in plasma membrane area have not yet been demonstrated. In the present study we monitored fluorescence intensity with a confocal microscope to study the effect of insulin on adipocyte plasma membrane area. After cell isolation and adhesion to a glass cover-slip, adipocytes were stained with the dye FM1-43, a membrane area reporter. At rest, the rate of fluorescence intensity increase was initially high, but gradually stabilized at 2%/min. This steady increase in fluorescence is due to a slow rate of exocytosis coupled to endocytosis, since the removal of FM1-43 from the bath did not abolish FM1-43 fluorescence. Insulin addition caused an abrupt increase of fluorescence intensity of 4%/min, which was significantly higher than in controls. These results suggest rapid, insulin-induced incorporation of new membrane into the plasma membrane by exocytosis.
authors.affiliation: Loboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Medical School, University of Ljubljana, Slovenia. robert.zorec@mf.uni-lj.si
authors.forename: Helena H
authors.initials: HH
authors.lastname: Chowdhury
authors.forename: Marko
authors.initials: M
authors.lastname: Kreft
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
mesh_terms: D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D002478:Cells, Cultured; D005089:Exocytosis / Q000187:drug effects*; D005456:Fluorescent Dyes; D007328:Insulin / Q000494:pharmacology*; D008954:Models, Biological; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: C073804:FM1 43; D005456:Fluorescent Dyes; D007328:Insulin; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds