The “Early–Sorting” Endocytic Compartment of Rat... : Hepatology (original) (raw)
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The “Early–Sorting” Endocytic Compartment of Rat Hepatocytes Is Involved in the Intracellular Pathway of Caveolin–1 (Vip–21)
Pol, Albert1,†; Calvo, Maria1,†; Lu, Albert1; Enrich, Carlos Ph.D.*,1
1_Departament de Biologia Cellular, Institut de Investigacions Biomèdiques August Pi i Sunyer, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain_
* Departament de Biologia Cellular, Facultat de Medicina, Universitat de Barcelona, Casanova 143, 08036 Barcelona, Spain. fax: 34–93–4021907; E-mail: [email protected].
† Albert Pol and Maria Calvo contributed equally to this article.
Received: 14 October 1998; Accepted: 5 March 1999
Abstract
The sinusoidal plasma membrane of the hepatocyte is organized into functional and structural microdomains whose origin, maintenance, and functioning are closely related with the endocytic compartment. Three different subcellular fractions, from rat liver, containing caveolin–1, the structural protein of caveolae, were morphologically and biochemically characterized. A caveolae–enriched plasma membrane fraction (CEF), contains large membrane structures surrounding attached internal plasmalemmal vesicles; the receptor–recycling compartment (RRC), contains tubules and vesicles with similar morphology to the internal vesicles observed by electron microscopy in CEF; and finally, caveolin–1 was also detected in early–sorting endosomes (CURL, compartment of uncoupling receptors and ligands). In this study, we show that following an intravenous administration of retinol–binding protein (RBP), there was a redistribution of caveolin–1 from the plasma membrane (CEF) to intracellular endocytic compartments (RRC and early–sorting endosomes). Thus, these results indicate that, in the hepatocyte, caveolae are dynamic structures actively interacting with the endocytic compartment.
© 1999 John Wiley & Sons, Ltd.