Regulation of fluid-phase endocytosis in alveolar macrophages.
Pataki, Gy, L. Czopf, T. Jilling, N. Marczin, J. Catravas, and S.
Matalon.
Departments of Anesthesiology, Physiology and Biophysics, and
Pediatrics, University of Alabama at Birmingham, Birmingham, Alabama
35233 and Departments of Pharmacology and Toxicology, Medical College
of Georgia, Augusta, Georgia 30912
APStracts 2:0097L, 1995.
We investigated whether fluid-phase endocytosis in rabbit alveolar
macrophages (AM) was regulated by alterations in intracellular cAMP.
Suspensions of freshly isolated AM were incubated with anionic
dextrans (MW=10 kDa), coupled to fluorescein isothiocyanate (FITC
-dextran), at either 37 oC or 4 oC. There was a rapid increase in AM
associated-fluorescence, quantified by laser flow-cytometry and video
microscopy during the first hour of incubation at 37 oC, that was
directly proportional to the amount of tracer present in the medium.
In contrast, at 4 oC, AM fluorescence was similar to
autofluorescence. Incubation of AM with forskolin (50 [mu]M) or IBMX
(0.1 mM) increased their cAMP content by 67 +/- 2 % and 52 +/- 5 %
(mean +/- SEM; n=4) and decreased FITC-dextran uptake by 29 +/- 4 %
and 31 +/- 4 % (mean +/- 1 SEM, n=3). On the other hand, incubation
of AM with 0.5 mM IBMX, inhibited FITC-dextran uptake by 62 +/- 4%
(mean +/- 1 SEM, n=3), without any further increase in cAMP.
Incubation of AM with 0.4 mM CPT-cAMP, a cell-permeable analogue of
cAMP, decreased FITC-dextran uptake 48 +/- 5 % (mean +/- 1 SEM, n=6).
Pulse chase experiments showed that the rate of FITC-dextran
exocytosis was not affected by cAMP. We concluded that fluid-phase
endocytosis in rabbit AM is regulated by cAMP and by an additional,
cAMP-independent mechanism of IBMX.
Received 13 April 1994; accepted in final form 31 May 1995.
APS Manuscript Number L110-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.