Albumin endocytosis is regulated by heterotrimeric gtp-binding
protein gi3[alpha] in opossum kidney cells.
Brunskill, Nigel J, Neil Cockcroft, Stefan Nahorski, and John Walls.
Department of Nephrology, Department of Pre-Clinical Sciences and
Department of Cell Physiology and Pharmacology, Leicester University
Medical School, Leicester, LE1 9HN, United Kingdom
APStracts 3:0082F, 1996.
Proteinuria is an adverse feature in patients with renal disease,
possibly due to toxicity of albumin to proximal tubular cells.
Albumin is re-absorbed from tubular fluid by receptor mediated
endocytosis. The mechanism of regulation of the endocytosis is
unknown. The large quantities of G-proteins in proximal tubular cell
apical membranes suggests that they may have a regulatory role in
endocytosis. [125I]-albumin uptake was measured in opossum kidney
(OK) cells. This is a saturable process with high (KD 24.3 mg/L) and
low (KD 15.9 g/L) affinity components. The endocytic uptake of gold
-albumin into OK cells was confirmed by electron microscopy. [125I]
-albumin endocytosis in OK cells was inhibited by pertussis toxin but
cholera toxin had no effect. Pertussis toxin also inhibited uptake of
[3H]-inulin. OK cells were stably transfected with a cDNA for the G
-protein subunit Gi3[alpha], and transfectants screened by
immunoblotting. Several Gi3[alpha] overexpressing clones were
detected. OK cells overexpressing Gi3[alpha] demonstrate increased
[125I]-albumin uptake, which is abolished by pertussis toxin, in both
a concentration and time dependent manner. These results suggest that
albumin endocytosis in OK cells is regulated by the G-protein
Gi3[alpha].
Received 20 November 1995; accepted in final form 25 April 1996.
APS Manuscript Number F392-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96