AJP - Cell Physiology, Vol 264, Issue 1 C40-C47, Copyright © 1993 by American Physiological Society
Brefeldin A inhibits phosphate transport in opossum kidney cells
A. W. Capparelli, M. C. Heng, L. Li, O. D. Jo and N. Yanagawa
Division of Nephrology and Dermatology, Sepulveda Veterans Affairs Medical Center 91343.
Brefeldin A (BFA) is a fungal metabolite that blocks the transport
processes between the endoplasmic reticulum and the Golgi apparatus. In the
present study, we have tested the effect of BFA on phosphate transport in a
kidney epithelial cell line, opossum kidney (OK) cells. Electron microscopy
showed that exposure of OK cells to BFA caused a rapid and reversible
disorganization of Golgi apparatus. Addition of BFA also caused a time (2-8
h)- and dose (1-10 micrograms/ml)-dependent inhibition of Na(+)-dependent
cell phosphate uptake. The inhibition of cell phosphate uptake by BFA was
reversible and was associated with a decrease in the maximum velocity of
phosphate transport. Both the inhibition and the stimulation of cell
phosphate uptake by parathyroid hormone and insulin, respectively, were not
affected by BFA. BFA at 1 microgram/ml concentration did not affect protein
synthesis as determined by [3H]leucine incorporation but diminished the
adaptive increase in cell phosphate uptake in response to 2 or 8 h of
incubation in nominally phosphate-free medium. On the other hand,
inhibition of protein synthesis by cycloheximide (5 microM) abolished the
adaptive increase in cell phosphate uptake in response to 8 but not 2 h of
incubation in nominally phosphate-free medium, indicating the existence of
an early response to phosphate deprivation, which does not require new
protein synthesis but is sensitive to the effect of BFA. In summary,
results of these studies show that, in OK cells, BFA inhibits phosphate
uptake and curtails the adaptive response to phosphate
deprivation.(ABSTRACT TRUNCATED AT 250 WORDS)
