AJP - Cell Physiology, Vol 257, Issue 2 C315-C322, Copyright © 1989 by American Physiological Society
High-affinity uptake of 67Cu into a veratridine-releasable pool in brain tissue
A. Barnea, D. E. Hartter and G. Cho
Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235.
We have previously characterized two saturable, ligand-dependent processes
for 67Cu uptake by hypothalamic slices: a high- and low-affinity process
(22). In this study, we wished to ascertain if veratridine, a secretagogue
that mimics a physiological release process, stimulates the release of
newly taken up 67Cu and whether uptake of 67Cu into the releasable pool of
copper is dependent on the process of 67Cu uptake. Hypothalamic or caudate
slices from male rats were loaded for 30 min with 67Cu complexed to
histidine (His) under conditions favoring high- or low-affinity uptake.
First, we assessed the stability of the newly taken up 67Cu and found that,
regardless of the mode of 67Cu entry into the tissue, greater than or equal
to 85% of the 67Cu is retained in tissues incubated for 3 h in 67Cu-free
buffer. Moreover, the 67Cu taken up by the high-affinity process was not
displaced by 15-fold molar excess of nonradiolabeled Cu2+, histidine,
albumin, or Zn2+, and only 20-30% of the 67Cu taken up by the low-affinity
process was displaced by 10-fold excess Cu2+ or albumin. Next, we assessed
veratridine stimulation of 67Cu release and found that 67Cu release
occurred only from tissues loaded with the high- but not with the
low-affinity process. This effect of veratridine was calcium dependent and
was blocked by Tetrodotoxin, a specific blocker of the voltage-sensitive
Na+ channel. In addition, we confirmed our earlier observation that a
depolarizing concentration of K+ stimulates 67Cu release.(ABSTRACT
TRUNCATED AT 250 WORDS)
