AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 2 306-R312, Copyright © 1986 by American Physiological Society
Water and nonelectrolyte permeability in brain synaptosomes isolated from normal and uremic rats
A. S. Verkman and C. L. Fraser
Water and nonelectrolyte permeabilities of synaptosomes isolated from the
brain of normal and uremic rats were measured by stopped-flow light
scattering. Intensity of scattered light (550 nm) increased linearly with
decreasing synaptosome size in the range of normal size to 30% of normal
size. In response to a 250-mM inwardly directed gradient of an impermeant
solute (mannitol or sucrose), there was a 100- to 500-ms time course of
increased light scattering resulting from osmotic water efflux. In response
to an inwardly directed urea gradient, light scattering first increased
(water efflux) and then decreased (urea influx) over a 2- to 10-s time
course. Based on an average synaptosome surface-to-volume ratio of 86,000
cm-1, determined by electron microscopy, the permeability coefficient for
osmotic water transport (Pf) is 4.5 X 10(-3) cm/s and for urea transport
(Purea) is 1.5 X 10(-6) cm/s (23 degrees C); temperature-dependent studies
gave an activation energy for Pf of 18 (greater than 16 degrees C) and 3
kcal/mol (less than 16 degrees C) and for Purea of 9.8 kcal/mol (10-55
degrees C). Osmotic water and urea transport were not inhibited by 2 mM
p-chloromercuribenzene sulfonate, 120 microM phloretin, and 10 microM
phenylurea or by exposure to high-energy radiation (0-10 Mrad). Diffusional
water permeability coefficient is approximately 4 X 10(-4) cm/s based on
the time course of light scattering after mixture of synaptosomes in D2O
buffer with isosmotic H2O buffer. Water and urea transport properties of
synaptosomes isolated from uremic rats were not significantly different
from those of normal rats.(ABSTRACT TRUNCATED AT 250 WORDS)
