Water and nonelectrolyte permeability in brain synaptosomes isolated from normal and uremic rats

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)