AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 455-R462, Copyright © 1994 by American Physiological Society
Control of sodium and chloride transport in the thick ascending limb in the avian nephron
E. Osono and H. Nishimura
Department of Physiology and Biophysics, University of Tennessee, Memphis 38163.
We previously reported that birds may concentrate urine by a countercurrent
multiplier mechanism using single-solute (NaCl) recirculation, in which the
thick ascending limb of Henle (TAL) of mammalian-type nephrons provides an
energy source. The Japanese quail TAL has a higher lumen-to-bath Cl flux
(JCl,lb) than that of mammals; the mechanism for maintaining the osmotic
gradient along the medullary cone is unknown. We investigated whether salt
delivery alters the NaCl reabsorption rate in the TAL dissected from both
normal and salt-loaded Japanese quail, Coturnix coturnix, 3-7 wk old. When
salt loading to the TAL was increased by increasing the perfusion flow rate
(PFR), the lumen-to-bath Na and Cl flux coefficients (KNa,lb or KCl,lb,
10(-7) cm2/s) increased, respectively (P < 0.05), from 5.1 +/- 0.9 to
7.6 +/- 0.7 and from 6.8 +/- 0.9 to 8.9 +/- 1.4. Ouabain addition
significantly reduced the KNa,lb. A significant correlation existed between
PFR and JCl,lb (r = 0.69, P < 0.01) and PFR and JNa,lb. When the TAL was
perfused at a low PFR, increasing Cl concentration in the perfusate and
bathing medium from 125 to 175 (P < 0.05) or 225 mM (P < 0.01)
increased JCl,lb but not KCl,lb, while decreasing Cl concentration
decreased JCl,lb but not KCl,lb. Salt loading of intact birds (0.2 M NaCl
drinking water) for 7 days increased the plasma Na level and the cloacal
fluid-to-plasma osmolality ratio from 0.28 +/- 0.07 to 1.06 +/- 0.05 (P
< 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
