Effect of luminal angiotensin ii and anp on early and late cortical
distal tubule hco3- reabsorption.
Barreto-Chaves, M. L. M. and M. Mello-Aires.
Department of Physiology and Biophysics, Instituto de
Ci[circumflex]encias Biom[acute]edicas, University of So Paulo, So
Paulo 05508-900, Brazil
APStracts 3:0134F, 1996.
Effect of luminal Angiotensin II and ANP on early and late cortical
distal tubule HCO3- reabsorption. Bicarbonate reabsorption was
evaluated by stationary microperfusion of "in vivo" early
distal (ED) and late distal (LD) segments of rat kidney. Intratubular
pH was recorded by double-barreled H ion-exchange resin/reference (1M
KCl) microelectrodes for the determination of HCO3- reabsorption. In
the presence of ANG II (10-12 M), a significant increase in HCO3-
reabsorption was observed both in ED [from 0.930 ( 0.060 to 2.64 (
0.210 nmol.cm-2.s-1 in luminally perfused tubules and from 0.850 (
0.040 to 2.03 ( 0.210 nmol.cm-2.s-1 during capillary perfusion] and
LD segments [from 0.310 ( 0.130 to 2.16 ( 0.151 nmol.cm-2.s-1 during
luminal perfusion and from 0.530 ( 0.031 to 2.16 ( 0.211 nmol.cm-2.s
-1 with capillary perfusion]. The addition of the AT1-receptor
antagonist Losartan (10-6 M) to luminal perfusion blocked luminal ANG
II-mediated stimulation in ED and LD segments. Hexamethylene
-amiloride (10-4 M) added to luminal perfusion inhibited luminal ANG
II mediated stimulation in ED (by 81%) and LD (by 54%) segments. The
addition of Bafilomycin A1 (2 x 10-7 M) to luminal perfusion does not
affect luminal ANG II mediated stimulation in ED segments but in LD
segments reduces it (by 33%). During the addition of ANP (10-6 M) or
ANG II plus ANP, in both segments, no significant differences in
HCO3- reabsorption were observed. Our results indicate that luminal
ANG II acts stimulating Na+-H+ exchange in ED and LD segments via
activation of AT1 receptors, as well as the vacuolar H+-ATPase in LD
segments. ANP does not affect bicarbonate reabsorption in both ED and
LD segments and does not impair the stimulation caused by ANG II.
Received 19 April 1996; accepted in final form 17 July 1996.
APS Manuscript Number F120-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 August 1996