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Title:Acidification of Luminal Fluid by the Rabbit Cortical Collecting Tubule Studied in Vitro
Author(s):Koeppen, Bruce Michael
Department / Program:Physiology and Biophysics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Animal Physiology
Abstract:Studies were done to determine the ability of the rabbit cortical collecting tubule, studied in vitro, to acidify its luminal fluid. The antimony electrode was adapted to allow the continuous measurement of the pH of perfusion fluid as it exitted from the distal end of perfused nephron segments.
Tubular acidification was studied under a variety of conditions. Tubules isolated from rabbits maintained on a standard Purina diet (control) acidified their luminal fluid to pH 5.93 (+OR-) .11 (4.15 to 6.65). The transepithelial voltage (V(,T)('oc)) of control tubules averaged -45.4 (+OR-) 5.5 mV (1umen negative). In most tubules the observed transepithelial gradients for H('+) were in excess of that predicted for simple electrochemical equilibrium of the {H('+)} with the V(,T)('oc), and thus by inference the acidification mechanism appears to be active. Considerable variability of the luminal fluid pH was observed among tubules. This variability could not be attributed to differences in experimental technique, and thus reflected different physiological states of the tubules.
Pretreatment of rabbits with mineralocorticoid (Deoxycorticosterone 5 mg/day for 16-30 days) caused a significant stimulation of both the V(,T)('oc) (-78.7 (+OR-) 8.2 mV) and tubular acidification (pH = 5.43 (+OR-) .16).
Deprivation of food for 1-5 days caused a marked fall in the urine pH from 8.00 (+OR-) .04 to 5.59 (+OR-) .39, with only a slight and not statistically significant fall in luminal fluid pH (5.84 (+OR-) .14).
When studied in the absence of both lumen and bath Na('+) and K('+) the cortical collecting tubule consistently developed a lumen positive V(,T)('oc) (+13.1 (+OR-) 1.9 mV). This lumen positive V(,T)('oc) was partially inhibited when the bath CO(,2) was reduced from 5% (+24.0 (+OR-) 2.7 mV) to 1% (+14.4 (+OR-) 2.8 mV), but not altered when the bath CO(,2) was increased to 10%. Removal of lumen and bath Cl('-) did not significantly alter the magnitude of the V(,T)('oc).
Cortical collecting tubules acidified their luminal fluid in the absence of Na('+) and K('+) generating a luminal fluid pH as low as 5.00 (mean pH = 6.09 (+OR-) .12). Furthermore, acidification under these conditions occurred against a lumen positive voltage.
The effect of several inhibitors on the V(,T)('oc) and luminal fluid pH was also determined. Ouabain (10('-4) M) had no effect on the V(,T)('oc) and luminal fluid pH when added to tubules studied in the absence of Na('+) and K('+). For tubules studied in a Na('+)/K('+) Ringer, ouabain caused the V(,T)('oc) to reverse with a concurrent increase of the luminal fluid pH from 5.85 (+OR-) .10 to 6.27 (+OR-) .07. Acetazolamide (10('-4) M) and SITS (5 x 10('-4) M) inhibited acidification both in the presence and absence of Na('+) transport. Under the latter condition both drugs caused inhibition of both the lumen positive V(,T)('oc) and luminal acidification.
Taken together the results of the present study are consistent with the idea that acidification of the luminal fluid occurs via an active secretory mechanism for H('+) that is independent of Na('+) and K('+) in both the bath and perfusion fluids. The acidification mechanism is not inhibitable by ouabain, but is inhibited by acetazolamide and SITS.
The lumen positive V(,T)('oc) seen in the absence of Na('+) transport is not dependent on Cl('-). On the basis of this, and in view of the parallel changes of the luminal fluid pH with the V(,T)('oc) it seems reasonable to ascribe the lumen positive V(,T)('oc) seen under these conditions to an electrogenic acidification mechanism.
Issue Date:1980
Description:113 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
Other Identifier(s):(UMI)AAI8108566
Date Available in IDEALS:2014-12-14
Date Deposited:1980

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