AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 6 1254-R1259, Copyright © 1992 by American Physiological Society
Luminal pH in the amphibian distal tubule: effects of carbonic anhydrase and carbonic anhydrase inhibitors
G. Planelles, F. Discala and T. Anagnostopoulos
Institut National de la Sante et de la Recherche Medicale, Unite 323, Centre Hospitalier Universitaire Necker Enfants-Malades, Paris, France.
To better delineate acid-base transport properties in the distal tubule
(DT) of Necturus in vivo, we 1) studied the effects of peritubular (pt)
isohydric increase of PCO2 and [HCO3-]pt on luminal pH (pHlu), and 2)
measured the steady-state pHlu under various experimental conditions. The
experiments were carried out on initial (DTi) or distal (DTd) loops of the
DT in control state and then during intravenous infusion of carbonic
anhydrase (CA) or CA inhibitors (CAI). In control state, isohydric increase
of PCO2 and [HCO3-]pt results in transient acidification of the DTi lumen,
whereas in DTd lumen the same maneuver yields sustained (plateau)
acidification. Under systemic infusion of CAI, isohydric increase of PCO2
and [HCO3-]pt lowers pHlu (sustained fall of pHlu) in DTi and DTd, whereas
under CA infusion both segments exhibit only transient acidification.
During intravenous infusion with benzolamide DTi steady-state pHlu falls,
suggesting that this maneuver inhibits a functional luminal CA, in contrast
to the DTd, whose pHlu remains unaltered. Intravenous infusion of CA
significantly increases steady-state DTd pHlu; by contrast, steady-state
pHlu in DTi does not change. These data are consistent with the presence of
functional luminal CA in the DTi, whereas the DTd segment lacks the luminal
enzyme.
