Mechanisms of hco3- secretion in the rabbit connecting segment.
Tsuruoka, Shuichi, and George J. Schwartz.
Department of Pediatrics, University of Rochester School of
Medicine, Rochester, NY 14642
APStracts 6:0109F, 1999.
The CNT contains ( H+ -secreting) and (HCO3--secreting) intercalated
cells and is therefore likely to contribute to acid-base homeostasis.
To characterize the mechanisms of HCO3- transport in the rabbit CNT,
in which there is little definitive data presently available, we
microdissected the segments from the superficial cortical labyrinth,
perfused them in vitro, measured net HCO3- transport (JHCO3) by
microcalorimetry, and examined the effects of several experimental
maneuvers. Mean[angstrom]aSE basal JHCO3 was -3.4[angstrom]a0.1
pmol/min/mm (net HCO3- secretion) and transepithelial voltage was
-13[angstrom]a1 mV (n=47). Net HCO3- secretion was markedly inhibited
by removal of luminal Cl- or application of basolateral H+-ATPase
inhibitors (bafilomycin or concanamycin), maneuvers that inhibit
-intercalated cell function. Net HCO3- secretion was not affected by
inhibitors of -intercalated cell function (basolateral Cl- removal,
basolateral DIDS, or luminal H+-ATPase inhibitors). Net HCO3-
secretion was stimulated by isoproterenol and inhibited by
acetazolamide. These data indicate that 1) CNTs secrete HCO3- via an
apical DIDS-insensitive Cl-/HCO3- exchanger, mediated by a
basolateral bafilomycin- and concanamycin-sensitive H+-ATPase; 2)
inhibition of cytosolic carbonic anhydrase decreases HCO3- secretion;
and 3) stimulation of -adrenergic receptors increases HCO3-
secretion. The failure to influence net HCO3- transport by inhibiting
-IC apical H+-ATPases or basolateral Cl-/HCO3- exchange suggests that
the CNT has fewer functioning -ICs than the CCD. These are the first
studies to examine the rate and mechanisms of HCO3- secretion by the
rabbit CNT; this is clearly an important segment in mediating acid
-base homeostasis.
Received 12 February 1999; accepted in final form 26 May 1999.
APS Manuscript Number F035-9.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 14 June 1999