title: Heterogeneity of chloride/base exchange in rabbit superficial and juxtamedullary proximal convoluted tubules.
abstract: Active transcellular NaCl transport in the proximal convoluted tubule (PCT) is via apical parallel Na/H and Cl/base exchange. The mechanism of Cl/base exchange remains unclear. The present in vitro microperfusion study examined the mechanism of Cl/base exchange in superficial and juxtamedullary PCT by examining the rate of change in intracellular pH in response to luminal Cl removal. In superficial PCT the rate of Cl/base exchange was 24.0 +/- 2.3 without formate, 36.4 +/- 6.6 with 10 microM formate (P < 0.05), and 43.6 +/- 2.8 pmol.mm-1.min-1 (P < 0.001) with 1 mM luminal formate. Cl/base exchange was inhibited by luminal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) in the presence and absence of formate. In juxtamedullary PCT, Cl/base exchange was 22.2 +/- 3.8 without formate and 25.0 +/- 5.4 pmol.mm-1.min-1 in the presence of 1 mM luminal formate [P = not significant (NS)]. Cl/base exchange was inhibited by luminal DIDS in juxtamedullary PCT. The rates of Cl/base exchange in both superficial and juxtamedullary PCT were not affected by 0.1 mM acetazolamide and 2 mM cyanide and were the same in the presence and absence of HCO3/CO2, consistent with Cl/OH rather than Cl/HCO3 exchange. To examine the effect of formate on PCT transport, tubules were perfused with a high-Cl solution without organics simulating late proximal tubular fluid. In superficial PCT net volume absorption (JV) was 0.00 +/- 0.05 in the absence of formate and 0.14 +/- 0.06 nl.mm-1.min-1 in the presence of 1 mM formate (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063, USA.
authors.forename: J N
authors.initials: JN
authors.lastname: Sheu
authors.forename: R
authors.initials: R
authors.lastname: Quigley
authors.forename: M
authors.initials: M
authors.lastname: Baum
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D027963:Chloride-Bicarbonate Antiporters; D003486:Cyanides / Q000494:pharmacology; D005561:Formates / Q000494:pharmacology; D007679:Kidney Medulla; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D011817:Rabbits; D012965:Sodium Chloride / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D017920:Antiporters; D027963:Chloride-Bicarbonate Antiporters; D003486:Cyanides; D005561:Formates; C093920:chloride-base exchanger; C030544:formic acid; D012965:Sodium Chloride; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid