title: Electroneutral K+/HCO3- cotransport in cells of medullary thick ascending limb of rat kidney.
abstract: The renal medullary thick ascending limb (MTAL) of the rat absorbs bicarbonate through luminal H+ secretion and basolateral HCO3- transport into the peritubular space. To characterize HCO3- transport, intracellular pH (pHi) was monitored by use of the pH-sensitive fluorescent probe (2',7')-bis-(carboxyethyl)-(5,6)-carboxyfluorescein in fresh suspensions of rat MTAL tubules. When cells were preincubated in HCO3-/CO2-containing solutions and then abruptly diluted into HCO3-/CO2-free media, the pHi response was an initial alkalinization due to CO2 efflux, followed by an acidification (pHi recovery). The pHi recovery required intracellular HCO3-, was inhibited by 10(-4) M diisothiocyanostilbene-2-2'-disulphonic acid (DIDS), and was not dependent on Cl- or Na+. As assessed by use of the cell membrane potential-sensitive fluorescent probe 3,3'-dipropylthiadicarbocyanine, cell depolarization by abrupt Cl- removal from or addition of 2 mM barium into the external medium did not affect HCO3(-)-dependent pHi recovery, and the latter was not associated per se with any change in potential difference, which indicated that HCO3- transport was electroneutral. The HCO3(-)-dependent pHi recovery was inhibited by raising extracellular potassium concentration and by intracellular potassium depletion. Finally, as measured by use of a K(+)-selective extracellular electrode, a component of K+ efflux out of the cells was HCO3- dependent and DIDS sensitive. The results provide evidence for an electroneutral K+/HCO3- cotransport in rat MTAL cells.
authors.affiliation: Laboratoire de Physiologie et Endocrinologie Cellulaire Rénale, Université Pierre et Marie Curie, Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Leviel
authors.forename: P
authors.initials: P
authors.lastname: Borensztein
authors.forename: P
authors.initials: P
authors.lastname: Houillier
authors.forename: M
authors.initials: M
authors.lastname: Paillard
authors.forename: M
authors.initials: M
authors.lastname: Bichara
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium