title: Stimulation of total CO2 flux by 10% CO2 in rabbit CCD: role of an apical Sch-28080- and Ba-sensitive mechanism.
abstract: These studies examine the effect of ambient PCO2 on net bicarbonate (total CO2) absorption by the in vitro perfused cortical collecting duct (CCD) from K-replete rabbits and the mechanism responsible for this effect. Exposure to 10% CO2 increased net bicarbonate flux (total CO2 flux, JtCO2) by 1.8-fold (P < 0.005), and this effect was inhibited by luminal 10 microM Sch-28080, an H-K-adenosinetriphosphatase (H-K-ATPase) inhibitor. In contrast, exposure to 10% CO2 significantly decreased Rb efflux, and this decrement in Rb efflux was blocked by luminal 2 mM Ba, a K channel blocker. Thus transepithelial tracer Rb flux did not increase upon exposure to 10% CO2 as we have observed in this segment under K-restricted conditions. The observation that 10% CO2 increased net bicarbonate absorption without a change in absorptive Rb flux suggested that 10% CO2 increased apical K recycling. To test this hypothesis, we examined whether luminal Ba inhibited the stimulation of luminal acidification induced by 10% CO2. If apical K exit were necessary for full activation of proton secretion, then inhibiting K exit should indirectly affect the stimulation of JtCO2 by 10% CO2. In fact, the effect of 10% CO2 on JtCO2 in the presence of 2 mM luminal Ba was quantitatively indistinguishable from the effect of 10% CO2 on JtCO2 in the presence of 10 microM luminal Sch-28080.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, College of Medicine, University of Florida, Gainesville.
authors.forename: X
authors.initials: X
authors.lastname: Zhou
authors.forename: C S
authors.initials: CS
authors.lastname: Wingo
mesh_terms: D000042:Absorption; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000378:metabolism* / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005260:Female; D007093:Imidazoles / Q000494:pharmacology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects* / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012413:Rubidium / Q000493:pharmacokinetics
chemical_list: D007093:Imidazoles; C035235:Sch 28080; D002245:Carbon Dioxide; D001464:Barium; D012413:Rubidium; D011188:Potassium