Stimulation of total CO2 flux by 10% CO2 in rabbit CCD: Role of an apical Sch-28080- and Ba-sensitive mechanism

X. Zhou, C. S. Wingo*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


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 J(tCO2)) by 1.8-fold (P < 0.005), and this effect was inhibited by luminal 10 μM 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 J(tCO2) by 10% CO2. In fact, the effect of 10% CO2 on J(tCO2) in the presence of 2 mM luminal Ba was quantitatively indistinguishable from the effect of 10% CO2 on J(tCO2) in the presence of 10 μM luminal Sch-28080. We interpret these data to suggest that under K-replete conditions 1) acute peritubular acidosis (10% CO2) stimulates luminal acidification by the CCD from normal rabbits via an apical Sch-28080- and Ba-sensitive mechanism that is most consistent with an activation of an H-K-ATPase, 2) the reduction of Rb efflux following exposure to 10% CO2 and the inhibition of this response by 2 mM luminal Ba is compatible with an effect of acidosis on transcellular K conductances plausibly located in principal cells, and 3) the lack of stimulation of Rb efflux by 10% CO2 is in distinct contrast to the effect of this same maneuver to enhance markedly Rb efflux by a Sch-28080-sensitive mechanism in the CCD of K-restricted animals. To explain these observations we propose that renal H-K-ATPase is functionally coupled to an apical Ba-sensitive pathway in the CCD of K-replete rabbits.

Original languageEnglish
Pages (from-to)F114-F120
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Issue number1 36-1
StatePublished - 1994


  • acidification
  • bicarbonate
  • bicarbonate transport
  • cortical collecting duct
  • endocytosis
  • exocytosis
  • potassium
  • potassium absorption
  • potassium channel
  • potassium recycling


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