Showing papers by "John B. Stokes published in 1989"
TL;DR: Evidence is provided for the operation of a Na-K-Cl cotransport system in rat papillary collecting duct cells that might be involved in active chloride transport in the papillaryCollecting duct and/or volume regulation of the PCD cells.
49 citations
TL;DR: Cet article de synthese fait le point sur le mecanisme de cotransport du chlorure de sodium, le long du tube distal renal, dans l'anse de Henle.
20 citations
TL;DR: The experiments demonstrate that increases in cell [HCO3-] (or perhaps CO2) can stimulate transepithelial anion exchange and suggest that pHi might regulate anion Exchange.
Abstract: In rabbit cortical collecting duct, Cl- self exchange accounts for most of the transepithelial Cl- tracer rate coefficient, KCl (nm/s); a small fraction is effected by Cl--HCO3- exchange and Cl- diffusion. We previously reported that changing from a CO2-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) bath to a 5% CO2-25 mM HCO3- bath stimulates Cl- self exchange. Here, we examine in further detail the individual components of the CO2-HCO3- system that stimulate KCl. Addition of 0.5% CO2 to a HEPES bath (final pH = 7.24) stimulated KCl by 70 +/- 19 nm/s, a delta KCl comparable to that induced by 1% CO2 (pH 7.12), 6% CO2 (pH 6.6), or 6% CO2-25 mM HCO3- (pH 7.4). The roles of intracellular pH (pHi) and HCO3- concentration were examined by clamping pHi using high K+ and nigericin. Increasing pHi from 6.9 to 7.6 in solutions without exogenous CO2 or HCO3- increased KCl by 71 +/- 17 nm/s. These results suggest that pHi might regulate anion exchange. However, during such a pHi-shift experiment, metabolically derived CO2 produces a concomitant change in intracellular HCO3- concentration [( HCO3-]i). To determine whether an increase in [HCO3-]i could stimulate Cl- self exchange, we replaced HEPES with 6% CO2-5 mM HCO3- isohydrically (pHi clamped at 6.9). With this increase in [HCO3-]i at constant pHi, KCl increased by 51 +/- 10 nm/s. These maneuvers had negligible effects on Cl- diffusion and Cl--HCO3- exchange. These experiments demonstrate that increases in cell [HCO3-] (or perhaps CO2) can stimulate transepithelial anion exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
20 citations
TL;DR: It is demonstrated that several Cl- channel blockers can reduce CCD Cl- self exchange when the solutions are buffered in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES).
Abstract: We examined the ability of HCO3- -CO2 to modify the potency of Cl- channel blockers in the renal cortical collecting duct (CCD) for the following two reasons 1) From a practical point of view, there is, to our knowledge, no information regarding the effect of the HCO3- -CO2 buffer system on the potency of Cl- channel blockers 2) We showed in the companion manuscript [Am J Physiol 257 (Cell Physiol 26): C94-C101, 1989] that HCO3- -CO2 stimulates transepithelial anion exchange in the CCD Based on precedent in the literature, we postulated that HCO3- stimulates the basolateral membrane Cl- conductance Here, we demonstrate that several Cl- channel blockers can reduce CCD Cl- self exchange when the solutions are buffered in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) Concentrations of blockers producing 80% inhibition in HEPES, pH 74, produced only 20% inhibition in 25 mM HCO3- -CO2, pH 74 The ability of HCO3- -CO2 to reduce blocker potency had an IC50 of only 2 mM We also examined interactions of HCO3- -CO2 and blockers with regard to the principal cell basolateral Cl- conductance Blockers did not alter the Rb+ flux, a marker of K+ transport, but did reduce transepithelial conductance (GT), ie, the blockers inhibited the principal cell basolateral Cl- conductance As was the case with intercalated cell anion exchange, GT measurements indicated that HCO3- -CO2 impaired the ability of Cl- channel blockers to inhibit the principal cell Cl- conductance(ABSTRACT TRUNCATED AT 250 WORDS)
13 citations
TL;DR: The relationship between Ba2+-induced changes in the K+ and Rb+ permeabilities and in the simultaneously measured GT provides strong evidence that K+ transport across the apical membrane is largely, if not exclusively, conductive.
Abstract: We compared transport of K+ and Rb+ across the rabbit cortical collecting duct to gain insight into the mechanisms of K+ secretion. Passive tracer fluxes, active secretory rates, electrophysiological behavior, and the ability of each ion to support Na+-K+-ATPase activity were determined. When active transport was inhibited by amiloride, K+ permeability was twice the Rb+ permeability. Transepithelial conductance (GT) was half as great in solutions where 5 mM Rb+ replaced 5 mM K+. When 4 mM Ba2+ was added to the lumen, both Rb+ and K+ permeability fell to values not different from that expected for paracellular diffusion. The relationship between Ba2+-induced changes in the K+ and Rb+ permeabilities and in the simultaneously measured GT provides strong evidence that K+ transport across the apical membrane is largely, if not exclusively, conductive. We also determined that net K+ secretion is greater than net Rb+ secretion (when each is the abundant ion). The reasons for this difference probably involve several steps in the K+ secretory process and include the following: 1) reduced ATPase activity in the presence of Rb+ (approximately 80%) compared with K+, 2) reduction of Na+ absorption, and 3) partial blockade of the apical (and perhaps basolateral) K+ conductance. Although there were quantitative differences between K+ and Rb+ transport, we found no evidence suggesting that these ions are transported by different mechanisms.
12 citations