Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Acetazolamide inhibition of basolateral base exit in rabbit renal proximal tubule S2 segment (1992)
    Springer
    Pflügers Archiv 422 (1992), S. 60-65 
    Details
    ISSN: 1432-2013
    Keywords: Renal proximal tubule ; S2 segment ; Rheogenic Na+-HCO 3 − cotransport ; Cl−/HCO 3 − exchange ; Carbonic anhydrase inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The influence of the carbonic anhydrase inhibitor acetazolamide (ACZ) was investigated on HCO 3 − transport mechanisms in the basolateral cell membrane of rabbit renal proximal tubule. Experiments were performed on isolated S2 segments using double-barrelled microelectrodes to measure cell membrane potential (V b) and cell pH (pHi) during step changes in bath perfusate ion concentrations. Peritubular application of ACZ (1 mmol/l) reduced the initial V b response to 10∶1 reduction of bath HCO 3 − concentration only slightly, from +53.8±4.2 mV to+49.1±0.3 mV (n=5), but caused an intermittent overshooting repolarization in the secondary V b response. In conjunction with these effects it left the initial pHi response virtually unchanged but induced a secondary slow acidification. These observation indicate that — under the present experimental conditions — ACZ does not block the Na+-HCO 3 − cotransporter but acts via inhibition of cytosolic carbonic anhydrase. This was confirmed by studying the effect of elevated intracellular HCO 3 − concentrations under reduced flux conditions and by comparing the concentration dependence of the V b response with the inhibition kinetics of cytosolic carbonic anhydrase. In contrast, peritubular ACZ inhibited Na+-independent Cl−/HCO 3 − exchange in the basolateral cell membrane of S2 segments directly in a similar way to that described in the preceding publication for S3 segments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00381514
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Acetazolamide inhibition of basolateral Cl−/HCO 3 − exchange in rabbit renal proximal tubule S3 segment (1992)
    Springer
    Pflügers Archiv 422 (1992), S. 55-59 
    Details
    ISSN: 1432-2013
    Keywords: Renal proximal tubule ; S3 segment ; Cl−/HCO 3 − exchange ; Carbonic anhydrase inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cell pH (pHi) and cell membrane potential (V b) were measured in isolated S3 segments of rabbit renal proximal tubule with double-barrelled microelectrodes to search for a possible effect of the carbonic anhydrase inhibitor, acetazolamide (ACZ), on Cl−/HCO 3 − exchange in the basolateral cell membrane. ACZ was found to retard and reduce the pHi response to bath Cl− removal reversibly with half-maximal inhibition at 0.42 mmol/l and a rather flat concentration dependence (Hill coefficient ≈ 0.36). To determine whether the retardation resulted from inhibition of cytoplasmic carbonic anhydrase, which might have delayed the attainment of HCO 3 − /CO2 equilibrium, we have measured the response of pHi to step changes in PCO2 in the presence and absence of ACZ. ACZ greatly retarded the pHi response to CO2 steps; however, the concentration dependence differed (half-maximal inhibition at 18 μmol/l) and even at maximal ACZ concentrations the response to CO2 steps was more than twice as fast as the response to Cl− replacement. Since, in addition, the ACZ inhibition of Cl−/HCO 3 − exchange could not be overcome by increasing PCO2 we conclude that the ACZ effect on Cl−/HCO 3 − exchange in rabbit proximal tubule S3 segments does not result from inhibition of cytosolic or membrane-bound carbonic anhydrase, but from a direct interaction with the exchanger molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00381513
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The Na+-HCO 3 − cotransporter operates with a coupling ratio of 2 HCO 3 − to 1 Na+ in isolated rabbit renal proximal tubule (1993)
    Springer
    Pflügers Archiv 425 (1993), S. 409-416 
    Details
    ISSN: 1432-2013
    Keywords: Isolated renal proximal tubule ; Na+-HCO3 − cotransport ; Coupling stoichiometry ; Rheogenicity ; Super-Nernst slope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract All the relevant literature reports indicate that net rates of salt and water absorption and cell membrane potentials (V b) are lower, but intracellular Na+ concentration is higher in rabbit renal proximal tubule in vitro than in rat proximal tubule in vivo. Since the different driving forces should influence basolateral Na+-HCO3 − cotransport we have studied the operation of the cotransporter in isolated rabbit renal proximal tubule in vitro with special emphasis on the stoichiometry of flux coupling (q). Using conventional and ion-selective intracellular microelectrodes three series of experiments were performed: (a) we determined the V b response to a 2∶1 reduction of bath HCO3 − or Na+ concentration, (b) we determined initial efflux rates of HCO3 − or Na+ ions in response to a sudden 10∶1 reduction of bath HCO3 − concentration, and (c) we collapsed the tubules and determined electrochemical driving forces of Na+ and HCO3 − across the basolateral cell membrane under conditions approaching zero net flux in the control state in the presence of Ba2+- and in Cl−-free solutions. All measurements concurrently yielded a coupling ratio of approximately two HCO3 − ions to one Na+ ion (q=2). This result contrasts with the ratio q=3, which we have previously observed in similar experiments on rat renal proximal tubule in vivo [Yoshitomi et al. (1985) Pflügers Arch 405:360] and which was also observed on rabbit renal basolateral cell membrane vesicles in vitro [Soleimani et al. (1987) J Clin Invest 79:1276]. This indicates that — depending on the functional state of the cell — the Na+-HCO3 − cotransporter can operate with variable stoichiometry and suggests that it transports either 1 Na+ + 1 HCO3 − + 1 CO3 2− ion [Soleimani and Aronson (1989) J Biol Chem 264:18 302] or 1 Na+ + 2 HCO3 − ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374866
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The chloride/base exchanger in the basolateral cell membrane of rabbit renal proximal tubule S3 segment requires bicarbonate to operate (1990)
    Springer
    Pflügers Archiv 417 (1990), S. 37-41 
    Details
    ISSN: 1432-2013
    Keywords: Rabbit renal proximal tubule ; S3 segment ; Basolateral cell membrane-Cl−/HCO3 − exchange ; Cell buffer capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Isolated microperfused S3 segments of rabbit renal proximal tubule were investigated with pH-sensitive double-barrelled intracellular microelectrodes to determine whether the Cl−/base exchanger, which we have previously identified in the basolateral cell membrane of this segment requires HCO3 − or can also work in CO2/HCO3 − free conditions. Cell pH (pHi) was measured in response to sudden substitution of bath Cl− by gluconate. In control solutions containing 25 mmol/l HCO3 pHi increased initially by 5.0±0.3 × 10−3 unit/s but after perfusion with CO2/HCO3 −-free solutions pHi of the same cells increased only by 1.3±0.2 × 10−3 unit/s in response to Cl− substitution. From measurements of the cellular buffering power it was calculated that the control base flux had fallen drastically from 3.7±0.3 to 0.3±0.1 × 10−12 mols/s·cm tubule length. To test whether the remaining flux might have resulted from metabolic CO2, oxidative metabolism was poisoned with cyanide (5 mmol/l). This abolished the pH change (ΔpHi) in CO2/HCO3 −-free solutions, but did not affect the pH shift in the presence of HCO3 −. The data indicate that basolateral Cl−/base exchange in S3 segment requires HCO3 − to operate. A model in which HCO3 − absorption proceeds in form of OH− and CO2 can be largely excluded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370766
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...