Intracellular potentials in rabbit proximal tubules perfused in vitro

HCO3 concentration was increased from 25 to 40 mM without changing peritubular Pco2, a 45% reduction in HCO-reabsorption was observed. This inhibitory effect of increasing peritubular HCO3 concentration was reversed when peritubular pH was normalized by increasing Pco2. Passive permeability for HCO-was also measured and found to be 1.09±0.17 X 10-7 cm2 s-'. Using this value, the passive flux of HCO-could be calculated. Only a small portion (<23%) of the observed changes in net HCO-reabsorption can be explained by the passive HCO-flux. We conclude that luminal and peritubular HCO3 concentrations alter HCO-reabsorption by changing the active H+ secretion rate. Analysis of these data suggest that both luminal and peritubular pH are major determinants of HCO-reabsorption.

“…ability or basolateral membrane PD). In this regard, interesting to compare the first and fourth Biagi et al (40) have observed recently that peritui Fig. 4.…”

Section: Methodsmentioning

confidence: 89%

Effect of luminal and peritubular HCO3(-) concentrations and PCO2 on HCO3(-) reabsorption in rabbit proximal convoluted tubules perfused in vitro.

Sasaki¹,

Berry²,

Rector³

1982

“…The luminal cell membrane electrogenic proton pump should be affected by the electrical potential across the apical cell membrane, while the basolateral cell membrane Cl-HCO3 exchanger should be insensitive to the voltage across the basolateral cell membrane but sensitive to the relative concentrations of Cl and HCO3 across this membrane. Since elevation of peritubular K concentration to 50 mM in proximal convoluted and proximal straight tubule cells as well as CCT cells results in major depolarization of intracellular voltage (10,11,14), we would expect to observe an effect on net HCO3 absorption if the basolateral cell membrane of the MCD cell also possessed high K conductance. Thus, if elevation of the peritubular K concentration to 50 mM significantly depolarizes the cell, one would expect an increase in proton secretion due to improvement of the electrical gradient against which the proton pump must work.…”

Section: Discussionmentioning

confidence: 99%

Medullary collecting duct acidification. Effects of potassium, HCO3 concentration, and pCO2.

Jacobson¹

1984

Abstract. The medullary collecting duct (MCD) from renal outer medulla possesses significant HCO3 absorptive capacity. In vitro microperfusion studies have shown that HCO3 absorption in this segment is carbonic anhydrase dependent, affected by peritubular and luminal chloride concentrations, is independent of the presence of Na or the presence of Na transport, and is stimulated by mineralocorticoid hormone. The present in vitro microperfusion studies defined regulatory influences on MCD acidification as assessed by acute changes in the extracellular K and HCO3 concentrations and pCO2. These studies showed that acute changes in the peritubular K concentration to either 0 mM K or 50 mM K have no significant effect on HCO3 absorption in MCD. Intracellular voltage recordings showed that elevation of peritubular K concentration from 5 to 50 mM produced only a 2.8 mV depolarization of the basolateral cell membrane of MCD cells. In addition, acute reduction of peritubular K from 5 to 0 mM had no significant effect on intracellular voltage. Studies that were designed to assess the effects of HCO3 concentration and pCO2 on acidification showed that acute reduction of peritubular HCO3 concentration from 25 to 5 mM (pH change from 7.4 to 6.8) increased lumen-positive voltage from 30.2±3.8 to 40.0±4.4 mV, and simultaneously increased net HCO3 absorption from 15.6±1.9 to 22.9±2.9 pmol* mm-*min-'. Elevation of peritubular HCO3 concentration from 25 to 50 mM (pH change from 7.4 to 7.8) significantly decreased lumenpositive voltage from 33.8±2.4 to 26.7± 1.5 mV and simultaneously decreased net HCO3 absorption from 17.9±1.2 to 12.8±1.3 pmol *mm-' *min-'. In addition, acute reduction of peritubular pCO2 from 40 to <14 mmHg (final pH 7.8-7.9) significantly decreased lumenpositive voltage from 31±4.4 to 15.7±1.0 mV. Coincidentally, HCO3 absorption decreased significantly from 11.0±3.7 to 5.3±0.7 pmol * mm' * min-'. We conclude that: (a) alteration of peritubular K concentration from 0 to 50 mM in vitro does not affect HCO3 absorption in the MCD, and that this lack of effect appears to be related to a low basolateral cell membrane K conductance; (b) net HCO3 absorption and the associated lumen-positive voltage can be modulated by in vitro changes in peritubular HCO3 and pCO2 (or pH); and (c) the MCD perfused in vitro appears to be a good model for studying the mechanisms and regulation of distal nephron acidification. IntroductionWe, and more recently others, have demonstrated via in vitro microperfusion studies that the medullary collecting duct (MCD)' from renal outer medulla possesses significant HCO3 absorptive capacity (1-4). Indeed, when the rabbit MCD from inner stripe of outer medulla is perfused and bathed in vitro with symmetrical Ringer's HCO3 solutions, transepithelial

“…In the first protocol, we examined the effect of depolarizing the basolateral membrane on J, and PD. During the experimental period, 2 mM BaC12, a potassium conductance inhibitor (12)(13)(14), was added to the bathing media. In the second protocol, we examined the effect of anthracene-9-CO2H, a presumptive Cl-conductance inhibitor (16)(17)(18), on J, and PD.…”

Section: Methodsmentioning

confidence: 99%

“…protocol the effect of depolarizing the basolateral membrane with Ba"+ on NaCi transport was examined (12)(13)(14)(15). Depolarizing the basolateral membrane would decrease the electrical driving force for conductive Cl-exit and inhibit NaCl transport if Cl-exit were conductive.…”

Section: Introductionmentioning

confidence: 99%

Evidence for neutral transcellular NaCl transport and neutral basolateral chloride exit in the rabbit proximal convoluted tubule.

Baum

Berry

1984

A bstract. The electrical nature of active NaCl transport and the significance of a basolateral membrane chloride conductance were examined in isolated perfused rabbit proximal convoluted tubules (PCT). PCT were perfused with a high chloride solution that simulated late proximal tubular fluid and were bathed in an albumin solution that simulated rabbit serum in the control and recovery periods. The electrical nature of NaCl transport was examined by bathing the tubules in a high chloride albumin solution where there were no anion gradients.Volume reabsorption (J,) during the control and recovery period was 0.56 and 0.51 nl/mm. min, respectively, and 0.45 nl/mm -min when the tubules were bathed in a high chloride bath. The transepithelial potential difference (PD) during the control and recovery periods averaged 2.3 mV, but decreased to 0.0 mV in the absence ofanion gradients, which indicated that NaCl transport is electroneutral. Further evidence that NaCl transport is electroneutral was obtained by examining the effect of addition of 0.01 mM ouabain in PCT perfused and bathed with high chloride solutions. The J, was 0.54 nl/mm * min in the control period and not statistically different from zero after inhibition of active transport. The PD was not different from zero in both periods.Two groups of studies examined the role of basolateral membrane CF-conductance in NaCl transport. First, depolarizing the basolateral membrane with 2 mM bath Ba++ did not significantly affect J, or PD. Second, the effect of the presumptive CF-conductance inhibitor anthracene-9-CO2H was examined. Anthracene-9-CO2H did not significantly affect Jv or PD. In conclusion, these data Receivedforpublication 20 December 1983 and in revisedform 5 March 1984. show that NaCl transport in the PCT is electroneutral and transcellular and provide evidence against a significant role for basolateral membrane chloride conductance in the rabbit PCT.