Control mechanisms of bicarbonate transport across the rat proximal convoluted tubule

1982 ◽  
Vol 242 (5) ◽  
pp. F532-F543 ◽  
Author(s):  
Y. L. Chan ◽  
B. Biagi ◽  
G. Giebisch
Keyword(s):  
Glass Electrode ◽  
Disulfonic Acid ◽  
Bicarbonate Transport ◽  
Control Mechanisms ◽  
Capillary Perfusion ◽  
Perfusion Rate ◽  
Luminal Perfusion ◽  
Luminal Flow ◽  
Acute Changes ◽  
Convoluted Tubules

Bicarbonate transport (JHCO3) was studied in rat proximal convoluted tubules by luminal and peritubular microperfusion, and the effects on tubular bicarbonate transport of selective changes in luminal and peritubular bicarbonate concentrations and of changes in luminal flow rate were evaluated. A pH glass electrode was used to measure [HCO3(-)] and gave results similar to those of a microcalorimetric method. Increasing the tubular and peritubular [HCO3(-)] at constant luminal perfusion rate (10 nl.min-1) augmented JHCO3, but JHCO3 increased more when pH changes were prevented by PCO2 adjustments (constant peritubular pH) than when pH was allowed to rise with the increase in [HCO3(-)] (constant PCO2). Elevation of the tubular HCO3(-) load by raising [HCO3(-)] stimulated JHCO3 more than when the HCO3(-) load was raised by enhancing luminal perfusion rate at constant [HCO3(-)] An increase in PCO2 at constant peritubular pH increased JHCO3. Diamox and benzolamide inhibited JHCO3 at luminal concentrations of 2-4 X 10(-4) M, yet a small but significant fraction of JHCO3 remained intact. Capillary perfusion with 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (5 X 10(-4) M) depressed JHCO3 by 70%. Acute changes in luminal and peritubular potassium concentrations (range, 2-6 meq/liter) had no effect on JHCO3, but JHCO3 increased moderately but significantly in severe dietary hypokalemia.

Flow dependence of bicarbonate transport in the early (S1) proximal convoluted tubule

1988 ◽  
Vol 254 (6) ◽  
pp. F851-F855 ◽  
Author(s):  
F. Y. Liu ◽  
M. G. Cogan
Keyword(s):  
Wistar Rat ◽  
Proximal Convoluted Tubule ◽  
Bicarbonate Transport ◽  
Bicarbonate Concentration ◽  
Perfusion Rate ◽  
Proton Secretion ◽  
Pump Rate ◽  
Luminal Perfusion ◽  
Luminal Flow

We previously found, using an in vivo microperfusion pump rate of 30 nl/min, that proton secretion in the early (S1) proximal convoluted tubule (PCT) of the Munich-Wistar rat exhibited saturation kinetics. The maximal transport capacity was very high, approximately 500–600 peq.mm-1.min-1. The present studies assessed the change in early PCT acidification kinetics in response to an increase in microperfusion rate to 45 nl/min. First, bicarbonate permeability in the early PCT was measured and was found to be flow dependent. Proton secretion was then calculated using perfusate bicarbonate concentrations from 8 to 100 mM. Saturation of early proximal acidification (Vmax) still occurred at approximately 500–600 peq.mm-1.min-1, but the bicarbonate concentration effecting half-maximal acidification (apparent Km) decreased (from approximately 11 mM at 30 nl/min perfusion rate to less than 6 mM at 45 nl/min). By increasing luminal perfusion rate further to 60 nl/min at constant luminal bicarbonate concentration (25 mM), we confirmed that luminal flow rate did not affect the maximal level of acidification. Similar flow-dependent changes in acidification kinetics in the late PCT were also found, as has been previously shown. In conclusion, although an increase in luminal flow increased bicarbonate permeability and apparent affinity for substrate transport, there was no effect on maximal acidification rate in the early PCT.

Potassium conductance regulation by pH during volume regulation in rabbit proximal convoluted tubules

1992 ◽  
Vol 263 (3) ◽  
pp. F453-F458 ◽  
Author(s):  
J. S. Beck ◽  
S. Breton ◽  
G. Giebisch ◽  
R. Laprade
Keyword(s):  
Intracellular Ph ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Membrane Resistance ◽  
Disulfonic Acid ◽  
Bicarbonate Transport ◽  
Hypotonic Shock ◽  
Reduction Of Co2 ◽  
Convoluted Tubules ◽  
Proximal Convoluted Tubules

When rabbit proximal convoluted tubules were microperfused in the presence of bicarbonate, a 90 mosmol hypotonic shock hyperpolarized the basolateral membrane by 5.5 +/- 1.4 mV, increased basolateral potassium selectivity (tK) from 0.30 +/- 0.02 to 0.45 +/- 0.02, and reduced the basolateral membrane resistance from 4,887 +/- 821 to 2,836 +/- 602 omega.cm. These data show that the hypotonic shock increased absolute basolateral potassium conductance. The same hypotonic shock elevated intracellular pH from 7.18 +/- 0.04 to 7.31 +/- 0.04. When bath pH was increased by 0.2 pH units (by reduction of CO2), intracellular pH rose by 0.13 +/- 0.01. In separate experiments this maneuver hyperpolarized the basolateral membrane by 5.0 +/- 0.8 mV and augmented basolateral tK from 0.58 +/- 0.06 to 0.68 +/- 0.04, suggesting that the basolateral potassium conductance is sensitive to pH changes of a magnitude similar to that evoked by a hypotonic shock. In the nominal absence of bicarbonate or presence of 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) in the bath, the hypotonic shock caused a transient intracellular acidification, suggesting involvement of basolateral bicarbonate transport in the hypotonic shock-induced alkalinization. In the absence of bicarbonate, the hypotonic shock did not increase basolateral tK or induce hyperpolarization of the basolateral membrane. We conclude that the increase in potassium conductance observed during hypotonic shock is at least partly mediated by a bicarbonate-dependent, SITS-sensitive intracellular alkalinization.

Passive driving forces of proximal tubular fluid and bicarbonate transport: gradient dependence of H+ secretion

1983 ◽  
Vol 245 (5) ◽  
pp. F622-F633 ◽  
Author(s):  
Y. L. Chan ◽  
G. Malnic ◽  
G. Giebisch
Keyword(s):  
Driving Forces ◽  
Potential Gradient ◽  
Glass Electrode ◽  
Bicarbonate Transport ◽  
Oncotic Pressure ◽  
Luminal Membrane ◽  
Peritubular Capillaries ◽  
Proximal Tubular ◽  
Luminal Flow ◽  
Pressure Changes

The effect of oncotic pressure changes on fluid (Jv) and net bicarbonate transport (JHCO-3) and the transepithelial bicarbonate permeability (PHCO-3) were measured by an improved luminal and capillary microperfusion method that allows paired experiments on the same tubule. Rat proximal tubules were pump-perfused and Jv and [HCO-3] measured with [14C]inulin and a pH glass electrode. Raising peritubular protein (0-8-15 g/100 ml bovine serum albumin) stimulated Jv and HCO-3 reabsorption. The response to oncotic pressure changes was asymmetrical since changes of the luminal protein concentration had no significant effects. Whereas transepithelial solvent drag effects on HCO-3 must be minimal, peritubular protein most likely stimulates translocation of fluid and bicarbonate from intercellular spaces into peritubular capillaries. PHCO-3 was measured from HCO-3 net flux along a lumen-to-capillary-directed electrochemical potential gradient. In these experiments active H+ transport and Jv were minimized by 10(-4) M acetazolamide and luminal raffinose. PHCO-3 was 1.77 X 10(-5) cm X s-1 and was unaffected by increasing luminal flow rate from 10 to 45 nl X min-1. Since bicarbonate backflux is only a small fraction of physiological rates of JHCO-3, net transport alterations at varying [HCO-3] in the lumen must be due to changes in active HCO-3 (H+) transport. Thus, active H+ ion secretion across the luminal membrane of the proximal tubule is gradient dependent.

Luminal flow rate regulates proximal tubule H-HCO3 transporters

1992 ◽  
Vol 262 (1) ◽  
pp. F47-F54 ◽  
Author(s):  
P. A. Preisig
Keyword(s):  
Proximal Tubule ◽  
Flow Rate ◽  
Initial Rate ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Rate Dependence ◽  
Unstirred Layer ◽  
Disulfonic Acid ◽  
Luminal Flow

In vivo microperfusion was used to examine the mechanism of luminal flow rate dependence of proximal tubule acidification. Luminal flow rate was acutely changed between 5 and 40 nl/min, while luminal and peritubular capillary composition were held constant. With inhibition of basolateral membrane base transport by peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), cell pH (pHi) provides a sensitive index of apical membrane H secretory activity. At a luminal perfusate [HCO3] of 25 mM, progressive increases in luminal flow rate (5----15----25----40 nl/min) caused progressive increases in pHi. This effect was of a smaller magnitude with a luminal perfusate [HCO3] of 60 mM and was further decreased at a luminal perfusate [HCO3] of 100 mM. This pattern of diminished flow rate dependence at higher luminal [HCO3] is consistent with the presence of a luminal unstirred layer, whose composition can be modified by luminal flow rate. The activity of the apical membrane Na-H antiporter, assayed as the initial rate of pHi recovery from an acid load in the presence of peritubular DIDS, was faster at 40 compared with 5 nl/min. Basolateral membrane Na-3HCO3 symporter activity, assayed as the initial rate of pHi recovery from an alkali load in the absence of luminal and peritubular chloride, was faster at 40 compared with 5 nl/min. This effect was eliminated by luminal amiloride, suggesting an indirect effect of flow mediated by changes in pHi secondary to flow rate-dependent changes in apical membrane Na-H antiporter activity. In summary, increases in luminal flow rate directly increase apical membrane H secretion, possibly by modification of a luminal unstirred layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic beta-cell electrical activity: the role of anions and the control of pH

1983 ◽  
Vol 244 (3) ◽  
pp. C188-C197 ◽  
Author(s):  
G. T. Eddlestone ◽  
P. M. Beigelman
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Beta Cell ◽  
Pancreatic Beta Cell ◽  
Proton Exchange ◽  
Disulfonic Acid ◽  
Control Mechanisms ◽  
Exchange System ◽  
Sodium Proton Exchange

The influence of chloride on the mouse pancreatic beta-cell membrane potential and the cell membrane mechanisms controlling intracellular pH (pHi) have been investigated using glass microelectrodes to monitor the membrane potential. It has been shown that chloride is distributed passively across the beta-cell membrane such that chloride potential is equal to the membrane potential. Withdrawal of perifusate chloride or bicarbonate and the application of the drugs 4-acetamido-4'-isethiocyanostilbene-2,2'-disulfonic acid (SITS) and probenecid, both blockers of transmembrane anion movement, have been used to establish that a chloride-bicarbonate exchange system is operative in the cell membrane and that it is one of the control mechanisms of pHi. Amiloride, a specific blocker of the transmembrane sodium proton exchange, has been used to demonstrate that this mechanism is also operative in the beta-cell membrane in the control of pHi. The hypothesis that the calcium-activated potassium permeability is proton sensitive at an intracellular site, a fall in pHi causing a fall in permeability and an increase in pHi causing an increase in permeability, has been used to explain many of the effects observed in this study.

Oxygen delivery to skeletal muscle fibers: effects of microvascular unit structure and control mechanisms

2003 ◽  
Vol 285 (3) ◽  
pp. H955-H963 ◽  
Author(s):  
Arthur Lo ◽  
Andrew J. Fuglevand ◽  
Timothy W. Secomb
Keyword(s):  
Skeletal Muscle ◽  
Muscle Activation ◽  
Tissue Oxygenation ◽  
Oxygen Sensing ◽  
Full Range ◽  
Muscle Fibers ◽  
Motor Units ◽  
Threshold Value ◽  
Control Mechanisms ◽  
Capillary Perfusion

The number of perfused capillaries in skeletal muscle varies with muscle activation. With increasing activation, muscle fibers are recruited as motor units consisting of widely dispersed fibers, whereas capillaries are recruited as groups called microvascular units (MVUs) that supply several adjacent fibers. In this study, a theoretical model was used to examine the consequences of this spatial mismatch between the functional units of muscle activation and capillary perfusion. Diffusive oxygen transport was simulated in cross sections of skeletal muscle, including several MVUs and fibers from several motor units. Four alternative hypothetical mechanisms controlling capillary perfusion were considered. First, all capillaries adjacent to active fibers are perfused. Second, all MVUs containing capillaries adjacent to active fibers are perfused. Third, each MVU is perfused whenever oxygen levels at its feed arteriole fall below a threshold value. Fourth, each MVU is perfused whenever the average oxygen level at its capillaries falls below a threshold value. For each mechanism, the dependence of the fraction of perfused capillaries on the level of muscle activation was predicted. Comparison of the results led to the following conclusions. Control of perfusion by MVUs increases the fraction of perfused capillaries relative to control by individual capillaries. Control by arteriolar oxygen sensing leads to poor control of tissue oxygenation at high levels of muscle activation. Control of MVU perfusion by capillary oxygen sensing permits adequate tissue oxygenation over the full range of activation without resulting in perfusion of all MVUs containing capillaries adjacent to active fibers.

Electrophysiological evidence for Na+-coupled bicarbonate transport in cultured rat hepatocytes

1989 ◽  
Vol 256 (3) ◽  
pp. G491-G500 ◽  
Author(s):  
J. G. Fitz ◽  
M. Persico ◽  
B. F. Scharschmidt
Keyword(s):  
Rat Hepatocytes ◽  
Disulfonic Acid ◽  
Bicarbonate Transport ◽  
Major Pathway ◽  
Voltage Dependent ◽  
Disulfonic Stilbene ◽  
Intracellular Microelectrodes ◽  
Cultured Rat Hepatocytes ◽  
Measure Membrane Potential ◽  
Dependent Mechanism

Recent observations suggest that hepatocytes exhibit basolateral electrogenic Na+-coupled HCO3- transport. In these studies, we have further investigated this transport mechanism in primary culture of rat hepatocytes using intracellular microelectrodes to measure membrane potential difference (PD) and the pH-sensitive fluorochrome 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to measure intracellular pH (pHi). In balanced media containing 25 mM HCO3-, PD averaged -32.1 +/- 0.6 (SE) mV and pHi averaged 7.22 +/- 0.03. PD became more negative (hyperpolarized) when extracellular [HCO3-] was increased and less negative (depolarized) when extracellular HCO3- was decreased. Acute replacement of extracellular Na+ by choline also resulted in membrane depolarization of 18.0 +/- 1.6 mV, suggesting net transfer of negative charge. This decrease in PD upon Na+ removal was HCO3- -dependent, amiloride insensitive, and inhibited by the disulfonic stilbene 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). PD also decreased upon acute exposure to SITS. The degree of depolarization seen with removal of Na+ or HCO3- correlated directly with resting PD (r = 0.81 and 0.95, respectively), suggesting a voltage-dependent mechanism. Removal of extracellular Na+ also decreased pHi to 7.06 +/- 0.02, and this acidification was decreased in the absence of HCO3- or in the presence of SITS or amiloride. These studies provide direct evidence for electrogenic Na+-coupled HCO3- transport in rat hepatocytes. Further, they suggest that it represents a major pathway for conductive movement of Na+ across the membrane and that it contributes, along with Na+-H+ exchange, to the intracellular acidification observed upon removal of extracellular Na+.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of luminal angiotensin II and ANP on early and late cortical distal tubule HCO3- reabsorption

1996 ◽  
Vol 271 (5) ◽  
pp. F977-F984 ◽  
Author(s):  
M. L. Barreto-Chaves ◽  
M. Mello-Aires
Keyword(s):  
Angiotensin Ii ◽  
Exchange Resin ◽  
Distal Tubule ◽  
Ang Ii ◽  
Bafilomycin A1 ◽  
Capillary Perfusion ◽  
At1 Receptors ◽  
Luminal Perfusion

Bicarbonate reabsorption was evaluated by stationary microperfusion “in vivo“ early distal (ED) and late distal (LD) segments of at kidney. Intratubular pH was recorded by double-barreled of H+ exchange resin/reference (1 M KCl) microelectrodes for the determination of HCO3- reabsorption. In the presence of angiotensin II (ANG II) (10(-12) M), a significant increase in HCO3- reabsorption was observed both in ED (from 0.930 +/- 0.060 to 2.64 +/- 0.210 nmol.cm-2.s-1 in luminally perfused tubules and from 0.850 +/- 0.040 to 2.03 +/- 0.210 nmol.cm-2.s-1 during capillary perfusion) and LD segments from 0.310 +/- 0.130 to 2.16 +/- 0.151 nmol.cm-2.s-1 during luminal perfusion and from 0.530 +/- 0.031 to 2.16 +/- 0.211 nmol.cm-2.s-1 with capillary perfusion). The addition of the AT1-receptor antagonist losartan (10(-6) M) to luminal perfusion blocked luminal ANG II-mediated stimulation in ED and LD segments. 5-(N,N-hexamethylene)amiloride (10(-4) M) added to luminal perfusion inhibited luminal ANG II-mediated stimulation in ED (by 81%) and LD (by 54%) segments. The addition of bafilomycin A1 (2 x 10(-7) M) to luminal perfusion does not affect luminal ANG II-mediated stimulation in ED segments but reduces it in LD segments (by 33%). During the addition of atrial natriuretic peptide (ANP) (10(-6) M) or ANG II plus ANP in both segments, no significant differences in HCO3- reabsorption were observed. Our results indicate that luminal ANG II acts to stimulate Na+/H+ exchange in ED and LD segments via activation of AT1 receptors, as well as the vacuolar H(+)-adenosinetriphosphatase in LD segments. ANP does not affect HCO3- reabsorption in either ED or LD segments and does not impair the stimulation caused by ANG II.

scholarly journals Regulatory mechanism underlying cyclic changes in mouse uterine bicarbonate secretion: role of estrogen

Reproduction ◽  
2010 ◽  
Vol 140 (6) ◽  
pp. 903-910 ◽  
Author(s):  
Qiong He ◽  
Hui Chen ◽  
Connie Hau Yan Wong ◽  
Lai Ling Tsang ◽  
Hsiao Chang Chan
Keyword(s):  
Estrous Cycle ◽  
Regulatory Mechanism ◽  
Disulfonic Acid ◽  
Bicarbonate Transport ◽  
Bicarbonate Secretion ◽  
Surface Ph ◽  
Ovariectomized Mice ◽  
Uterine Fluid ◽  
Cyclic Changes

Our previous study has demonstrated that bicarbonate in the uterine fluid plays an indispensable role in sperm capacitation. However, the cellular mechanisms underlying the formation of bicarbonate-rich uterine fluid and the regulatory mechanism remained largely unknown. In this study, the expression profiles of bicarbonate transport/production proteins, the cystic fibrosis transmembrane conductance regulator (CFTR), SLC26A6, carbonic anhydrase 2 (CAR2, CA2) and CAR12 (CA12), throughout the estrous cycle, were examined in the mouse uterus by western blot. The results showed that the maximum expression levels of the proteins examined were observed at estrus. Luminal surface pH measurements showed that the resting uterine surface pH at estrus was significantly higher than that at diestrus, which could be reduced significantly by CFTR blocker, diphenylamine-2,2′-dicarboxylic acid, SLC26A6 inhibitor, 4′,4′-diisothiocyanostilbene-2′,2′-disulfonic acid, and CA inhibitor, acetazolamide. In ovariectomized mice and primary culture of endometrial epithelial cells, estrogen could upregulate CFTR, SLC26A6, CAR2, and CAR12 expression with a corresponding increase in the bicarbonate-dependent short-circuit current (Isc) and endometrial surface pH. The present results have demonstrated dynamic changes in uterine bicarbonate secretion and expression of the proteins involved in bicarbonate secretion during the estrous cycle and suggested a novel role of estrogen in regulating uterine bicarbonate transport, which may be important for successful reproduction.

Bicarbonate transport by isolated perfused rabbit proximal convoluted tubules

1977 ◽  
Vol 233 (4) ◽  
pp. F307-F314 ◽  
Author(s):  
M. Burg ◽  
N. Green
Keyword(s):  
Hydrogen Ion ◽  
Bicarbonate Transport ◽  
Fluid Absorption ◽  
The Mean ◽  
Tubule Cells ◽  
The Relationship ◽  
Convoluted Tubules ◽  
Mean Concentration ◽  
Proximal Convoluted Tubules

Proximal convoluted tubules were dissected from rabbit kidneys and perfused in vitro in order to investigate the relationship between the reabsorption of fluid and of bicarbonate. Bicarbonate was absorbed when it was initially present in the perfusate. At slow rates of perfusion the mean concentration of total CO2 was 9 mM in collected fluid with 25 mM bicarbonate in the bath. At faster rates of perfusion the mean rate of reabsorption was 13.6 pmol cm-1 tubule length s-1. Absorption of bicarbonate was inhibited to a large but not complete extent by elimination of sodium from the perfusate and bath or potassium from the bath, and by addition of ouabain. It was not inhibited by elimination of the organic solutes from the perfusate nor by elimination of chloride from the perfusate and bath. Considered with previous measurements of fluid absorption these results are consistent with the existence of a linked sodium-for-hydrogen ion exchange mechanism at the luminal border of the tubule cells, but there are other possibilities which are discussed. Additionally, the effect of acetazolamide was investigated. The drug virtually completely inhibited bicarbonate absorption and inhibited fluid absorption by 30-40%.

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