4-acetamido-4--isothiocyanatostilbene-2-2--disulfonic-acid and sodium-carbonate

The cation specificity and possible exchange modes of the Na+:CO3(2-):HCO3- cotransporter were evaluated by use of basolateral membrane vesicles isolated from rabbit renal cortex. External Li+ inhibited HCO3- gradient-stimulated 22Na uptake, indicating that Li+ interacts with the Na+:CO3(2-):HCO3- cotransporter. No interaction with K+, choline, Rb+, Cs+, or NH4+ could be similarly detected. Imposing an outward Li+ gradient caused quenching of acridine orange fluorescence in the presence but not in the absence of HCO3-, suggesting that Li+:base cotransport takes place via the Na+:CO3(2-):HCO3- cotransporter. Imposing an outward gradient of unlabeled Na+ stimulated the initial rate of 22Na uptake and induced its transient uphill accumulation, indicating Na(+)-Na+ exchange. Na(+)-Na+ exchange was observed in the presence but not in the absence of HCO3- and was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), suggesting that it occurs via the Na+:CO3(2-):HCO3- cotransporter. Similarly, an outward Li+ gradient stimulated uphill 22Na accumulation, indicating Na(+)-Li+ exchange. Na(+)-Li+ exchange was observed in the presence but not in the absence of HCO3-, and was inhibited by DIDS, suggesting that it also occurs via the Na+:CO3(2-):HCO3- cotransporter. Both Na(+)-Na+ and Li(+)-Na+ exchange modes were sensitive to inhibition by harmaline but not by amiloride. We conclude that Li+ is an alternative substrate for the renal Na+:CO3(2-):HCO3- cotransporter. Transport modes of the system include cation:base cotransport and HCO3-dependent cation-cation exchange.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Amiloride; Animals; Bicarbonates; Biological Transport; Carbonates; Cations; Cell Membrane; Harmaline; Hydrogen-Ion Concentration; In Vitro Techniques; Ionophores; Kidney Cortex; Lithium; Male; Rabbits; Sodium

Intracellular pH (pHi) was measured with proton-sensitive liquid sensor microelectrodes in isolated Necturus antral mucosa, paying special attention to arranging experimental conditions to simulate conditions frequently associated with in vivo "stress ulceration." Intracellular pH in mucosas perfused under standard conditions (Ringer's solution containing HCO3-/CO2) was 7.22 + 0.02 (n = 27). Removal of Na+ and HCO3- or addition of amiloride or 4-acetamido-4-isothiocyanostillbene-2,2-disulfonic acid (blockers of Na+/H+ and Cl-/HCO3-exchangers) had no influence on steady-state pHi, suggesting that these ion exchangers do not significantly contribute to the maintenance of pHi in the presence of normal external pH. Acidification of mucosal (luminal) perfusate to pH 3 (mimicking the presence of gastric acid) had no influence on pHi, but mucosal pH 2 (10 mM HCl) acidified pHi to 6.93 +/- 0.07. Acidification of serosal (nutrient) perfusate to pH 6 (mimicking intramucosal acidosis caused by back-diffusion of luminal H+) acidified pHi to 6.72 +/- 0.10. Removal of Na+ from and addition of amiloride to the serosal perfusate during exposure to serosal pH 6.0 induced further acidification of pHi, suggesting that in this acidotic situation (with very low ambient HCO3- concentration) a Na+/H+ exchanger does contribute to the maintenance of steady-state pHi. Increased PCO2 (10% vol/vol in the gas) in a slightly acidic milieu (mimicking mucosal ischemia) likewise acidified pHi to 6.73 +/- 0.05. A combination of mucosal acid (pH 3), high PCO2 (10% CO2), and low serosal pH (pH 6) (mimicking conditions that prevail, for example, during hemorrhagic shock) acidified pHi and ultimately resulted in cell death. These derangements of intracellular acid-base balance may have pathogenetic importance also in in vivo stress ulceration.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; Amiloride; Animals; Carbonates; Gastric Mucosa; Hydrogen-Ion Concentration; Isotonic Solutions; Membrane Potentials; Microelectrodes; Necturus; Pyloric Antrum; Ringer's Solution; Sodium; Stomach Ulcer; Stress, Physiological

BSC-1 kidney epithelial cells derived from the African green monkey are known to express a Na+HCO3- symport (Jentsch, T. J., Schill, B. S., Schwartz, P., Matthes, H., Keller, S. K., and Wiederholt, M. (1985) J. Biol. Chem. 260, 15554-15560). In the present work, 4,4-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive 22Na+ uptake into confluent monolayers of BSC-1 is measured in the presence of ouabain (10(-4) M) and amiloride (10(-3) M) to define the interactions between Na+ and HCO3- binding and pH. Dependence of DIDS-sensitive 22Na+ fluxes on either Na+ or HCO3- can be described by Michaelis-Menten kinetics. External apparent Km for HCO3- decreases with increasing Na+ concentration (Km app (HCO3-) = 36 +/- 10, 18 +/- 5, and 9 +/- 3 mM at 20, 45, and 151 mM Na+o, respectively (pHo = 7.4)). Similarly, external apparent Km for Na+ decreases with increasing HCO3- concentration (Km app (Na+) = 73 +/- 22, 28 +/- 8, and 14 +/- 4 mM at 6, 17, and 56 mM HCO3o-, respectively (pHo = 7.4)). Vmax app remains constant within the experimental error. When data are replotted as a function of calculated NaCO3- concentration, they can be approximated by a single Michaelis-Menten equation. DIDS-sensitive uptake at constant Na+ and HCO3- displays a broad pH optimum in the range between 7.2 and 7.6. The data are compatible with the ion pair model in which the transported species, NaCO3-, binds to the transport site with Km = 15.3 +/- 4 microM. However, the data may also be fitted by either a random or ordered bireactant system. Sets of parameters necessary for these fits are given.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Bicarbonates; Biological Transport, Active; Carbonates; Carrier Proteins; Cell Line; Chlorocebus aethiops; Epithelium; Hydrogen-Ion Concentration; Kidney; Kinetics; Sodium; Sodium Bicarbonate; Sodium-Bicarbonate Symporters