In the rabbit small intestine, there are three functionally different brush-border membrane (BBM) anion/HCO3- exchangers: 1) Cl/HCO3- exchange on the BBM of villus cells responsible for coupled NaCl absorption; 2) Cl/HCO3- exchange on the BBM of crypt cells possibly involved in HCO3- secretion; and 3) short-chain fatty acid (SCFA)/HCO3- exchange on the BBM of villus cells, which facilitates SCF...

HCO3- absorption and its association with Na+ absorption has been studied in the rat jejunum in vivo, using a single-pass perfusion technique. The method of disequilibrium pH, the only valid way of demonstrating jejunal H+ secretion, was used to distinguish between an HCO3- pump and H+ secretion as the mechanism of HCO3- absorption. HCO3- stimulated Na+ absorption; Na+ deletion inhibited HCO3 a...

Although endogenous CO2 hydration and serosal HCO3- are both known to contribute to the high rates of intestinal HCO3- secretion important to marine fish osmoregulation, the basolateral step by which transepithelial HCO3- secretion is accomplished has received little attention. Isolated intestine HCO3- secretion rates, transepithelial potential (TEP) and conductance were found to be dependent o...

Membrane transport pathways for transplacental transfer of CO2/HCO3 were investigated by assessing the possible presence of a Cl/HCO3 exchange mechanism in the maternal-facing membrane of human placental epithelial cells. Cl/HCO3 exchange was tested for in preparations of purified brush border membrane vesicles by 36Cl tracer flux measurements and determinations of acridine orange fluorescence ...

In order to clarify the interaction between CO2 diffusion and HCO3- shift in the red blood cell (RBC), HCO3- shift was measured by using a stopped flow method combined with fluorometry. When HCO3- entered the RBC, the intracellular PCO2 increased, causing a secondary outflow of CO2. Conversely, when HCO3- ions flowed out of the RBC, the resulting decrease of PCO2 caused an inward CO2 diffusion....

Pancreatic acini loaded with the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein were used to examine the effect of Ca2(+)-mobilizing agonists on the activity of acid-base transporters in these cells. In the accompanying article (Muallen, S., and Loessberg, P. A. (1990) J. Biol. Chem. 265, 12813-12819) we showed that in 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid (HEPES...

We evaluated the effects of acetazolamide on Na+-HCO3- cotransport in basolateral membrane vesicles isolated from the rabbit renal cortex. Na+ uptake stimulated by an imposed inward HCO3- gradient was not significantly reduced by 1.2 mM acetazolamide, indicating that acetazolamide does not directly inhibit Na+-HCO3- cotransport. 4,4'-Diisothiocyanostilbene-2,2'-disulfonate (DIDS)-sensitive Na+-...

An electrogenic Na+/HCO3- cotransport system was identified and characterized in freshly dissociated salamander Müller (glial) cells. Under voltage-clamp, these cells generated an outward current when external HCO3- concentration [( HCO3-]o) was raised. This current was Na(+)-dependent, Cl(-)-independent, and was blocked by the stilbenes 4,4'-diisothiocyanato-stilbene-2,2'-disulfonate (DIDS) an...

Osmotic-swelling techniques show that HCO3- enters mitochondria by an electrogenic process, effectively HCO3- uniport, under non-energized conditions. This mode of translocation accounts for previous reports of non-entry of HCO3- in experiments with energy-linked Ca2+ uptake. The effects of HCO3- on mitochondrial respiration are reported and discussed.

Marine teleost fish precipitate divalent cations as carbonate deposits in the intestine to minimize the potential for excessive Ca2+ entry and to stimulate water absorption by reducing luminal osmotic pressure. This carbonate deposit formation, therefore, helps maintain osmoregulation in the seawater (SW) environment and requires controlled secretion of HCO3(-) to match the amount of Ca2+ enter...