Transport and interaction of nitrogen oxides and NO2 with CO2-HCO3- transporters in pancreatic acini.
Recently, we showed that NO2- increases gap junction (GJ) permeability and synchronizes intracellular Ca2+ concentration oscillations in pancreatic acini (Loessburg et al., J. Biol. Chem. 268: 19769-19775, 1993). NO2- is also an end product of nitric oxide (NO) production and metabolism. Because of the effect of NO2- on GJ permeability and the possible importance of NO2- in NO metabolism and cytotoxicity, we used pancreatic acinar cells and intracellular pH (pHi) measurements to study the interaction of nitrogen oxides and NO2- with cellular proteins. Exposing cells to NO2- resulted in a concentration-dependent cytosolic acidification. The acidification did not require the transport of NO2- and was not mediated by diffusion of HNO2. Because the acidification was prevented by CO2-HCO3- and inhibition of carbonic anhydrase, it is possible that other nitrogen oxides present in a solution containing NO2- enter the cells by diffusion and interact with OH- or H2O to stably acidify the cytosol. NO2- itself is shown to be transported by the HCO3- transporters present in the plasma membrane. Thus manipulation of the cellular Cl- gradient and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) were used to show Cl-/NO2- exchange, whereas stimulation of external Na(+)-dependent amiloride-insensitive and DIDS-sensitive pHi increase in acidified cells was used to demonstrate a Na(+)-(NO2-)n cotransport. Hence NO2- can be a convenient substitute for HCO3- when studying HCO3- transport in an open system. The studies also show that cellular levels of nitrogen oxides and NO2- can be modulated by the cellular HCO3(-)-buffering system.(ABSTRACT TRUNCATED AT 250 WORDS)
Zhao
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Department of Physiology and Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235.
Xu
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Ujiie
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Muallem
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D000143:Acids / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D007474:Ion Exchange; D009569:Nitric Oxide / Q000502:physiology*; D009573:Nitrites / Q000378:metabolism*; D010179:Pancreas / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism
D000143:Acids; D001639:Bicarbonates; D002352:Carrier Proteins; D002712:Chlorides; D009573:Nitrites; D002245:Carbon Dioxide; D009569:Nitric Oxide; D012964:Sodium