Intracellular pH Regulation in Bovine Aortic Endothelial Cells: Evidence of Both Na⁺/H⁺ Exchange and Na⁺-Dependent Cl^–/HCO^–₃ Exchange

Abstract

Regulation of intracellular pH (pH_i) was studied in cultured bovine aortic endothelial cells, an important cell system for cardiovascular research. Suspended cells were acidified by the NH₄Cl prepulse technique as well as by exposure to CO₂/HCO^–₃. Subsequent rates of pH_i recovery were monitored using the fluorescent dye 2′,7′-bis(2-carboxyethyl)-5-(6)-carboxyfluorescein (BCECF). In HCO^–₃-free solutions, an EIPA-sensitive, Na⁺-dependent mechanism fully accounted for realkalinization, namely the Na⁺/H⁺ exchanger (NHE). In the presence of HCO^–₃, an additional acid efflux mechanism was found. This one was dependent on Na⁺ and intracellular Cl^–, EIPA-insensitive but DIDS-sensitive, and therefore represented a Na⁺-dependent Cl^–/HCO^–₃ exchanger (NCBE). In summary, two acid-extruding mechanisms were identified in bovine aortic endothelial cells: NHE and NCBE.

Cloning, Characterization, and Chromosomal Mapping of a Human Electroneutral Na+-driven Cl-HCO3Exchanger

“…1A, but with OH Ϫ replacing HCO 3 Ϫ . In mammalian cells, increases in pH i that appear to depend on Na ϩ , Cl Ϫ , and HCO 3 Ϫ have been described in neurons (14 -16), astrocytes (17,18), renal mesangial cells (19), corneal endothelium (20), bile duct (21), aortic endothelium (22), spermatozoa (23), and various transformed cells (24 -26). However, given the difficulties noted above, definitively ascribing a cell phenotype to a transporter will require molecular tools.…”

Mechanisms of endothelial cell swelling from lactacidosis studied in vitro

“…Swelling in these experiments could be prevented by amiloride analogs, as an indication that a Na ϩ /H ϩ exchanger (NHE) participates in the swelling process. NHEs have been widely studied as membrane mechanisms involved in the regulation of intracellular pH (pH i ) and are present in endothelial cells (4,10). Five NHE isoforms (NHE1-NHE5) represent the major acid-extruding transporters in the absence of bicarbonate (HCO 3 Ϫ ).…”

“…-dependent transporters so far have not been discussed with respect to endothelial swelling, although their participation in the regulation of endothelial pH i is known (1,2,4,10); at physiological pH e , HCO 3 Ϫ -dependent transport systems contribute more to pH i homeostasis than NHE. In most cell types, the contribution of NHE to pH i homeostasis increases with decreasing pH i (4,24).…”

“…In most cell types, the contribution of NHE to pH i homeostasis increases with decreasing pH i (4,24).…”

“…It remains to be determined whether NCBE or Na ϩ -HCO 3 Ϫ cotransport is responsible for HCO 3 Ϫ -dependent swelling, because both are present in endothelium (1,2,4,10). NCBE, however, is less likely to be involved in the swelling response, because uptake of HCO 3 Ϫ by this transporter and the ensuing buffering of protons generates CO 2 , which can readily leave the cell.…”