Na+-HCO3−cotransporter and intracellular pH regulation in chicken enterocytes

✍ Scribed by M. J. Peral; M. L. Calonge; A. A. Ilundáin

• Book ID: 104749858
• Publisher: Springer
• Year: 1995
• Tongue: English
• Weight: 535 KB
• Volume: 430
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00386154

✦ Synopsis

The current studies examine the presence of the Na+-HCO3 -cotransporter in chicken enterocytes and its role in cytosolic pH (pHi) regulation. The pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to monitor pHi. Under resting conditions, pHi was 7.25 in solutions buffered with bis(2-hydroxyethyl)-1-piperazine ethanesulphonic acid (HEPES) and 7.17 in those buffered with HCO3-. Removal of external Na + decreased pHi and readdition of Na + rapidly increased pH~ towards the control values. These Na+-dependent changes were greater in HCO~--than in HEPES-buffered solutions. In HCO~-free solutions the Na+-dependent changes in pHi were prevented by 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) and unaffected by 4,4'-diisothiocyanatostilbene disulphonic acid (Hz-DIDS). In the presence O f HCO~-, the Na+-induced changes in pHi were sensitive to both EIPA and H2-DIDS. In the presence of EIPA, cells partially recovered from a moderate acid load only when both Na + and HCO~ were present. This pHi recovery, which was EIPA resistant, and dependent on Na + and HCO;-, was inhibited by Hz-DIDS and occurred at equal rates in both Ck-containing and C1--free solutions. Kinetic analysis of the rate of HCO~--and Na +dependent pHi recovery from an acid load as a function of the Na + concentration revealed first-order kinetics with a Michaelis constant, Kin, of 11 mmol/1 Na +. It is concluded that in HCO3-buffered solutions both the Na+/H + exchanger and the Na+-HCO3 -cotransporter participate in setting the resting pHi in isolated chicken enterocytes and help the recovery from acid loads.