HCO3(-)-dependent ion transport systems and intracellular pH regulation in colonocytes from the chick.
The current study examines the presence of the Na+/HCO3- cotransporter and of the Cl-/HCO3- exchanger in chicken colonocytes and their role in cytosolic pH (pHi) homeostasis. pHi was measured with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) at 25 degreesC. Basal pHi was 7.16 in HEPES-buffered solutions and 7.06 in those buffered with HCO3-. Removal of external Cl- increased pHi and Cl- reinstatement brought the pHi towards resting values. These Cl--induced pHi changes were Na+-independent, inhibited by H2-DIDS and faster in the presence than in the absence of HCO3-. Cells recovered from alkaline loads by a mechanism that was Cl--dependent, Na+-independent and inhibited by H2-DIDS. This rate of Cl--dependent cell acidification decreased as the pHi decreased, with a Hill coefficient value close to 4. Removal of external Na+ decreased pHi and readdition of Na+ brought pHi towards the control values. The rate of the Na+-induced changes was not modified by the presence of HCO3- and was prevented by EIPA and unaffected by H2-DIDS. In the presence of EIPA cells partially recovered from a moderate acid load only when both Na+ and HCO3- were present. The EIPA resistant Na+- and bicarbonate-dependent pHi recovery was inhibited by H2-DIDS and occurred at equal rates in both Cl--containing and Cl--free solutions. It is concluded that in chicken colonocytes bathed in HCO3--buffered solutions, both the Na+/H+ exchanger and the Cl-/HCO3- exchanger participate in setting the resting pHi value. The latter transporter helps the cells to recover from alkaline loads and the first transporter, together with the Na+/HCO3- cotransporter, is involved in pHi recovery from an acid load.
Calonge
M L
ML
Departamento de Fisiología y Biología Animal, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain.
Ilundáin
A A
AA
D000818:Animals; D017920:Antiporters / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D002021:Buffers; D002352:Carrier Proteins / Q000378:metabolism; D002645:Chickens; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007399:Interphase; D007424:Intracellular Fluid / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects; D027982:Sodium-Bicarbonate Symporters
D017920:Antiporters; D001639:Bicarbonates; D002021:Buffers; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D027982:Sodium-Bicarbonate Symporters