ACTIVE Na+-, Cl-- AND HCO3--DEPENDENT ACID EXTRUSION IN ATLANTIC COD RED BLOOD CELLS IN WINTER ACTIVATED BY HYPERCAPNIA

Abstract

The relationship between intracellular pH (pHi) and extracellular pH (pHe) was investigated in red blood cells from the Atlantic cod (Gadus morhua) in carbon dioxide/bicarbonate-buffered salines. In summer animals (August/September), similar transmembrane distribution ratios of chloride ([Cl-]i/[Cl-]e=rCl-) and protons ([H+]e/[H+]i=rH+) suggested a passive Donnan distribution of these ions across the red blood cell membrane at pHe 6.7­8.4. In winter animals (February/March), a marked discrepancy occurred between rH+ and rCl- at low pHe values. The pronounced increase in rH+ resulted in significantly higher pHi values compared with those of red blood cells from summer animals and at pHe 6.7 pHi exceeded pHe by 0.3 units. The increases in rH+ values were completely abolished by cyanide and 2,4-dinitrophenol. The high disequilibrium rH+ values were sodium-, chloride- and bicarbonate-dependent. During hypercapnic acidosis, proton equivalents were extruded from the red blood cell. The resulting high rH+ values were accompanied by a reduced chloride shift into the red blood cell and a ouabain-insensitive net sodium influx. The net sodium influx into red blood cells from winter animals was significantly reduced in the presence of DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid). The results suggest the activation of a Na+-dependent Cl-/HCO3-exchanger at low pHe in the red blood cells of the Atlantic cod in winter.