A DRAMATIC PH-DEPENDENT ALTERATION IN ANP RECEPTOR DENSITY - A NOTE FOR USING CULTURED-CELLS

Culture media tend to become acidic when rapidly growing cells are cul tured under batch conditions using a CO2/HCO3- buffer system. The effe cts of this inherent lowering of pH on cellular makeup of cultured cel ls, which have long been ignored, were examined by monitoring the pH a nd number of the atrial natriuretic peptide (ANP) receptors expressed on the cultured bovine endothelial cells. The Eagle's minimum essentia l medium was adjusted to three different pH values of 7.0, 7.4, and 7. 7 and used for 48-h batch cultures. After this 48-h incubation, the pH values of the media were found to be 7.0, 7.1, and 7.4, respectively. These pH shifts had unexpectedly strong influences on the ANP recepto r levels without affecting the affinity. Cells maintained in the sligh tly higher pH medium had a trace amount of the receptor (<10 sites/cel l), while those in the lower pH environment exhibited a large number o f binding sites (40,000 sites/cell). Similar situations might occur in other cellular components and in other types of cells, and therefore, such possibilities should be kept in mind when cultured cell systems are used.