RAPID INCREASE IN PH SET-POINT OF THE NA-IN-DEPENDENT CHLORIDE BICARBONATE ANTIPORTER IN VERO CELLS EXPOSED TO HEAT-SHOCK()

Internal pH (pH(i)) is in Vero cells regulated mainly by three antipor ts. Na+/H+ antiport and Na+-dependent Cl-/HCO3- antiport increase pH(i ) in acidified cells, and Na--independent Cl-/HCO3- antiport lowers pH (i) in cells after alkalinization. The activities of the antiporters w ere altered in cells after exposure to 41-45-degrees-C. Under such con ditions the Na+/H+ antiport and the Na+-dependent Cl-/HCO3- antiport w ere both stimulated, whereas the Na+-independent Cl-/HCO3- antiport wa s inhibited in such a way that a higher pH value was required to activ ate it. This alteration was also induced by some other forms of cellul ar stress, but did most likely not involve stress proteins as protein synthesis was not required. The possibility of regulation by alteratio n in protein phosphorylation is discussed.