Rapid increase in pH set-point of the Na(+)-in-dependent chloride/bicarbonate antiporter in Vero cells exposed to heat shock.

Internal pH (pHi) is in Vero cells regulated mainly by three antiports. Na+/H+ antiport and Na(+)-dependent Cl-/HCO3- antiport increase pHi in acidified cells, and Na(+)-independent Cl-/HCO3- antiport lowers pHi in cells after alkalinization. The activities of the antiporters were altered in cells after exposure to 41-45 degrees C. Under such conditions the Na+/H+ antiport and the Na(+)-dependent Cl-/HCO3- antiport were both stimulated, whereas the Na(+)-independent Cl-/HCO3- antiport was inhibited in such a way that a higher pH value was required to activate it. This alteration was also induced by some other forms of cellular stress, but did most likely not involve stress proteins as protein synthesis was not required. The possibility of regulation by alteration in protein phosphorylation is discussed.