Human cytomegalovirus infection stimulates Cl-/HCO3- exchanger activity in human fibroblasts

The effects of human cytomegalovirus (HCMV) infection on Cl-/HCO3- exchanger activity in human lung fibroblasts (MRC-5 cells) were studied using fluorescent, ion-sensitive dyes. The intracellular pH (pH(i)) of mock- and HCMV-infected cells bathed in a solution containing 5% CO2-25 mM HCO3- were nearly the same. However, replacement of external Cl- with gluconate caused an H2DIDS-inhibitable (100 mu M) increase in the pH(i) of HCMV-infected cells but not in mock-infected cells. Continuous exposure to hyperosmotic external media containing CO2/HCO3- caused the pH(i) of both cell types to increase. The pH(i) remained elevated in mock-infected cells. However, in HCMV-infected cells, the pH(i) peaked and then recovered toward control values. This pH(i) recovery phase was completely blocked by 100 mu M H2DIDS. In the presence of CO2/HCO3-, there was an H2DIDS-sensitive component of net Cl- efflux (external Cl- was substituted with gluconate) that was less in mock- than in HCMV-infected cells. When nitrate was substituted for external Cl- (in the nominal absence of CO2/HCO3-), the H2DIDS-sensitive net Cl- efflux was much greater from HCMV- than from mock-infected cells. In mock-infected cells, H2DIDS-sensitive, net Cl- efflux decreased as pH(i) increased, whereas for HCMV-infected cells, efflux increased as pH(i) increased. All these results are consistent with an HCMV-induced enhancement of Cl-/HCO3- exchanger activity.