Increased Cytosolic Free Calcium Concentration Following HCMV Infection of Human Embryo Lung Cells

Calcium response and the role of Ca2+ in HCMV infection were investigated using Fura-2/AM as a fluorescent Ca2+ indicator. Infection of human fibroblasts with human cytomegalovirus (HCMV) resulted in a gradual increase in cytosolic free Ca2+ concentration ([Ca2+]i), and this increase was dependent on the amount of infectious virus. The effects of low Ca2+ medium, Ca2+-specific chelator EGTA, a specific Ca2+ channel blocker nifedipine, and an intracellular Ca2+ chelator BAPTA/AM on HCMV-induced increase in [Ca2+]i were examined. Reduced extracellular Ca2+ concentration by treating HCMV-infected cells with either low Ca2+ medium or EGTA resulted in a diminution of the HCMV-induced [Ca2+]i increase at 6 h after virus infection (p.i.). Treatment with nifedipine also reduced [Ca2+]i in HCMV-infected fibroblasts. Reduction of [Ca2+]i by BAPTA/AM suggests the contribution of intracellular Ca2+ as well as extracellular Ca2+ to the HCMV-induced [Ca2+]i increase. Although both extracellular and intracellular Ca2+ source appear to be important in HCMV-induced increase in [Ca2+]i, their relative order of participation during HCMV infection might be different. Data obtaind from differential addition or removal of nifedipine or BAPTA/AM in HCMV-infected cells implicate that extracellular Ca2+ is responsible for the [Ca2+]i increase in the first 3 h (0 to 3 h p.i.) period, while intracellular Ca2+ in the subsequent 3 h period (3 to 6 h p.i.) of HCMV infection. Treatment of cells transfected with plasmid containing HCMV major immediate early (MIE) promoter fused with a reporter gene with Ca2+ ionophore stimulated the expression of HCMV MIE gene.