Ca2+ responses in cytomegalovirus-infected fibroblasts of human origin

Abstract

Cytomegalovirus (CMV) infection of fibroblasts of human origin is associated with a cascade of cellular responses (rounding, "contraction," "relaxation," and enlargement). Since in other systems these cellular responses are regulated by intracellular free Ca2+ activity ([Ca2+]i), we measured intracellular Ca2+ responses to CMV infection. At relatively high multiplicities of infection (m.o.i), an influx of Ca2+ was observed within the first hour after CMV infection (p.i.) at which time it was at its maximum rate. Both the time of occurrence and the magnitude of this Ca2+ influx were dependent on the calculated input m.o.i. In CMV-infected cells, [Ca2+]i rose gradually from 80 nM at 0 hr to 174 nM at 48 hr p.i. (about 2.7 times the [Ca2+]i found in mock-infected cells at this time). At 8 and 12 hr p.i. CMV-infected cells consistently contained a somewhat greater level of 45Ca2+ than mock-infected cells, despite the fact that there was only a small increase in [Ca2+]i between CMV and mock-infected cells in the same period. This observation suggests that there may be significant amounts of Ca2+ taken up into intracellular stores. This Ca2+ in intracellular stores may, at later times after infection, contribute to the increase in [Ca2+]i observed from 12 to 48 hr p.i. Ca2+ influx blockers, such as nifedipine and verapamil, inhibited the rise in [Ca2+]i. The increase in [Ca2+]i in response to CMV infection was shown to be dependent on the m.o.i., require infectious virus, and occur under conditions consistent with the expression of immediate-early CMV genes. The capability of inducing such Ca2+ responses was conserved among three laboratory strains of CMV. The CMV-induced Ca2+ responses may be related not only to the development of CMV cytopathology, but also to the replication of CMV, since in other studies cyclic nucleotide modulators and Ca2+ influx blockers were found to inhibit the replication of CMV.