FIG. 4.

Effects of ehrlichial infection and inhibitors on [Ca²⁺]_i in an individual cell. The rapid and transient increase in [Ca²⁺]_i (as shown by the ratio of emission by fura-2 at 520 nm under stimulation at 340 nm to emission by fura-2 at 520 nm under stimulation at 380 nm) was induced by E. chaffeensis (E.C.) infection in an individual THP-1 cell (A). The increase in [Ca²⁺]_i required active participation of live E. chaffeensis since heat-treated (42 or 60°C, 15 min) E. chaffeensis did not increase the [Ca²⁺]_i. However, the increase in [Ca²⁺]_i induced by ehrlichial infection was prevented by the calcium mobilization inhibitors SKF-96365 and 2-APB (B) or by the PLC inhibitor neomycin and the PTK inhibitor genistein (C). THP-1 cells were loaded with fura-2/AM and treated with or without inhibitors for 1 h before measurements were obtained. Cells were added to poly-l-lysine-coated coverslip chambers, and images (emission at 520 nm after excitation at 340 and 380 nm) were recorded at 1-s intervals for at least 5 min. Host-cell-free E. chaffeensis was added to the chambers after measurements had been obtained for 30 s (vertical arrow). The values are representative of the results of at least three independent experiments, and similar results were obtained for more than 20 cells in each experiment.