Figure 1. Effect of Ca²⁺ on RuV infection.

(A) RuV or SFV was pre-bound to Vero cells on ice for 90 min in binding medium. Cells were shifted to 37°C for 20 min in medium containing the indicated concentrations of CaCl₂, and then cultured for 48 h at 37°C in growth medium plus 20 mM NH₄Cl to prevent secondary infection. Infected cells were scored by immunofluorescence. Infectivity was normalized to that observed at 2 mM CaCl₂, which was ∼15% infected cells. (B) RuV was prebound to Vero cells as in panel A and incubated at 37°C for 20 min in medium with or without 2 mM CaCl₂ (Uptake). The cells were then incubated for 1 h at 37°C in medium with or without 2 mM CaCl₂, to test if infection could be rescued by the addition of Ca²⁺ (Rescue). The cells were then cultured for 48 h at 37°C in growth medium plus 20 mM NH₄Cl, scored by immunofluorescence, and infectivity normalized to that observed when 2 mM CaCl₂ was present throughout the experiment. Data in A are the mean and range of 2 independent experiments. Data in B are the mean and standard deviation from 3 independent experiments. Statistical analysis was performed in (B) using a paired Student's t test.