FIG. 4.

La³⁺ blocks Ca²⁺ entry induced by rotavirus infection. MA104 and HT29 cell monolayers were trypsinized at 7 h postinfection and loaded with fura-2. The cells were resuspended in 1 ml of medium containing 1 mM Ca²⁺. (A) Effect of La³⁺ on Ca²⁺ entry in rotavirus (a and c)- and mock (b and d)-infected cells. Addition of 100 μM LaCl₃ (c and d) and 5 mM Ca²⁺ (a, b, c, and d) to cell suspensions is indicated by arrows. (B) Dose-response curve for inhibition of Ca²⁺ entry by La³⁺ in rotavirus-infected MA104 cells. La³⁺ concentrations (in micromolar) are indicated at the right of each curve. The inset corresponds to the peak rate of change in [Ca²⁺]_i during the first 15 s following addition of extracellular Ca²⁺ (5 mM) in the presence of different La³⁺ concentrations (d[Ca²⁺]_i/dt_max), calculated as described for Fig. 3. (C) Inhibition of Ca²⁺ entry by La³⁺ in rotavirus-infected HT29 cells. La³⁺ (100 μM) was added at time zero, and 5 mM Ca²⁺ was added to the medium for both untreated and La³⁺-treated infected cells. Results of a representative experiment of a series of three are shown in each case. IC₅₀, 50% inhibitory concentration.