Figure 6.

CPZ induces transfer of aqueous dye (CF) from RBCs to hemifused NΔ12, Δ12, and GPI-HA–expressing cells. CV-1 cells expressing WT and mutant HAs were prepared as described in the legend to Fig. 4, except that fusion was triggered for 5 min at pH 5.0 and 37°C before reneutralization. After triggering fusion, these cells were exposed to either 0.1 or 0.5 mM CPZ for 1 min at room temperature. The CPZ solution was replaced with PBS⁺ and the cells were observed as above. In control experiments, virtually all WT HA–expressing cells (0.5 μg WT HA, inset graph) were stained with CF in the absence of CPZ. Percent content mixing was determined by dividing the number of cells receiving CF by the number of cells with bound RBCs. Error bars show the SEM for four to five independent experiments (mean ± SEM). Only 0.5 mM CPZ promoted significant content dye transfer between labeled RBCs and cells expressing NΔ12 HA, Δ12 HA, and GPI-HA.