A high concentration of Ca ²⁺ in mitochondria is illustrated by punctate labeling in cells, which is consistent with the location of Ca ²⁺ in the mitochondria following fluorescence staining with Rhod-2 AM (Rhod2-AM) at 6 h p.i.. Inhibition of mitochondrial Ca ²⁺ uptake by ruthenium red (RR) or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) in IMR5 cells infected with poliovirus (PV) is also illustrated following fluorescence staining with Rhod-2 AM at 6 h p.i..