Efflux modulation of rhodamine by verapamil is quantified by the RR. RR = the fluorescence intensity of the cellular rhodamine in the presence of verapamil: the fluorescence intensity of the cellular rhodamine content in the absence of verapamil. The RR was measured in RhoD and RhoB CD34⁺ cells and after prestimulation of these cells for 48 hours in vitro with HGFs. The RR of RhoD CD34⁺ cells was significantly higher (P= .009) compared to the RR of RhoB cells. The RR of RhoD CD34⁺ cells was also significantly higher (P = .04) compared to RhoD cells prestimulated with HGFs.