Figure B: Partial, but unspecific, reconstitution of Ca²⁺ influx in the presence of high extracellular Ca²⁺ and ionomycin concentrations.

(a) Fura-2 loaded T cell lines from one SCID patient (P2) and a normal control (Co) were stimulated with 1 mM ionomycin in the presence of low (0.8 mM) or high (10.8 mM) extracellular Ca²⁺. (b) T cells were stimulated with 3mM ionomycin in the presence of 0.8 mM (control) and 0.8, 2.8 or 10.8 mM (patient 2) extracellular Ca²⁺, respectively. Under these conditions, maximally attainable elevations in [Ca²⁺]i in the SCID patients' T cells were transient and reached ~40% of normal peak concentrations. This increase of [Ca²⁺]i in the patients' cells is most likely due to ionomycin-mediated Ca²⁺ transport into the cell which is independent of Ca²⁺ channels as the level of peak influx at 10mM [Ca²⁺]ex corresponds to the ionomycin concentration (1x10-6 M and 3x10-6 M in panel a and b, respectively).