Figure 6

IP ₃ R3 silencing does not modify the sensitivity of the Ca²⁺ release process. (A) Typical Ca²⁺ signals induced by ATP (50 nM - 100 μM) in Fura-2-loaded MCF-7 cells 72 h after their transfection with siC (a) or siR3 (b). ATP triggered intracellular Ca²⁺ signals with a concentration threshold of about 100 nM in both cell batches but IP₃R3 silencing was responsible for a change in the shape of the signal. The percentage of responding cells in siC- and siR3-transfected cells is unchanged whatever the concentration of ATP used (c). Results are representative of 8 independent experiments. (B) The magnitude of the signal is compared at various ATP concentrations (100 nM - 100 μM) and at the maximal concentration of ATP used, the magnitude of the signal is significantly decreased by about 20% (P < 0.01). (C) The number of oscillating cells was investigated at ATP concentrations ranging from 100 nM to 5 μM, and at each concentration the percentage of oscillating cells was largely greater in siR3-transfected cells (P < 0.01 or 0.001).