Figure 1. Store depletion increases [Ca²⁺]_i in mouse PASMCs.

Store depletion increases [Ca²⁺]_i in cultured mouse PASMCs. A, in control experiments, removal of external Ca²⁺ caused a decrease in fluorescence ratio below basal level. Subsequent addition of 2 mm Ca²⁺ caused a very small transient increase in fluorescence ratio, which slowly returned to basal levels (dotted line). B, when applied in Ca²⁺-free solution, depletion of intracellular stores with 10 μm CPA transiently elevated fura-2 fluorescence ratio, indicating Ca²⁺ release from the intracellular stores (arrow). Re-addition of 2 mm Ca²⁺ in the continued presence of CPA caused a transient followed by a sustained increase in fluorescence ratio. The transient but not the sustained component was reduced by 10 μm nifedipine (Nif). C, mean changes in [Ca²⁺]_i compared to the resting [Ca²⁺]_i in control (n= 22) and store depletion (n= 117) experiments. Filled bars indicate mean decrease in [Ca²⁺]_i. Shaded and open bars indicate mean transient and sustained rise in [Ca²⁺]_i, respectively. **P < 0.01 and ⁺⁺P < 0.01, compared to the resting [Ca²⁺]_i (ANOVA). D, bar graph showing the mean changes in transient and sustained rise in [Ca²⁺]_i caused by store depletion after re-addition of 2 mm Ca²⁺, in the absence (n= 117) and presence (n= 296) of 10 μm nifedipine. *P < 0.05 (unpaired t test).