Figure 7.

Test for Ba²⁺ sequestration by InsP₃-sensitive stores. (control) Cells were preloaded with fura-2 in the presence of 0.4 mM ouabain, washed, and incubated for 1 min in Na-PSS + 1 mM CaCl₂ and then diluted 30-fold into cuvettes containing Li-PSS + 0.3 mM EGTA + 0.3% BSA. BaCl₂ (1 mM), EGTA (10 mM) and ATP (0.3 mM) were added as indicated. (ionomycin) Cells were loaded with fura-2 in the presence of ouabain, washed, and incubated for 1 min in Na-PSS + 0.3 mM EGTA containing 10 μM ionomycin; the cells were then centrifuged and resuspended in Li-PSS + 0.3 mM EGTA + 0.3% BSA. BaCl₂, EGTA, and ATP were added as in the control trace. (Inset) Experimental conditions are as described for the control and ionomycin-treated cells above, except that ATP (0.3 mM) was added as indicated (n = 6).