Figure 4.

Effect of ATP and ATP analogues on intracellular Ca²⁺ concentration ([Ca²⁺]i) in PC12 cells. A. Concentration dependency of [Ca²⁺]i increase elicited by ATP or ATP analogues in NGF-differentiated PC12 cells. Fura-2-loaded PC12 cells were stimulated with the indicated concentrations of ATP (◆), 2-MeSATP (■) or UTP (▲) in HBS, after which the change in [Ca²⁺]i was measured as a fluorescence ratio obtained with excitation at 340 and 380 nm, as described under "Methods." B. Effect of extracellular Ca²⁺ on ATP-induced [Ca²⁺]i increase. Fura-2-loaded PC12 cells were stimulated with the indicated concentrations of ATP in HBS (◆) or in Ca²⁺-free HBS supplemented with 6 mM EGTA (▲). *p < 0.05 compared with HBS. C. Effect of P2 receptor antagonists on ATP-induced [Ca²⁺]i increase. Fura-2-loaded PC12 cells were stimulated with 100 μM ATP in the presence of the indicated concentrations of suramin (◆), PPADS (○) or RB-2 (▲). Data are presented as the mean ± SEM (n = 30–60). *p < 0.05 compared with PPADS or RB-2.