Figure 4.

IP₃ generated by PLCγ is required for ATP-induced arrest of Ca²⁺ spiking. Fluo3 was coinjected in cardiomyocytes with an anti-yes antibody (A), an anti-SH2PLCγ antibody (B and C), a wild-type (wt GSTSH2; D) or mutated (mt GSTSH2; E) glutathione-S-transferase fusion protein, or heparin (F). The effects of ATP (20 μM) or prostaglandin F_2α (PGF_2α; 1 μM in C) on Ca²⁺ oscillations were tested on spontaneously beating cells. [Ca²⁺]_i changes were recorded using a CCD camera and the Argus-50 image processor (Hamamatsu). The horizontal bar below each recording indicates the time scale (1 min). The y-axes of the graphs represent the Fluo3 fluorescence ratio between each image of the series and the first image acquired at resting [Ca²⁺]_i as calculated by the Argus-50 software. Three to four images were acquired per second. The number of experiments performed in each experimental condition is indicated in the text. In this series of experiments, a block in Ca²⁺ oscillations was taken as a readout of the ATP effect because the limited time acquisition of the camera did not allow for an accurate estimation of the spiking rate.