Fig. 7. Calcium signals in rat myotubes: effect of 2-APB and U-73122. Fluorescence images of a rat myotube loaded with fluo-3 were obtained as described in Materials and Methods. A region of the cell was selected and fluorescence intensity was quantified using previously described software (Estrada et al., 2000). High K+-containing solution (47 mM) was perfused. Top panel: myotube in control conditions; images were acquired every 232 milliseconds. At least two major components are evident in the fluorescence signal: a fast signal, associated with E-C coupling and a slow one linked to increases in cytoplasmic and nuclear Ca2+. Bottom panel: fluo-3 loaded myotubes pre-incubated for 30 minutes in the presence of 50 µM 2-APB (filled circles) or 20 minutes in the presence of 10 µM U-73122 (open squares) and depolarized in the presence of the drug. Images were acquired every second. Note that in both cases the slow component of the Ca2+ signal was almost completely inhibited.
