FIGURE 1.

Effect of BaCl₂ on frequency and spatiotemporal pattern of activity. (A) Upper panel depicts the appearance of four partitioned areas that beat independently. Each beat is initiated by an action potential and is associated with Ca-transient (CaT). Presence of Fluo-4 inside the cells results in a brighter field during CaT propagation. No external pacing was used in these experiments. (B) The diagram on the top left depicts the position and shapes of the I- and C-zones. It also shows position of the line used to obtain the x,t scans shown on the right. When a quiescent cell layer is paced (the position of the stimulating electrodes relative to the I-zone used for this figure is shown by a pair of black dots), an x,t scan shows all cells exhibiting CaT along the line at the same time. When barium is applied it shifts pacemaker activity to the I-zone, resulting in a domelike appearance of the x,t signal. The CaT trace on the left illustrates an increased frequency of CaT upon BaCl₂ administration.