Figure 1.

Ca²⁺ spark restitution and cellular Ca²⁺ transients after β-adrenergic stimulation

A, line scan and time courses of repetitive Ca²⁺ sparks induced by 50 nm ryanodine. Spark-to-spark delay and the amplitude of the second spark relative to the first were calculated and analysed (see annotations). B, line scan and time course of whole cell Ca²⁺ transient (1 Hz for 25 s) and subsequent caffeine application (10 mm). Ca²⁺ transient decay and fractional release (Fr_rel = A_trans/A_caff) were measured for analyses (see annotations). C, each column shows spark amplitude restitution (top; normalized amplitude of the second spark vs. the delay between sparks) and spark-to-spark delay histogram (bottom) for different conditions: (1) ISO, ryanodine plus isoproterenol (100 nm); (2) CTRL, ryanodine only. Bold lines show fits to the data of exponential recovery curves with indicated time constant and number of spark pairs. Histogram binning is 100 ms; N refers to number of spark pairs in each group. D, Ca²⁺ transient decay and fractional release in (1) ISO (recorded from 25 and 17 cells, respectively) and (2) CTRL (recorded from 20 and 15 cells, respectively) conditions. If not indicated otherwise, P < 0.01.