Figure 2. The effects of different concentrations of caffeine on systolic [Ca2+]i.
A, original records showing the effects of applying the indicated concentrations of caffeine for the periods shown. In this experiment the cells were field stimulated rather than voltage clamped. B, time course of change in the amplitude of the systolic Ca2+ transient (^). The continuous curves are first order exponentials fitted to the data with the indicated rate constants. C, histograms showing the relationship between caffeine concentration and various parameters. a, peak Ca2+ transient amplitude in caffeine divided by control; b, steady-state amplitude in caffeine divided by the amplitude of the smallest transient in the undershoot; c, rate constant of decay of potentiation in caffeine divided by the rate constant of recovery on removal of caffeine. Values are means ±s.e.m. for 9 experiments.