Effects of pauses on Ca2+ transients and SR Ca2+ load. (A) Representative traces of Ca2+ transients from R4496C and WT ventricular myocytes during stimulation pauses imposed after a conditioning stimulation at 3 Hz. Arrows mark the first beats triggered by external stimulation after the resting period. The amplitude of the first peak is analyzed to assess post-rest potentiation of Ca2+-transient amplitude. Diastolic intracellular Ca2+ oscillations and spontaneous Ca2+ transients occur in the R4496C ventricular myocyte during the stimulation pause. (B) Simultaneous Ca2+ fluorescence traces recorded during the application of caffeine at different resting intervals, after a conditioning stimulation at 3 Hz in WT (left) and R4496C (right) myocytes. Traces where caffeine is delivered after pauses of different duration (1.5–3.5 s; conditioning activation train at 3 Hz) are shown superimposed. (C and D) Average percent increase of Ca2+-transient amplitude (C) and SR Ca2+ load (D) after stimulation pauses of different duration in R4496C (n = 22 and 5) versus WT (n = 20 and 4) ventricular myocytes. Error bars represent mean ± SEM.
