Representative traces of sarcomere shortening recorded in CTRL (black) and NP
(red) cardiomyocytes field-stimulated at 0.5 (A), 1 (B) and 2 (C) Hz. Graphs of resting sarcomere length (D), sarcomere fractional shortening (FS) (E), maximal rate of shortening (−dl/dtmax) (F), and maximal rate of re-lengthening (+dl/dtmax) (G). H. Pie charts of the percentages of cardiomyocytes exhibiting spontaneous contractions (SCs, stippled areas) in CTRL (white) and NPC (red) cells after 60 s of conditional training at 0.5 Hz. I. Graph of number of SCs/cardiomyocyte in the 60 s measurement period. *, p <0.01 vs. CTRL.