Extended dynamic range of sarcomere contraction and relaxation if PLN can form pentamers. Measurements of sarcomere length during electrical pacing (0.5 Hz) of cardiomyocytes isolated from TgPLN and TgAFA-PLN hearts. (A) Representative baseline recordings during a cycle of contraction and relaxation; sarcomere kinetics were measured without (BL) and with stimulation with 10⁻⁷ isoproterenol (Iso) for TgPLN (B) and TgAFA-PLN (C); vel contr, velocity of sarcomere contraction; amplitude, change of sarcomere length upon stimulation; vel relax, velocity of sarcomere relaxation. N = 9–16 hearts and 75–123 cells per genotype; unpaired (A) and paired (B, C) two-tailed Students t test.