In healthy hearts, myofilaments become more sensitive to Ca2+ as the myocardium is stretched. This effect is known as length-dependent activation and is an important cellular-level component of the Frank–Starling mechanism. Few studies have measured length-dependent activation in the myocardium from failing human hearts. We investigated whether ischemic and non-ischemic heart failure results in different length-dependent activation responses at physiological temperature (37°C). Myocardial strips from the left ventricular free wall were chemically permeabilized and Ca2+-activated at sarcomere lengths (SLs) of 1.9 and 2.3 µm. Data were acquired from 12 hearts that were explanted from patients receiving cardiac transplants; 6 had ischemic heart failure and 6 had non-ischemic heart failure. Another 6 hearts were obtained from organ donors. Maximal Ca2+-activated force increased at longer SL for all groups. Ca2+ sensitivity increased with SL in samples from donors (P < 0.001) and patients with ischemic heart failure (P = 0.003) but did not change with SL in samples from patients with non-ischemic heart failure. Compared with donors, troponin I phosphorylation decreased in ischemic samples and even more so in non-ischemic samples; cardiac myosin binding protein-C (cMyBP-C) phosphorylation also decreased with heart failure. These findings support the idea that troponin I and cMyBP-C phosphorylation promote length-dependent activation and show that length-dependent activation of contraction is blunted, yet extant, in the myocardium from patients with ischemic heart failure and further reduced in the myocardium from patients with non-ischemic heart failure. Patients who have a non-ischemic disease may exhibit a diminished contractile response to increased ventricular filling.
Sarcomere length affects Ca2+ sensitivity of contraction in ischemic but not non-ischemic myocardium
This work is part of a special issue on Myofilament Function 2022.
- Award Id(s): 19TPA34860008,GRNT25460003
- Award Id(s): 1656450
- Award Id(s): HL149164,TR001988
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Bertrand C.W. Tanner, Peter O. Awinda, Keinan B. Agonias, Seetharamaiah Attili, Cheavar A. Blair, Mindy S. Thompson, Lori A. Walker, Thomas Kampourakis, Kenneth S. Campbell; Sarcomere length affects Ca2+ sensitivity of contraction in ischemic but not non-ischemic myocardium. J Gen Physiol 6 March 2023; 155 (3): e202213200. doi: https://doi.org/10.1085/jgp.202213200
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