Effect of protein kinase A on calcium sensitivity of force and its sarcomere length dependence in human cardiomyocytes

J. Van Der Velden, J. W. De Jong, V. J. Owen, P. B.J. Burton, G. J.M. Stienen

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Objective: We investigated whether the Frank-Starling mechanism is absent or preserved in end-stage failing human myocardium and if phosphorylation of contractile proteins modulates its magnitude through the sarcomere length-dependence of calcium sensitivity of isometric force development. Methods: The effect of phosphorylation of troponin I and C-protein by the catalytic subunit of protein kinase A (3 μg/ml; 40 min at 20°C) was studied in single Triton-skinned human cardiomyocytes isolated from donor and end-stage failing left ventricular myocardium at sarcomere lengths measured at rest of 1.8, 2.0 and 2.2 μm. Isometric force development was studied at various free-calcium concentrations before and after protein kinase A incubation at 15°C (pH 7.1). Results: Maximal isometric tension at 2.2 μm amounted to 39.6±10.4 and 33.7±3.5 kN/m2 in donor and end-stage failing cardiomyocytes, respectively. The midpoints of the calcium sensitivity curves (pCa50) of donor and end-stage failing hearts differed markedly at all sarcomere lengths (mean ΔpCa50=0.22). A reduction in sarcomere length from 2.2 to 1.8 μm caused reductions in maximum isometric force to 64% and 65% and in pCa50 by 0.10 and 0.08 pCa units in donor and failing cardiomyocytes, respectively. In donor tissue, the effect of protein kinase A treatment was rather small, while in end-stage failing myocardium it was much larger (ΔpCa50=0.24) irrespective of sarcomere length. Conclusions: The data obtained indicate that the Frank-Starling mechanism is preserved in end-stage failing myocardium and suggest that sarcomere length dependence of calcium sensitivity and the effects of phosphorylation of troponin I and C-protein are independent. Copyright (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)487-495
Number of pages9
JournalCardiovascular Research
Volume46
Issue number3
DOIs
Publication statusPublished - 1 Jun 2000

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