The ryanodine binding sarcoplasmic reticulum calcium release channel in nonfailing and in failing human myocardium

Abstract

The ryanodine-sensitive Ca2+ release channel (RyaCRC) of the sarcoplasmic reticulum plays a key role in the intracellular Ca2+ handling in cardiomyocytes. Altered expression of the RyaCRC has been supposed to contribute to abnormal cellular Ca2+ handling and to myocardial dysfunction in dilated and ischemic cardiomyopathy. In the present study the 3H-ryanodine binding site in human myocardial homogenates was characterized and the density of the RyaCRC (which corresponds to the cardiac ryanodine receptor) was determined in nonfailing and in failing human myocardium. Homogenates were prepared from nonfailing left ventricular myocardium from the hearts of 5 organ donors (NF) and from failing myocardium from 14 explanted hearts of transplant recipients with end-stage heart failure resulting from dilated (DCM, n = 5) or ischemic (ICM, n = 9) cardiomyopathy. Radioligand saturation binding experiments revealed a specific, high-affinity 3H-ryanodine binding site (Kd-values: NF: 0.65 +/- 0.11 nmol/l, DCM: 0.66 +/- 0.09 nmol/l, ICM: 0.88 +/- 0.18 nmol/l; n.s.) in all preparations. Specific 3H-ryanodine binding depended on the free Ca2+ concentration in the assay. It was maximal at 3-100 micro mol/l Ca2+. The binding was inhibited by the RyaCRC antagonists ruthenium red (Ki-value: 0.32 [0.18-0.56] micromol/l, n = 5) and Mg2+ (Ki-value: 2.95 [1.23-7.11] mmol/l, n = 5). The RyaCRC density was 103.5 +/- 11.9 fmol/mg protein in nonfailing myocardium. There was no significant change in the RyaCRC density in dilated or ischemic cardiomyopathy (112.4 +/- 17.1 and 122.7 +/- 13.9 fmol/mg protein) compared to nonfailing control myocardium. In summary, 3H-ryanodine binds specifically and with high-affinity to the RyaCRC in human myocardium. There is no change in the RyaCRC density in failing myocardium of patients with DCM or ICM in comparison to non-failing controls.

Comparison of the organization of t‐tubules, sarcoplasmic reticulum and ryanodine receptors in rat and human ventricular myocardium

“…The amount of RyR labelling per cluster is also down by approximately 30% in human myocytes, 18 which, together with the reduced RyR cluster density, is in reasonable agreement with reduced ryanodine binding to human heart homogenates compared with that of the rat (100 vs 200 fmol ⁄ mg protein, respectively). 32 Taken together, these data could explain a slower rate of rise of the human Ca 2+ transient compared with rat. 33,34…”

Sarcoplasmic Reticulum Proteins in Heart Failure

“…10 Schumacher et al observed no differences in [ 3 H]ryanodine binding between failing and nonfailing hearts. 11 Finally, Sainte Beuve et al observed an increase of RyRs in failing hearts. 12 At the protein level, no change in RyR expression between failing and nonfailing hearts were consistently observed in three different studies.…”