Increased expression of isoform 1 of the sarcoplasmic reticulum Ca2+-release channel in failing human heart

Background-The sarcoplasmic reticulum (SR) Ca2+-release channel plays a key role in the excitation-contraction coupling of cardiac myocytes. Because r espective alterations have been reported in human heart failure, we investi gated isoform expression of the SR Ca2+-release channel in human hearts fro m patients with terminal heart failure (dilated cardiomyopathy [DCM], n=8) and nonfailing organ donors (NF, n=8). Methods and Results-Expression of mRNA of SR Ca2+-release channel isoforms in isolated human cardiomyocytes and myocardial tissue was analyzed by reve rse-transcription polymerase chain reaction. Protein expression was quantif ied in myocardial tissue with [H-3]-ryanodine binding and with Western blot s, expressed as densitometric units per microgram of protein (DU), and cell ular localization was visualized with immunohistochemistry. We found mRNA e xpression of isoforms 1, 2, and 3 in cardiomyocytes and myocardial tissue b oth in NF and DCM. Total SR Ca2+-release channel protein expression in NF ( B-max 2.16 +/-0.43 pmol/mg protein) and in DCM (B-max 2.33 +/-0.22 pmol/mg protein) myocardium was unchanged. Expression of isoform 1 of the SR Ca2+-r elease channel was significantly (P=0.0037) increased in DCM myocardium (NF 1.97 +/-0.25 versus DCM 3.37 +/-0.31 DU), whereas protein expression of is oform 2 (NF 14.62 +/-0.87 versus DCM 13.52 +/-0.43 DU) and isoform 3 (NF 1. 39 +/-0.13 versus DCM 1.35 +/-0.19 DU) was unchanged. All 3 isoforms of the protein could be localized in human ventricular myocytes with fluorescence immunohistochemistry. Conclusions-All 3 isoforms of the SR Ca2+-release channel were determined i n human ventricular cardiomyocytes. Increased expression of isoform 1 of th e SR Ca2+-release channel could contribute to impaired excitation-contracti on coupling in human heart failure.