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

Abstract

Background - The sarcoplasmic reticulum (SR) Ca2+-release channel plays a key role in the excitation-contraction coupling of cardiac myocytes. Because respective alterations have been reported in human heart failure, we investigated isoform expression of the SR Ca2+-release channel in human hearts from 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 reverse-transcription polymerase chain reaction. Protein expression was quantified in myocardial tissue with [3H]-ryanodine binding and with Western blots, expressed as densitometric units per microgram of protein (DU), and cellular localization was visualized with immunohistochemistry. We found mRNA expression of isoforms 1, 2, and 3 in cardiomyocytes and myocardial tissue both in NF and DCM. Total SR Ca2+-release channel protein expression in NF (Bmax 2.16±0.43 pmol/mg protein) and in DCM (Bmax 2.33±0.22 pmol/mg protein) myocardium was unchanged. Expression of isoform 1 of the SR Ca2+-release 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 isoform 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 in human ventricular cardiomyocytes. Increased expression of isoform 1 of the SR Ca2+-release channel could contribute to impaired excitation-contraction coupling in human heart failure.