beta-adrenergic, angiotensin II and endothelin-1 receptors on human failing cardiomyocytes

-adrenergic, angiotensin, and endothelin receptor stimulation results in positive inotropic effect on cardiomyocytes. Cardiac expression of these receptors in failing human heart was studied only in homogenated tissue whereas no studies are available in human isolated myocytes. To study and to compare changes of the expression of -adrenergic (AR), Ang II (ATR), ET-1 (ETR) receptors in human failing hearts we investigated isolated left ventricular cardiomyocytes and homogenated hearts obtained from patients undergoing cardiac transplantation for dilated (DCM, n=5) or ischemic (ICM, n=4) cardiomyopathy. Nonfailing (NF) hearts (n=4), were obtained from tentative organ donors whose hearts were not transplanted for non cardiac reasons. Binding studies were performed by incubating 125I-iodocyanopindolol , 125I-Ang II, 125I-ET-1 (for AR, ATR and ETR respectively) with enzymatically isolated cardyomyocytes (105 cells) or cardiac membranes (60 g protein). Receptors subtypes were characterized in competition studies using selective antagonists for adrenergic 1 (metoprolol) and 2 (ICI118551), for angiotensin AT1 (valsartan) and AT2 (PD123319) and for endothelin ETA (BMS 182517) and ETB (BQ618) receptors. Gene expression was investigated at RT-PCR using specific primers and considering the expression of GAPDH as internal standard. On human failing cardiomyocytes receptor density was not downregulated for endothelin (ETA and ETB) and angiotensin (AT1 and AT2) receptors. AT1 and ETA were largely prevalent in comparison to AT2 and ETB, respectively, both in patients and in NF myocytes. Conversely, both 1 and 2 receptor density was reduced in failing cardiomyocytes with the same balanced 1:2 proportion found in NF cells. AT1 and 1 receptors were significantly downregulated only in homogenated hearts. Binding data were confirmed at mRNA level by RT-PCR studies. In conclusion, in failing myocytes ATR and ETR are not downregulated at variance with AR and no correlation exists among the three groups of receptors so that data found on homogenated hearts are not transferable to isolated cardiomyocytes.