Mechanical unloading restores beta-adrenergic responsiveness and reverses receptor downregulation in the failing human heart.

BACKGROUND: Mechanical unloading of the failing human heart with a left ventricular assist device (LVAD) results in clinically documented reversal of chamber dilation and improvement of cardiac function. We tested the hypothesis that LVAD support normalizes the ability of cardiac muscle to respond to sympathetic nervous system stimulation by reversing the downregulation of beta-adrenergic receptors. METHODS AND RESULTS: Human LV tissue was obtained from nonfailing hearts of unmatched organ donors and failing hearts at the time of transplantation, with or without LVAD. Baseline contractile parameters and inotropic response to a beta-adrenergic agonist were measured in isolated trabecular muscles. beta-Adrenergic receptor density was quantified by radioligand binding. Results showed a significant increase in the response to beta-adrenergic stimulation after LVAD (developed tension increased by 0.76+/-0.09 g/mm(2) in nonfailing, 0.38+/-0.07 in failing, and 0.68+/-0.10 in failing+LVAD; P<0.01), accompanied by an increased density of beta-adrenergic receptors (58.7+/-9.6 fmol/mg protein in nonfailing, 26.2+/-3.8 in failing, and 63.0+/-8.3 in failing+LVAD; P<0.05). These changes were unrelated to the duration of support. CONCLUSIONS: Data demonstrate that mechanically supporting the failing human heart with an LVAD can reverse the downregulation of beta-adrenergic receptors and restore the ability of cardiac muscle to respond to inotropic stimulation by the sympathetic nervous system. This indicates that functional impairment of cardiac muscle in human heart failure is reversible.

The effects of propofol on the contractility of failing and nonfailing human heart muscles.

We determined the direct effects of propofol on the contractility of human nonfailing atrial and failing atrial and ventricular muscles. Atrial and ventricular trabecular muscles were obtained from the failing human hearts of transplant patients or from nonfailing hearts of patients undergoing coronary artery bypass surgery. Isometric contraction variables were recorded before and after propofol was added to the bath in concentrations between 0.056 and 560 microM. The effects of propofol were compared with its commercial vehicle intralipid. To test beta-adrenergic effects in the presence of propofol, 1 microM isoproterenol was added at the end of each experiment. To determine the cellular mechanisms responsible for the actions of propofol, we examined its effects on actomyosin ATPase activity and sarcoplasmic reticulum (SR) Ca(2+) uptake in nonfailing atrial tissues. Propofol caused a concentration-dependent decrease in maximal developed tension in all muscles, which became significant (P < 0.05) at concentrations exceeding the clinical range (> or =56 microM). Isoproterenol restored contractility to the level achieved before exposure to propofol (P > 0.05 compared with baseline). Failing ventricular muscle exposed to propofol exhibited somewhat diminished ability to recover contractility in response to isoproterenol (P < 0.05 versus failing muscle exposed to intralipid only). Propofol induced a concentration-dependent decrease in the uptake of Ca(2+) into SR vesicles. At the same time, in the presence of 56 microM propofol, the Ca(2+)-activated actomyosin ATPase activity was shifted leftward, demonstrating an increase in myofilament sensitivity to Ca(2+). We conclude that propofol exerts a direct negative inotropic effect in nonfailing and failing human myocardium, but only at concentrations larger than typical clinical concentrations. Negative inotropic effects are reversible with beta-adrenergic stimulation. The negative inotropic effect of propofol is at least partially mediated by decreased Ca(2+) uptake into the SR; however, the net effect of propofol on contractility is insignificant at clinical concentrations because of a simultaneous increase in the sensitivity of the myofilaments to activator Ca(2+).

The effects of etomidate on the contractility of failing and nonfailing human heart muscle.

UNLABELLED: We measured the effects of etomidate on contractility of human cardiac muscle. Muscles were obtained from the left ventricle and right atrium of 12 patients undergoing cardiac transplantation, and from the right atrium of 12 patients undergoing coronary artery bypass surgery. Muscles were studied at 37 degrees C and 1.0 Hz. Variables of isometric contraction were recorded before and after etomidate (0.04-80 microM) or its solvent, propylene glycol. The ability of beta-adrenergic stimulation to cause an inotropic effect after etomidate was also assessed. Etomidate caused a dose-dependent decrease in developed tension, which was statistically significant only at concentrations exceeding clinical doses (> or =20 microM; P < 0. 05). Decreases in maximum rates of contraction and relaxation paralleled changes in developed tension. beta-Adrenergic stimulation reversed the etomidate-induced decreases in developed tension and rates of contraction and relaxation to baseline (P > 0.05 compared with baseline). Thus, in human myocardium, etomidate exerts a dose-dependent negative inotropic effect, which is reversible with beta-adrenergic stimulation. Concentrations required to produce these negative inotropic effects are, however, in excess of those reached during clinical use. Therefore, etomidate-induced negative inotropy is unlikely to be a problem clinically, even in patients with cardiac dysfunction. IMPLICATIONS: Etomidate produced a similar dose-dependent negative inotropic effect in both failing and nonfailing human myocardium. This effect was present only at concentrations exceeding those attained clinically and was reversible with beta-adrenergic stimulation.

The human phospholamban gene: structure and expression.

Phospholamban, through modulation of sarcoplasmic reticulum calcium-ATPase activity, is a key regulator of cardiac diastolic function. Alterations in phospholamban expression may define parameters of muscle relaxation. In experimental animals, phospholamban is differentially expressed in various striated and smooth muscles, and within the four chambers of the heart. Decreased phospholamban expression within the heart during heart failure has also been observed. Furthermore, regulatory elements of mammalian phospholamban genes remain poorly defined. To extend these studies to humans, we (1) characterized phospholamban expression in various human organs, (2) isolated genomic clones encoding the human phospholamban gene, and (3) prepared human phospholamban promoter/luciferase reporter constructs and performed transient transfection assays to begin identification of regulatory elements. We observed that human ventricle and quadriceps displayed high levels of phospholamban transcripts and proteins, with markedly lower expression observed in smooth muscles, while the right atria also expressed low levels of phospholamban. The human phospholamban gene structure closely resembles that reported for chicken, rabbit, rat, and mouse. Comparison of the human to other mammalian phospholamban genes indicates a marked conservation of sequence for at least 217 bp upstream of the transcription start site, which contains conserved motifs for GATA, CP1/NFY, M-CAT-like, and E-box elements. Transient transfection assays with a series of plasmids containing deleted 5' flanking regions (between -2530 and -66 through +85) showed that sequences between -169 and the CP1-box at -93 were required for maximal promoter activity in neonatal rat cardiomyocytes. Activity of these reporters in HeLa cells was markedly lower than that observed in rat cardiomyocytes, suggesting at least a partial tissue selectivity of these reporter constructs.