Diminished Responsiveness of Gs-Coupled Receptors in Severely Failing Human Hearts: No Difference in Dilated Versus Ischemic Cardiomyopathy

Abstract

In end-stage heart failure, cardiac beta-adrenoceptors are decreased and cardiac Gi protein is increased. We assessed beta-adrenoceptors, G proteins, and effects of several beta-adrenoceptor agonists, histamine, and 5-HT on adenylyl cyclase activity in right and left atria and left ventricles and on left ventricular contractility in six potential heart transplant donors (nonfailing hearts; NFHs) and in nine patients with end-stage dilated cardiomyopathy (DCM) and 11 patients with end-stage ischemic cardiomyopathy (ICM) to establish whether the functional responsiveness of all cardiac Gs-coupled receptors is reduced. Beta-adrenoceptors were reduced in all three tissues; in DCM, beta1-adrenoceptors were more markedly downregulated; in ICM, both beta1- and beta2-adrenoceptors were diminished. In all three tissues, isoprenaline-, terbutaline-, histamine- and 5-HT-induced adenylyl cyclase activation was reduced similarly in DCM and ICM. Moreover, in DCM and ICM, guanosine triphosphate (GTP)- (involving Gs and Gi) activated adenylyl cyclase was significantly diminished, whereas NaF-activated (involving only Gs) and Mn2+-activated (acting at the catalytic unit of the enzyme) adenylyl cyclase was unaltered. Left ventricular positive inotropic responses to beta1- (noradrenaline, dopamine, and dobutamine), beta2- (terbutaline), and beta1- and beta2-adrenoceptors (isoprenaline, adrenaline, and epinine), as well as H2-receptor (histamine) stimulation were significantly reduced. The extent of reduction was not different for each agonist in ICM and DCM. We conclude that in DCM and ICM, functional responsiveness of all cardiac Gs-coupled receptors is similarly reduced.

Updating the Physiology and Pathophysiology of Cardiac Myosin-Binding Protein-C

“…Both the FFR and adrenergic responsiveness are markedly depressed in DCM. 33,34 Moreover, some patients with DCM also demonstrate frequency-dependent incomplete relaxation and diastolic dysfunction. 35 We reported similar frequency-dependent diastolic dysfunction in excitable myocardial strips obtained from patients with LVH and normal EF.…”

Effect of a β2-Adrenoceptor Stimulation on Hyperglycemia-Induced Endothelial Dysfunction

“…Binding studies were performed according to Brodde et al (1998) and OЈHara and Brodde (1984) with two experimental groups of cultured PAECs in passage 3 subjected to 5 mM D-glucose ("normoglycemia") or 20 mM D-glucose (high D-glucose, "hyperglycemia"). After reaching confluence in culture passage 3, PAECs were washed twice with ice-cold phosphate-buffered saline, pelleted, and resuspended in ice-cold 154 mM NaCl solution, centrifuged at 1000 rpm, 5 min, 4°C and resuspended in 1 mM KHCO 3 solution.…”

“…Saturation binding assays were routinely carried out as described previously (Brodde et al, 1998;Dhein et al, 2000) in new disposable polypropylene tubes (Sarstedt, Nü rnberg, Germany). Briefly, (Ϫ)-[ 125 I]iodocyanopindolol (ICYP) and all drugs were prepared in icecold incubation buffer (10 mM Tris, 154 mM NaCl, 0.55 mM ascorbic acid, pH 7.4).…”

“…125 I]ICYP ranging from 5 to 200 pM in a total volume of 250 l for 90 min at 37°C in a shaking water bath (Brodde et al, 1998;Dhein et al, 2000). Incubation was terminated by adding 10 ml of 10 mM Tris, 154 mM NaCl buffer, pH 7.4, to the entire reaction mixture followed by rapid filtration over Whatman GF/C filters.…”

“…Therefore, PAEC membranes were incubated for displacement with ICYP (100 pM ϭ 100,000 cpm; this concentration was used in accordance with previous studies; Dhein et al, 2000;Brodde et al, 1998) and because a saturation of ICYP binding was found in the range of 80 to 100 pM) in presence or absence of 21 concentrations (ranging from 10 Ϫ9 to 10 Ϫ4 M) of the highly selective ␤ 2 -adrenoceptor-antagonist ICI 118,551 (Brodde and Michel, 1999). Specific binding was determined as described above.…”