Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts.

Cardiac contractility is regulated by several neural, hormonal, paracrine, and autocrine factors. Amongst these, signaling through β-adrenergic and serotonin receptors generates the second messenger cyclic AMP (cAMP), whereas activation of natriuretic peptide receptors and soluble guanylyl cyclases generates cyclic GMP (cGMP). Both cyclic nucleotides regulate cardiac contractility through several mechanisms.

CNP regulates cardiac contractility and increases cGMP near both SERCA and TnI: difference from BNP visualized by targeted cGMP biosensors.

Aims: Guanylyl cyclase-B (GC-B; natriuretic peptide receptor-B, NPR-B) stimulation by C-type natriuretic peptide (CNP) increases cGMP and causes a lusitropic and negative inotropic response in adult myocardium. These effects are not mimicked by NPR-A (GC-A) stimulation by brain natriuretic peptide (BNP), despite similar cGMP increase. More refined methods are needed to better understand the mechanisms of the differential cGMP signalling and compartmentation.

Exercise Training Stabilizes RyR2-Dependent Ca Release in Post-infarction Heart Failure.

Dysfunction of the cardiac ryanodine receptor (RyR2) is an almost ubiquitous finding in animal models of heart failure (HF) and results in abnormal Ca release in cardiomyocytes that contributes to contractile impairment and arrhythmias. We tested whether exercise training (ET), as recommended by current guidelines, had the potential to stabilize RyR2-dependent Ca release in rats with post-myocardial infarction HF. We subjected male Wistar rats to left coronary artery ligation or sham operations.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function.

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors.

An inactive receptor-G protein complex maintains the dynamic range of agonist-induced signaling.

Agonist binding promotes activation of G protein-coupled receptors (GPCRs) and association of active receptors with G protein heterotrimers. The resulting active-state ternary complex is the basis for conventional stimulus-response coupling. Although GPCRs can also associate with G proteins before agonist binding, the impact of such preassociated complexes on agonist-induced signaling is poorly understood.

FRET-based cyclic GMP biosensors measure low cGMP concentrations in cardiomyocytes and neurons.

Several FRET (fluorescence resonance energy transfer)-based biosensors for intracellular detection of cyclic nucleotides have been designed in the past decade. However, few such biosensors are available for cGMP, and even fewer that detect low nanomolar cGMP concentrations. Our aim was to develop a FRET-based cGMP biosensor with high affinity for cGMP as a tool for intracellular signaling studies.

Constitutive inhibitory G protein activity upon adenylyl cyclase-dependent cardiac contractility is limited to adenylyl cyclase type 6.

Purpose: We previously reported that inhibitory G protein (Gi) exerts intrinsic receptor-independent inhibitory activity upon adenylyl cyclase (AC) that regulates contractile force in rat ventricle. The two major subtypes of AC in the heart are AC5 and AC6. The aim of this study was to determine if this intrinsic Gi inhibition regulating contractile force is AC subtype selective.

Reduced ambient temperature exacerbates SIRS-induced cardiac autonomic dysregulation and myocardial dysfunction in mice.

Sepsis-induced myocardial depression (SIMD) is an early and frequent consequence of the infection-induced systemic inflammatory response syndrome. In homiotherms, variations in ambient temperature (T) outside the thermoneutral zone induce thermoregulatory responses mainly driven by a gradually increased sympathetic activity, which may affect disease severity. We hypothesized that thermoregulatory responses upon reduced T exposition aggravate SIMD in mice.

Knockout of adenylyl cyclase isoform 5 or 6 differentially modifies the β-adrenoceptor-mediated inotropic response.

Although only β-adrenergic receptors (βAR) dually couple with stimulatory G protein (G) and inhibitory G protein (G), inactivation of G enhances both βAR and βAR responsiveness. We hypothesize that G restrains spontaneous adenylyl cyclase (AC) activity independent of receptor activation. Subcellular localization of the AC5/6 subtypes varies contributing to the compartmentation of βAR signaling.

Preassociation between the 5-HT serotonin receptor and G protein G: molecular determinants and association with low potency activation of adenylyl cyclase.

According to early models of GPCR signaling, G proteins only interact with activated receptors. However, some GPCRs were shown to assemble with G proteins before receptor activation, in accordance with more recent models. Previously, we found that the 5-HT receptor, as opposed to the 5-HT receptor, was preassociated with G, but the molecular determinants for this interaction are still elusive.

Hypothermia elongates the contraction-relaxation cycle in explanted human failing heart decreasing the time for ventricular filling during diastole.

Targeted temperature management is part of the standardized treatment for patients in cardiac arrest. Hypothermia decreases cerebral oxygen consumption and induces bradycardia; thus, increasing the heart rate may be considered to maintain cardiac output. We hypothesized that increasing heart rate during hypothermia would impair diastolic function.

Related GPCRs couple differently to G: preassociation between G protein and 5-HT serotonin receptor reveals movement of Gα upon receptor activation.

How GPCRs and G proteins interact is important for their biologic functions and their functions as pharmacologic targets. It is still an open question whether receptors and G proteins are preassembled in a complex or interact only after receptor activation. We compared the propensity of the two G-coupled serotonin (5-HT) receptors 5-HT and 5-HT to associate with G protein prior to agonist activation.

PDE3 inhibition by C-type natriuretic peptide-induced cGMP enhances cAMP-mediated signaling in both non-failing and failing hearts.

We have previously shown that the natriuretic peptide receptor B (NPR-B) agonist C-type natriuretic peptide (CNP) enhances cyclic adenosine 3´,5´-monophosphate (cAMP)-mediated signaling in failing hearts, through cyclic guanosine 3´,5´-monophosphate (cGMP)-mediated phosphodiesterase (PDE) 3 inhibition. As several signaling pathways are importantly changed in failing hearts, it could not be taken for granted that this crosstalk would be the same in non-failing hearts. Thus, we wanted to clarify to which extent this effect of CNP occurred also in non-failing hearts.

Functional pharmacological characterization of SER100 in cardiovascular health and disease.

Background And Purpose: SER100 is a selective nociceptin (NOP) receptor agonist with sodium-potassium-sparing aquaretic and anti-natriuretic activity. This study was designed to characterize the functional cardiovascular pharmacology of SER100 in vitro and in vivo, including experimental models of cardiovascular disease.

Experimental Approach: Haemodynamic, ECG parameters and heart rate variability (HRV) were determined using radiotelemetry in healthy, conscious mice.

CaMKII and at least two unidentified kinases phosphorylate regulatory light chain in non-contracting cardiomyocytes.

In cardiac tissue, regulatory light chain (RLC, myosin light chain 2) phosphorylation (Ser(15)) leads to modulation of muscle contraction through Ca(2+)-sensitization. To elucidate which kinases that are involved in the basal (diastolic phase) RLC phosphorylation, we studied non-contracting adult rat cardiomyocytes. RLC kinase activities in situ were unmasked by maximally inhibiting myosin light chain phosphatase (MLCP) by calyculin A in the absence and presence of various protein kinase inhibitors.

CaMKII in addition to MLCK contributes to phosphorylation of regulatory light chain in cardiomyocytes.

The aim was to identify kinase activities involved in the phosphorylation of regulatory light chain (RLC) in situ in cardiomyocytes. In electrically stimulated rat cardiomyocytes, phosphatase inhibition by calyculin A unmasked kinase activities evoking an increase of phosphorylated RLC (P-RLC) from about 16% to about 80% after 80 min. The phosphorylation rate in cardiomyocytes was reduced by about 40% by the myosin light chain kinase (MLCK) inhibitor, ML-7.

Low β₂-adrenergic receptor level may promote development of castration resistant prostate cancer and altered steroid metabolism.

The underlying mechanisms responsible for the development of castration-resistant prostate cancer (CRPC) in patients who have undergone androgen deprivation therapy are not fully understood. This is the first study to address whether β2-adrenergic receptor (ADRB2)- mediated signaling may affect CRPC progression in vivo. By immunohistochemical analyses, we observed that low levels of ADRB2 is associated with a more rapid development of CRPC in a Norwegian patient cohort.

The inotropic effect of the active metabolite of levosimendan, OR-1896, is mediated through inhibition of PDE3 in rat ventricular myocardium.

Aims: We recently published that the positive inotropic response (PIR) to levosimendan can be fully accounted for by phosphodiesterase (PDE) inhibition in both failing human heart and normal rat heart. To determine if the PIR of the active metabolite OR-1896, an important mediator of the long-term clinical effects of levosimendan, also results from PDE3 inhibition, we compared the effects of OR-1896, a representative Ca2+ sensitizer EMD57033 (EMD), levosimendan and other PDE inhibitors.

Methods: Contractile force was measured in rat ventricular strips.

Downregulation of 5-HT7 Serotonin Receptors by the Atypical Antipsychotics Clozapine and Olanzapine. Role of Motifs in the C-Terminal Domain and Interaction with GASP-1.

The human 5-HT7 serotonin receptor, a G-protein-coupled receptor (GPCR), activates adenylyl cyclase constitutively and upon agonist activation. Biased ligands differentially activate 5-HT7 serotonin receptor desensitization, internalization and degradation in addition to G protein activation. We have previously found that the atypical antipsychotics clozapine and olanzapine inhibited G protein activation and, surprisingly, induced both internalization and lysosomal degradation of 5-HT7 receptors.