Citations

Rationale: Most cardiac ryanodine receptor (RyR2) mutations associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) are postulated to cause a distinctive form of Ca 2+ release dysfunction. Considering the spread distribution of CPVT mutations, we hypothesized that dysfunctional heterogeneity also was feasible. Objective: To determine the molecular and cellular mechanisms by which a novel RyR2-V2475F mutation associated with CPVT in humans triggers Ca 2+ -dependent arrhythmias in whole hearts and intact mice. Methods and Results: Recombinant channels harboring CPVT-linked RyR2 mutations were functionally characterized using tritiated ryanodine binding and single-channel recordings. Homologous recombination was used to generate a knock-in mouse bearing the RyR2-V2475F mutation. Ventricular myocytes from mice heterozygous for the mutation (RyR2-V2475F +/− ) and their wild-type littermates were Ca 2+ -imaged by confocal microscopy under conditions that mimic stress. The propensity of wild-type and RyR2-V2475F +/− mice to have development of arrhythmias was tested at the whole heart level and in intact animals. Recombinant RyR2-V2475F channels displayed increased cytosolic Ca 2+ activation, abnormal protein kinase A phosphorylation, and increased activation by luminal Ca 2+ . The RyR2-V2475F mutation appears embryonic-lethal in homozygous mice, but heterozygous mice have no alterations at baseline. Spontaneous Ca 2+ release events were more frequent and had shorter latency in isoproterenol-stimulated cardiomyocytes from RyR2-V2475F +/− hearts, but their threshold was unchanged with respect to wild-type. Adrenergically triggered tachyarrhythmias were more frequent in RyR2-V2475F +/− mice. Conclusions: The mutation RyR2-V2475F is phenotypically strong among other CPVT mutations and produces heterogeneous mechanisms of RyR2 dysfunction. In living mice, this mutation appears too severe to be harbored in all RyR2 channels but remains undetected under basal conditions if expressed at relatively low levels. β-adrenergic stimulation breaks the delicate Ca 2+ equilibrium of RyR2-V2475F +/− hearts and triggers life-threatening arrhythmias.

In heart failure (HF), the cardiac hormone natriuretic peptides (NPs) atrial (ANP), B-type (BNP), and C-type (CNP) play a key role to protect cardiac remodeling. The proprotein convertases corin and furin process their respective pro-NPs into active NPs. Here we define in a canine model of HF furin and corin gene and protein expression in normal and failing left atrium (LA) or ventricle (LV) testing the hypothesis that the NP proproteins convertases production is altered in experimental HF. Experimental canine HF was produced by rapid right ventricular pacing for 10 days. NPs, furin, and corin mRNA expression were determined by quantitative RT-PCR. Protein concentration or expression was determined by immunostaining, radioimmunoassay, or Western blot. Furin and corin proteins were present in normal canine LA and LV myocardium and vasculature and in smooth muscle cells. In normal canines, expression of NPs was dominant in the atrium compared with the ventricle. In experimental early stage HF characterized with marked atrial fibrosis, ANP, BNP, and CNP mRNA, and protein concentrations were higher in HF LA but not HF LV compared with normals. In LA, corin mRNA and protein expressions in HF were lower, whereas furin mRNA and protein expressions were higher than normals. NPs and furin expressions were augmented in the atrium in experimental early stage HF and, conversely, corin mRNA and protein expressions were decreased with atrial remodeling. Selective changes of these NP convertases may have significance in the regulation of pro-NP processing and atrial remodeling in early stage HF.

Drug-associated cues can elicit relapse to drug seeking after abstinence. Studies with extinction–reinstatement models implicate dopamine (DA) in the nucleus accumbens shell (NAshell) and dorsolateral caudate-putamen (dlCPu) in cocaine seeking. However, less is known about their roles in cue-induced opiate seeking after prolonged abstinence. Using a morphine self-administration and abstinence–relapse model, we explored the roles of NAshell and dlCPu DA and the D1/D2-like receptor mechanisms underlying morphine rewarding and/or seeking. Acquisition of morphine self-administration was examined following 6-Hydroxydopamine hydrobromide (6-OHDA) lesions of the NAshell and dlCPu. For morphine seeking, rats underwent 3 weeks’ morphine self-administration followed by 3 weeks’ abstinence from morphine and the training environment. Prior to testing, 6-OHDA, D1 antagonist SCH23390, or D2 antagonist eticlopride was locally injected; then rats were exposed to morphine-associated contextual and discrete cues. Results show that acquisition of morphine self-administration was inhibited by NAshell (not dlCPu) lesions, while morphine seeking was attenuated by lesions of either region, by D1 (not D2) receptor blockade in NAshell, or by blockade of either D1 or D2 receptors in dlCPu. These data indicate a critical role of dopaminergic transmission in the NAshell (via D1-like receptors) and dlCPu (via D1- and D2-like receptors) in morphine seeking after prolonged abstinence.

Snoring is a common phenomenon and results from vibration of the soft tissue structures in the upper airway. Snoring may occur alone or as a sign of upper airway resistance syndrome (UARS) or obstructive sleep apnea syndrome (OSA). Snoring carries social consequences and has been linked to increased risk for cardiovascular disease, although this relationship may be confounded by undiagnosed OSA. UARS is characterized by daytime dysfunction and repetitive respiratory effort-related arousals, episodes of increasingly intense breathing efforts that terminate with an arousal from sleep before a hypopnea (episode of partial airflow reduction) or apnea (episode of complete airflow reduction) occur. There is controversy whether UARS is a distinct clinical entity or part of the OSA spectrum. Long-term cardiovascular consequences of UARS are unclear. Risk factors for snoring and UARS are similar and include obesity, nasal congestion, ingestion of pharyngeal relaxing substances before bed such as alcohol, hypnotics, and skeletal muscle relaxants, and abnormalities of the bony and soft tissue structures of the head and neck. Treatment options for snoring and UARS overlap and include risk factor modifications, oral appliances to advance the mandible during sleep, continuous positive airway pressure, and upper airway surgeries.