The role of nitric oxide (NO) in the cholinergic regulation of heart rate (HR) recovery from an aspect of simulated exercise was investigated in atria isolated from guinea pig to test the hypothesis that NO may be involved in the cholinergic antagonism of the positive chronotropic response to adrenergic stimulation. Inhibition of NO synthesis with N G -monomethyl-l-arginine (l-NMMA, 100 μM) significantly slowed the time course of the reduction in HR without affecting the magnitude of the response elicited by bath-applied ACh (100 nM) or vagal nerve stimulation (2 Hz). The half-times ( t 1/2 ) of responses were 3.99 ± 0.41 s in control vs. 7.49 ± 0.68 s inl-NMMA ( P < 0.05). This was dependent on prior adrenergic stimulation (norepinephrine, 1 μM). The effect ofl-NMMA was reversed byl-arginine (1 mM; t 1/2 4.62 ± 0.39 s). The calcium-channel antagonist nifedipine (0.2 μM) also slowed the kinetics of the reduction in HR caused by vagal nerve stimulation. However, the t 1/2 for the reduction in HR with antagonists (2 mM Cs + and 1 μM ZD-7288) of the hyperpolarization-activated current were significantly faster compared with control. There was no additional effect ofl-NMMA orl-NMMA+l-arginine on vagal stimulation in groups treated with nifedipine, Cs + , or ZD-7288. We conclude that NO contributes to the cholinergic antagonism of the positive cardiac chronotropic effects of adrenergic stimulation by accelerating the HR response to vagal stimulation. This may involve an interplay between two pacemaking currents (L-type calcium channel current and hyperpolarization-activated current). Whether NO modulates the vagal control of HR recovery from actual exercise remains to be determined.
Background — Evidence indicates that myocardial NO production can modulate contractility, but the source of NO remains uncertain. Here, we investigated the role of a type 1 NO synthase isoform (NOS1), which has been recently localized to the cardiac sarcoplasmic reticulum, in the regulation of basal and β-adrenergic myocardial contraction. Methods and Results — Contraction was assessed in left ventricular myocytes isolated from mice with NOS1 gene disruption (NOS1 −/− mice) and their littermate controls (NOS1 +/+ mice) at 3 stimulation frequencies (1, 3, and 6 Hz) in basal conditions and during β-adrenergic stimulation with isoproterenol (2 nmol/L). In addition, we examined the effects of acute specific inhibition of NOS1 with vinyl- l - N -5-(1-imino-3-butenyl)- l -ornithine (L-VNIO, 500 μmol/L). NOS1 −/− myocytes exhibited greater contraction at all frequencies (percent cell shortening at 6 Hz, 10.7±0.92% in NOS1 −/− myocytes versus 7.21±0.8% in NOS1 +/+ myocytes; P <0.05) with a flat frequency-contraction relationship. Time to 50% relaxation was increased in NOS1 −/− myocytes at all frequencies (at 6 Hz, 26.53±1.4 ms in NOS1 −/− myocytes versus 21.27±1.3 ms in NOS1 +/+ myocytes; P <0.05). L-VNIO prolonged time to 50% relaxation at all frequencies (at 6 Hz, 21.28±1.7 ms in NOS1 +/+ myocytes versus 26.45±1.4 ms in NOS1 +/+ +L-VNIO myocytes; P <0.05) but did not significantly increase basal contraction. However, both NOS1 −/− myocytes and NOS1 +/+ myocytes treated with L-VNIO showed a greatly enhanced contraction in response to β-adrenergic stimulation (percent increase in contraction at 6 Hz, 25.2±10.8 in NOS1 +/+ myocytes, 68.2±11.2 in NOS1 −/− myocytes, and 65.1±13.2 in NOS1 +/+ +L-VNIO myocytes; P <0.05). Conclusions — NOS1 disruption enhances basal contraction and the inotropic response to β-adrenergic stimulation in murine ventricular myocytes. These findings indicate that cardiac NOS1-derived NO plays a significant role in the autocrine regulation of myocardial contractility.
Rating scales are often used to identify children with potential Attention-Deficit/Hyperactivity Disorder (ADHD), yet there are frequently discrepancies between informants which may be moderated by child characteristics. The current study asked whether correspondence between parent and teacher ratings on the Strengths and Weakness of ADHD symptoms and Normal behaviour scale (SWAN) varied systematically with child language ability.Parent and teacher SWAN questionnaires were returned for 200 children (aged 61-81 months); 106 had low language ability (LL) and 94 had typically developing language (TL). After exploring informant correspondence (using Pearson correlation) and the discrepancy between raters, we report inter-class correlation coefficients, to assess inter-rater reliability, and Cohen's kappa, to assess agreement regarding possible ADHD caseness.Correlations between informant ratings on the SWAN were moderate. Children with LL were rated as having increased inattention and hyperactivity relative to children with TL; teachers, however, rated children with LL as having more inattention than parents. Inter-rater reliability of the SWAN was good and there were no systematic differences between the LL and TL groups. Case agreement between parent and teachers was fair; this varied by language group with poorer case agreement for children with LL.Children's language abilities affect the discrepancy between informant ratings of ADHD symptomatology and the agreement between parents and teachers regarding potential ADHD caseness. The assessment of children's core language ability would be a beneficial addition to the ADHD diagnostic process.
We characterized the epicardial activation sequence during a norepinephrine (NE)-induced ventricular arrhythmia in anesthetized pigs and studied factors that modulated it. Subepicardial NE infusion caused the QRS complex to invert within a single beat ( n = 35 animals, 101 observations), and the earliest epicardial activation consistently shifted to the randomly located infusion site ( n = 14). This preceded right atrial activation, whereas the total ventricular epicardial activation time increased from 20 ± 4 to 50 ± 9 ms ( P < 0.01). These events were accompanied by a ventricular tachycardia and a drop in left ventricular pressure, which were fully reversed after the infusion was stopped. Epicardial pacing at the infusion site mimicked all electrical and hemodynamic changes induced by NE. The arrhythmia was prevented by propranolol and abolished by cardiac sympathetic or vagal nerve stimulation. Focal automaticity was computationally reconstructed using a two-dimensional sheet of 256 × 256 resistively coupled ventricular cells, where calcium handling was abnormally high in the central region. We conclude that adrenergic stimulation to a small region of the ventricle elicits triggered automaticity and that computational reconstruction implicates calcium overload. Interventions that reduce spatial inhomogeneities of intracellular calcium may prevent this type of arrhythmia.
Stimulation of nitric oxide (NO) release from the coronary endothelium facilitates myocardial relaxation via a cGMP-dependent reduction in myofilament Ca2+ sensitivity. Recent evidence suggests that NO released by a neuronal NO synthase (nNOS) in the myocardium can also hasten left ventricular relaxation; however, the mechanism underlying these findings is uncertain. Here we show that both relaxation (TR50) and the rate of [Ca2+]i transient decay (tau) are significantly prolonged in field-stimulated or voltage-clamped left ventricular myocytes from nNOS-/- mice and in wild-type myocytes (nNOS+/+) after acute nNOS inhibition. Disabling the sarcoplasmic reticulum abolished the differences in TR50 and tau, suggesting that impaired sarcoplasmic reticulum Ca2+ reuptake may account for the slower relaxation in nNOS-/- mice. In line with these findings, disruption of nNOS (but not of endothelial NOS) decreased phospholamban phosphorylation (P-Ser16 PLN), whereas nNOS inhibition had no effect on TR50 or tau in PLN-/- myocytes. Inhibition of cGMP signaling had no effect on relaxation in either group whereas protein kinase A inhibition abolished the difference in relaxation and PLN phosphorylation by decreasing P-Ser16 PLN and prolonging TR50 in nNOS+/+ myocytes. Conversely, inhibition of type 1 or 2A protein phosphatases shortened TR50 and increased P-Ser16 PLN in nNOS-/- but not in nNOS+/+ myocytes, in agreement with data showing increased protein phosphatase activity in nNOS-/- hearts. Taken together, our findings identify a novel mechanism by which myocardial nNOS promotes left ventricular relaxation by regulating the protein kinase A-mediated phosphorylation of PLN and the rate of sarcoplasmic reticulum Ca2+ reuptake via a cGMP-independent effect on protein phosphatase activity.
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