Cross-talk between cAMP and Ca2+ signalling in cardiac pacemaker cells involves IP3-evoked Ca2+ release and stimulation of adenylyl cyclase 1

Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. Here we investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sinoatrial node (SAN) cells to the α-adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.46 % to 8.17% (P = 0.005) in the presence of 1 μM ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.20 %, ST034307 = 16.32 %; P > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transient amplitude (CaT) generated by 10μM PE in the presence and absence of 1μM ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; P = 0.004), but did not result in an inhibition of CaT amplitude increase in response to PE in atrial cells. The results presented here demonstrate the involvement of AC1 in the downstream response of atrial pacemaker activity to α-adrenoreceptor stimulation and IP3R calcium release.

Dexmedetomidine Induces Microglial Activation and Modulates Microglial M1/M2 Polarization in Attenuation of Chronic Morphine Tolerance in Cancer Pain

The pro-inflammatory (M1) and anti-inflammatory (M2) status of microglial determines the outcome of neuroinflammation, which contributes to the pathogenesis of chronic morphine tolerance. Studies report that α2-adrenoceptor agonist dexmedetomidine exerts anti-inflammatory effects in inhibiting morphine tolerance in normal and neuropathic pain animals, which has not been studied in cancer pain. Therefore, we investigate the effect of intrathecal DEX on morphine tolerance in cancer pain, and whether dexmedetomidine functions via modulating microglial activation and M1/M2 polarization. 54 Wistar rats with intrathecal catheterization were treated by morphine for 10 days. Test groups received intrathecal α2-adrenoceptor agonist dexmedetomidine or antagonist MK-467. The mRNA levels of TLR4 and NF-κB were tested by RT-PCR. The protein levels of TLR4, NF-κB, Iba-1, iNOS, CD206 were quantifed using Western blotting, and IL-10 and TNF-α were examined by ELISA. Dexmedetomidine attenuates mechanical threshold and thermal latency, and increased the expression of TLR4 and NF-κB in morphine tolerance of cancer pain. Dexmedetomidine attenuates mechanical and thermal nociception in morphine tolerance in cancer pain rats. Intrathecal DEX pre-treatment significantly increased the protein levels of microglia maker Iba-1, M2 marker CD206 and anti-inflammatory factor IL-10, while had no evident influence on the pro-inflammatory factor TNF-α and M1 marker iNOS in morphine tolerance. Our findings suggest that intrathecal dexmedetomidine attenuates morphine tolerance in cancer pain via α2-adrenoceptor pathway. Furthermore, dexmedetomidine upregulates TLR4/NF-κB pathway and induces microglia activation in chronic morphine tolerance of cancer pain. The anti-inflammatory effect of dexmedetomidine might be exerted by inducing microglia M2 polarization and increasing anti-inflammatory factor IL-10.

Pediatric tizanidine toxicity reversed with naloxone: a case report

Background Tizanidine, an α-2 adrenoceptor agonist, is widely prescribed for the management of spasticity in adults. Case reports on pediatric tizanidine overdose are limited. Here, we report a case of pediatric tizanidine toxicity that was reversed with naloxone. Case presentation A 3-year-old male presented to the emergency department with lethargy, bradycardia, and bradypnea after accidental ingestion of multiple tizanidine tablets. Improvements in the level of consciousness and respiratory and heart rates were observed after two intravenous administrations of naloxone at a dose of 0.05 and 0.1 mg/kg, respectively. Conclusions This case report provides further evidence regarding the use of naloxone as a viable antidote for centrally acting α-2 receptor agonists and presents additional epidemiologic data on childhood tizanidine poisoning.

Trib1 deficiency causes brown adipose respiratory chain depletion and mitochondrial disorder

Tribbles homolog 1 (TRIB1) belongs to the Tribbles family of pseudokinases, which plays a key role in tumorigenesis and inflammation. Although genome-wide analysis shows that TRIB1 expression is highly correlated with blood lipid levels, the relationship between TRIB1 and adipose tissue metabolism remains unclear. Accordingly, the aim of the present study was to explore the role of TRIB1 on mitochondrial function in the brown adipose tissue (BAT). Trib1-knockout mice were established using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology. The metabolic function of the BAT was induced by a β3-adrenoceptor agonist and the energy metabolism function of mitochondria in the BAT of mice was evaluated. Trib1-knockout mice exhibited obesity and impaired BAT thermogenesis. In particular, Trib1 knockout reduced the ability of the BAT to maintain body temperature, inhibited β3-adrenoceptor agonist-induced thermogenesis, and accelerated lipid accumulation in the liver and adipose tissues. In addition, Trib1 knockout reduced mitochondrial respiratory chain complex III activity, produced an imbalance between mitochondrial fusion and fission, caused mitochondrial structural damage and dysfunction, and affected heat production and lipid metabolism in the BAT. Conversely, overexpression of Trib1 in 3T3-L1 adipocytes increased the number of mitochondria and improved respiratory function. These findings support the role of Trib1 in regulating the mitochondrial respiratory chain and mitochondrial dynamics by affecting mitochondrial function and thermogenesis in the BAT.

Vatinoxan – a new development for the clinical use of α2-adrenoceptor agonists in dogs: part 2

The first article in this two part series explored the pharmacodynamics of vatinoxan as a peripherally acting α2 adrenoceptor agonist, and in this installment the pharmacokinetics of vatinoxan and its effect on coadministered drugs are explored.

Vascular reactivity contributes to adipose tissue remodeling in obesity

Vascular reactivity of adipose tissue (AT) is hypothesized to play an important role in the development of obesity. However, the exact role of vascular reactivity in the development of obesity remains unclear. In this study, we investigated the chronological changes in vascular reactivity and the microenvironments of the visceral AT (VAT) and subcutaneous AT (SAT) in lean and obese mice. Changes in blood flow levels induced by a β-adrenoceptor agonist (isoproterenol) were significantly lower in the VAT of the mice fed a high-fat diet (HFD) for 1 and 12 weeks, compared to those in the VAT of the mice fed a low-fat diet (LFD) for the same period; no significant change was observed in the SAT of any mouse group, suggesting depot-specific vascular reactivity of AT. Consistently, the hypoxic area and the expression of genes associated with angiogenesis and macrophage recruitment were increased in the VAT (but not in the SAT) of mice fed an HFD for 1 week, compared with mice fed an LFD. These changes occurred with no morphological changes, including those related to adipocyte size, AT vessel density, and the diameter and pericyte coverage of the endothelium, suggesting a determinant role of vascular reactivity in the type of AT remodeling. The suppression of vascular reactivity was accompanied by increased endothelin-1 gene expression and extracellular matrix (ECM) stiffness only in the VAT, implying enhanced contractile activities of the vasculature and ECM. The results suggest a depot-specific role of vascular reactivity in AT remodeling during the development of obesity.

Thyroxine Induces Acute Relaxation of Rat Skeletal Muscle Arteries via Integrin αvβ3, ERK1/2 and Integrin-Linked Kinase

Aim: Hyperthyroidism is associated with a decreased peripheral vascular resistance, which could be caused by the vasodilator genomic or non-genomic effects of thyroid hormones (TH). Non-genomic, or acute, effects develop within several minutes and involve a wide tissue-specific spectrum of molecular pathways poorly studied in vasculature. We aimed to investigate the mechanisms of acute effects of TH on rat skeletal muscle arteries.Methods: Sural arteries from male Wistar rats were used for isometric force recording (wire myography) and phosphorylated protein content measurement (Western blotting).Results: Both triiodothyronine (T3) and thyroxine (T4) reduced contractile response of sural arteries to α1-adrenoceptor agonist methoxamine. The effect of T4 was more prominent than T3 and not affected by iopanoic acid, an inhibitor of deiodinase 2. Endothelium denudation abolished the effect of T3, but not T4. Integrin αvβ3 inhibitor tetrac abolished the effect of T4 in endothelium-denuded arteries. T4 weakened methoxamine-induced elevation of phospho-MLC2 (Ser19) content in arterial samples. The effect of T4 in endothelium-denuded arteries was abolished by inhibiting ERK1/2 activation with U0126 as well as by ILK inhibitor Cpd22 but persisted in the presence of Src- or Rho-kinase inhibitors (PP2 and Y27632, respectively).Conclusion: Acute non-genomic relaxation of sural arteries induced by T3 is endothelium-dependent and that induced by T4 is endothelium-independent. The effect of T4 on α1-adrenergic contraction is stronger compared to T3 and involves the suppression of extracellular matrix signaling via integrin αvβ3, ERK1/2 and ILK with subsequent decrease of MLC2 (Ser19) phosphorylation.