Histamine receptors in the isolated human middle meningeal artery. A comparison with cerebral and temporal arteries

The subtypes of histamine receptors mediating dilatation of human meningeal arteries have been tested in vitro, using "selective" antagonists, and compared with cerebral and temporal arteries previously examined. Dilatory responses were tested after preconstriction with prostaglandin F2 alpha. Both mepyramine and cimetidine caused a parallel shift to the right of the histamine concentration-response curve, suggesting the presence of both H1- and H2-receptors. Combined treatment with mepyramine and cimetidine caused further displacement of the concentration-response curve to the right. Schild analysis indicated pA2 values of 6.3 for cimetidine and 9.8 for mepyramine in situations of near complete blockade of either of the receptors. Both H1- and H2-receptors seem of importance for the histamine-induced dilatation in meningeal arteries and neither appear to dominate. The data considered in conjunction with our previous findings support the finding that experimental histamine-induced headache due to vasodilatation is intracranial of origin.     

Functional coupling between heterologously expressed dopamine D(2) receptors and KCNQ channels

Activation of KCNQ potassium channels by stimulation of co-expressed dopamine D₂ receptors was studied electrophysiologically in Xenopus laevis oocytes and in mammalian cells. To address the specificity of the interaction between D₂-like receptors and KCNQ channels, combinations of KCNQ1–5 channels and D₂-like receptors (D_2L, D₃, and D₄) were investigated in Xenopus oocytes. Activation of either receptor with the selective D₂-like receptor agonist quinpirole (100 nM) stimulated all the KCNQ currents, independently of the subunit combination, indicating a common pathway of receptor-channel interaction. The KCNQ4 current was investigated in further detail and was increased by 19.9±1.6% (n=20) by D_2L receptor stimulation. The effect could be mimicked by injection of GTPS and prevented by injection of Bordetella pertussis toxin, indicating that channel stimulation was mediated via a G protein of the G_i/o subtype. Cells of the human neuroblastoma line SH-SY5Y were co-transfected transiently with KCNQ4 and D_2L receptors. Stimulation of D_2L receptors increased the KCNQ4 current (n=6) as determined in whole-cell patch-clamp recordings. The specificity of the dopaminergic activation of the KCNQ channels was confirmed by co-expression of other neuronal K⁺ channels (BK, K_V1.1, and K_V4.3) with the D_2L receptor in Xenopus oocytes. None of these K⁺ channels responded to stimulation of the D_2L receptor. In the mammalian brain, dopamine D₂ receptors and KCNQ channels co-localise postsynaptically in several brain regions, so modulation of neuronal excitability by dopamine release could in part be mediated via an effect on KCNQ channels.     

IL-2 receptor γ-chain molecule is critical for intestinal T-cell reconstitution in humanized mice

Intestinal immune cells are important in host defense, yet the determinants for human lymphoid homeostasis in the intestines are poorly understood. In contrast, lymphoid homeostasis has been studied extensively in mice, where the requirement for a functional common γ-chain molecule has been established. We hypothesized that humanized mice could offer insights into human intestinal lymphoid homeostasis if generated in a strain with an intact mouse common γ-chain molecule. To address this hypothesis, we used three mouse strains (non-obese diabetic (NOD)/severe-combined immunodeficient (SCID) (N/S); NOD/SCID γ-chain(-/-) (NSG); and Rag2(-/-) γ-chain(-/-) (DKO)) and two humanization techniques (bone marrow liver thymus (BLT) and human CD34(+) cell bone marrow transplant of newborn mice (hu)) to generate four common types of humanized mice: N/S-BLT, NSG-BLT, NSG-hu, and DKO-hu mice. The highest levels of intestinal human T cells throughout the small and large intestines were observed in N/S-BLT mice, which have an intact common γ-chain molecule. Furthermore, the small intestine lamina propria T-cell populations of N/S-BLT mice exhibit a human intestine-specific surface phenotype. Thus, the extensive intestinal immune reconstitution of N/S-BLT mice was both quantitatively and qualitatively better when compared with the other models tested such that N/S-BLT mice are well suited for the analysis of human intestinal lymphocyte trafficking and human-specific diseases affecting the intestines.     

DC-SIGN (CD209), pentraxin 3 and vitamin D receptor gene variants associate with pulmonary tuberculosis risk in West Africans

We investigated the role of DC-SIGN (CD209), long pentraxin 3 (PTX3) and vitamin D receptor (VDR) gene single nucleotide polymorphisms (SNPs) in susceptibility to pulmonary tuberculosis (TB) in 321 TB cases and 347 healthy controls from Guinea-Bissau. Five additional, functionally relevant SNPs within toll-like receptors (TLRs) 2, 4 and 9 were typed but found, when polymorphic, not to affect host vulnerability to pulmonary TB. We did not replicate an association between SNPs in the DC-SIGN promoter and TB. However, we found that two polymorphisms, one in DC-SIGN and one in VDR, were associated in a nonadditive model with disease risk when analyzed in combination with ethnicity (P=0.03 for DC-SIGN and P=0.003 for VDR). In addition, PTX3 haplotype frequencies significantly differed in cases compared to controls and a protective effect was found in association with a specific haplotype (OR 0.78, 95% CI 0.63-0.98). Our findings support previous data showing that VDR SNPs modulate the risk for TB in West Africans and suggest that variation within DC-SIGN and PTX3 also affect the disease outcome.     

Chronic sympathetic activation promotes downregulation of β-adrenoceptor-mediated effects in the guinea pig heart independently of structural remodeling and systolic dysfunction

It is uncertain if downregulation of β-adrenoceptor signaling pathway is promoted by an enhanced adrenergic tone at an early stage of cardiac disease, or it develops secondary to detrimental local myocardial changes in advanced heart failure. We examined the integrity of β-adrenoceptor signaling pathway upon chronic infusion of isoproterenol, a β-adrenoceptor agonist, at a dose producing no structural left ventricular (LV) remodeling and systolic dysfunction. Subcutaneous isoproterenol infusion (400 μg kg⁻¹ h⁻¹ over 16 days) to guinea pigs using osmotic minipumps produced no change in cardiac weights, LV internal dimensions, myocyte cross-sectional area, extent of interstitial fibrosis, and basal contractile function. Isolated, perfused heart preparations from isoproterenol-treated guinea pigs exhibited attenuated responsiveness to acute β-adrenoceptor stimulation, as evidenced by reduced LV developed pressure increase, less shortening of LV epicardial monophasic action potential and effective refractory period, and less myocardial cyclic adenosine monophosphate elevation, in response to isoproterenol exposure, when compared to saline-treated controls. Pharmacological responses to forskolin, an activator of the adenylate cyclase catalytic subunit, were well preserved in isoproterenol-treated hearts. Downregulation of β-adrenoceptor-mediated effects upon chronic isoproterenol infusion was associated with markedly reduced stimulatory G-protein α-subunit (G_sα) myocardial expression levels. No change in expression levels of β-adrenoceptors, G-protein-coupled receptor kinase 2, inhibitory G-protein α-subunit (G_iα2), and Ca_v1.2 and K_v7.1 ion channels was determined in isoproterenol-treated hearts. We therefore conclude that sustained adrenergic overstimulation may promote downregulation of myocardial β-adrenoceptor-mediated effects independently of structural LV remodeling and systolic failure, an effect attributed to β-adrenoceptor uncoupling from adenylate cyclase due to reduced G_sα-protein expression.     

Perspectives for clinical measures of dynamic foot function—Reference data and methodological considerations

Several studies have investigated if static posture assessments qualify to predict dynamic function of the foot showing diverse outcomes. However, it was suggested that dynamic measures may be better suited to predict foot-related overuse problems. The purpose of this study was to establish the reliability for dynamic measures of longitudinal arch angle (LAA) and navicular height (NH) and to examine to what extent static and dynamic measures thereof are related. Intra-rater reliability of LAA and NH measures was tested on a sample of 17 control subjects. Subsequently, 79 subjects were tested while walking on a treadmill. The ranges and minimum values for LAA and NH during ground contact were identified over 20 consecutive steps. A geometric error model was used to simulate effects of marker placement uncertainty and skin movement artifacts. Results demonstrated the highest reliability for the minimum NH (MinNH), followed by the minimum LAA (MinLAA), the dynamic range of navicular height (ΔNH) and the range of LAA (ΔLAA) while all measures were highly reliable. Marker location uncertainty and skin movement artifacts had the smallest effects on measures of NH. The use of an alignment device for marker placement was shown to reduce error ranges for NH measures. Therefore, ΔNH and MinNH were recommended for functional dynamic foot characterization in the sagittal plane. There is potential for such measures to be a suitable predictor for overuse injuries while being obtainable in clinical settings. Future research needs to include such dynamic but simple foot assessments in large-scale clinical studies.     

Combined inhibition of nitric oxide and prostaglandins reduces human skeletal muscle blood flow during exercise

The vascular endothelium is an important mediator of tissue vasodilatation, yet the role of the specific substances, nitric oxide (NO) and prostaglandins (PG), in mediating the large increases in muscle perfusion during exercise in humans is unclear. Quadriceps microvascular blood flow was quantified by near infrared spectroscopy and indocyanine green in six healthy humans during dynamic knee extension exercise with and without combined pharmacological inhibition of NO synthase (NOS) and PG by l -NAME and indomethacin, respectively. Microdialysis was applied to determine interstitial release of PG. Compared to control, combined blockade resulted in a 5- to 10-fold lower muscle interstitial PG level. During control incremental knee extension exercise, mean blood flow in the quadriceps muscles rose from 10 ± 0.8 ml (100 ml tissue)⁻¹ min⁻¹ at rest to 124 ± 19, 245 ± 24, 329 ± 24 and 312 ± 25 ml (100 ml tissue)⁻¹ min⁻¹ at 15, 30, 45 and 60 W, respectively. During inhibition of NOS and PG, blood flow was reduced to 8 ± 0.5 ml (100 ml tissue)⁻¹ min⁻¹ at rest, and 100 ± 13, 163 ± 21, 217 ± 23 and 256 ± 28 ml (100 ml tissue)⁻¹ min⁻¹ at 15, 30, 45 and 60 W, respectively ( P < 0.05 vs. control). In conclusion, combined inhibition of NOS and PG reduced muscle blood flow during dynamic exercise in humans. These findings demonstrate an important synergistic role of NO and PG for skeletal muscle vasodilatation and hyperaemia during muscular contraction.     

Atrial fibrillation: the role of common and rare genetic variants

Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting 1–2% of the general population. A number of studies have demonstrated that AF, and in particular lone AF, has a substantial genetic component. Monogenic mutations in lone and familial AF, although rare, have been recognized for many years. Presently, mutations in 25 genes have been associated with AF. However, the complexity of monogenic AF is illustrated by the recent finding that both gain- and loss-of-function mutations in the same gene can cause AF. Genome-wide association studies (GWAS) have indicated that common single-nucleotide polymorphisms (SNPs) have a role in the development of AF. Following the first GWAS discovering the association between PITX2 and AF, several new GWAS reports have identified SNPs associated with susceptibility of AF. To date, nine SNPs have been associated with AF. The exact biological pathways involving these SNPs and the development of AF are now starting to be elucidated. Since the first GWAS, the number of papers concerning the genetic basis of AF has increased drastically and the majority of these papers are for the first time included in a review. In this review, we discuss the genetic basis of AF and the role of both common and rare genetic variants in the susceptibility of developing AF. Furthermore, all rare variants reported to be associated with AF were systematically searched for in the Exome Sequencing Project Exome Variant Server.