Clinical trials and experimental animal studies have confirmed the contribution of arterial baroreflex impairment in causing excess morbidity and mortality in type-1 diabetes. Our previous study has shown that angiotensin II (Ang II)-NADPH oxidase-superoxide signaling is associated with the reduced cell excitability in the aortic baroreceptor neurons (a primary afferent limb of the arterial baroreflex) from diabetic rats. In this study, we examined whether above-mentioned signaling might contribute to the blunted baroreflex sensitivity in streptozotocin-induced diabetic rats. Using Ang II 125I radioimmunoassay and lucigenin chemiluminescence method, we found Ang II concentration, NADPH oxidase activity, and superoxide production in the nodose ganglia were enhanced in diabetic rats, compared to sham rats. As an index of the arterial baroreflex sensitivity, the reflex decreases in blood pressure and heart rate evoked by unilateral steady-frequency aortic depressor nerve stimulation were attenuated in diabetic rats. Local microinjection (50 nl) of losartan (an AT1 receptor antagonist, 1 nmol), apocynin (a NADPH oxidase inhibitor, 1 nmol), and tempol (a superoxide dismutase mimetic, 10 nmol) into the nodose ganglia significantly improved the arterial baroreflex sensitivity in diabetic rats. In addition, these three chemicals also normalized exogenous Ang II-attenuated arterial baroreflex sensitivity in sham rats. These results indicate that overactivation of the Ang II-NADPH oxidase-superoxide signal pathway in the nodose ganglia contributes to the blunted baroreflex sensitivity in diabetes.
Angiotensin II; Baroreflex; Diabetes; NADPH oxidase; Superoxide
Voltage-gated sodium (Nav) channels are responsible for initiation and propagation of action potential in the neurons. To explore the mechanisms for chronic heart failure (CHF)-induced baroreflex dysfunction, we measured the expression and current density of Nav channel subunits (Nav1.7, Nav1.8, and Nav1.9) in the aortic baroreceptor neurons and investigated the role of Nav channels on aortic baroreceptor neuron excitability and baroreflex sensitivity in sham and CHF rats. CHF was induced by left coronary artery ligation. The development of CHF (6–8 weeks after the coronary ligation) was confirmed by hemodynamic and morphological characteristics. Immunofluorescent data indicated that Nav1.7 was expressed in A-type (myelinated) and C-type (unmyelinated) nodose neurons but Nav1.8 and Nav1.9 were expressed only in C-type nodose neurons. Real-time RT-PCR and western blot data showed that CHF reduced mRNA and protein expression levels of Nav channels in nodose neurons. In addition, using the whole cell patch-clamp technique, we found that Nav current density and cell excitability of the aortic baroreceptor neurons were lower in CHF rats than that in sham rats. Aortic baroreflex sensitivity was blunted in anesthetized CHF rats, compared with that in sham rats. Furthermore, Nav channel activator (rATX II, 100 nM) significantly enhanced Nav current density and cell excitability of aortic baroreceptor neurons and improved aortic baroreflex sensitivity in CHF rats. These results suggest that reduced expression and activation of the Nav channels is involved in the attenuation of baroreceptor neuron excitability, which subsequently contributes to the impairment of baroreflex in CHF state.
Aortic baroreceptor neuron; Baroreflex; Heart failure; Sodium channel
The generation of action potential is required for stimulus-evoked neurotransmitter release in most neurons. Although various voltage-gated ion channels are involved in action potential production, the initiation of the action potential is mainly mediated by voltage-gated Na+ channels. In the present study, differentiation-induced changes of mRNA and protein expression of Na+ channels, Na+ currents, and cell membrane excitability were investigated in NG108-15 cells.
Whole-cell patch-clamp results showed that differentiation (9 days) didn’t change cell membrane excitability, compared to undifferentiated state. But differentiation (21 days) induced the action potential generation in 45.5% of NG108-15 cells (25/55 cells). In 9-day-differentiated cells, Na+ currents were mildly increased, which was also found in 21-day differentiated cells without action potential. In 21-day differentiated cells with action potential, Na+ currents were significantly enhanced. Western blot data showed that the expression of Na+ channels was increased with differentiated-time dependent manner. Single-cell real-time PCR data demonstrated that the expression of Na+ channel mRNA was increased by 21 days of differentiation in NG108-15 cells. More importantly, the mRNA level of Na+ channels in cells with action potential was higher than that in cells without action potential.
Differentiation induces expression of voltage-gated Na+ channels and action potential generation in NG108-15 cells. A high level of the Na+ channel density is required for differentiation-triggered action potential generation.
Action potential; Na+ channel; NG108-15 cell; Patch clamp; Single-cell real-time PCR; Western blot
The title compound, C5H8ClNO3, was prepared by the nucleophilic substitution reaction of (2S)-2-chloropropanoyl chloride with glycine. The acetate group forms a dihedral angle of 84.6 (1)° with the mean plane of the C—NH—C=O fragment. In the crystal, the molecules are linked by N—H⋯O and O—H⋯O hydrogen bonds, generating a three-dimensional network, which consolidates the crystal packing.
In the title compound, C29H26N2O4, the benzene ring is twisted by 73.5 (5) and 84.9 (3)° with respect to the mean planes of the two indole ring systems; the mean planes of the indole ring systems are oriented at a dihedral angle of 82.0 (5)°. In the crystal, molecules are linked by pairs of N—H⋯O hydrogen bonds into chains.
Although arterial limb tourniquet is one of the first-line treatments to prevent exsanguinating hemorrhage in both civilian pre-hospital and battlefield casualty care, prolonged application of a limb tourniquet can lead to serious ischemia-reperfusion injury. However, the underlying pathomechanisms of tourniquet-induced ischemia-reperfusion injury are still poorly understood. Using a murine model of acute limb ischemia-reperfusion, we investigated if acute limb ischemia-reperfusion injury is mediated by superoxide overproduction and mitochondrial dysfunction. Hind limbs of C57/BL6 mice were subjected to 3 h ischemia and 4 h reperfusion via placement and release of a rubber tourniquet at the greater trochanter. Approximately 40% gastrocnemius muscle suffered infarction in this model. Activities of mitochondrial electron transport chain complexes including complex I, II, III, and IV in gastrocnemius muscle were decreased in the ischemia-reperfusion group compared to sham. Superoxide production was increased while activity of manganese superoxide dismutase (MnSOD, the mitochondria-targeted SOD isoform) was decreased in the ischemia-reperfusion group compared to sham group. Pretreatment with tempol (a SOD mimetic, 50 mg/kg) or co-enzyme Q10 (50 mg/kg) not only decreased the superoxide production, but also reduced the infarct size and normalized mitochondrial dysfunction in the gastrocnemius muscle. Our results suggest that tourniquet-induced skeletal muscle ischemia-reperfusion injuries including infarct size and mitochondrial dysfunction may be mediated via the superoxide over-production and reduced antioxidant activity. In the future, this murine ischemia-reperfusion model can be adapted to mechanistically evaluate anti-ischemic molecules in tourniquet-induced skeletal muscle injury.
Infarct size; Ischemia-reperfusion injury; Mitochondria; Superoxide; Tourniquet
In the molecule of the title compound, C15H12ClF2NO3, the quinoline ring system is not planar, the dihedral angle between the pyridine and benzene rings being 3.55 (8)°. In the crystal, intermolecular C—H⋯O hydrogen bonds link the molecules into layers parallel to (101).
In the title compound, C14H10N2O2, the dihedral angle between the heterocyclic ring system and the phenyl ring is 45.8 (5)°. Weak intermolecular C—H⋯N hydrogen bonding is present in the crystal structure.
Chronic exposure to intermittent hypoxia (CIH) increases carotid sinus nerve activity in normoxia and in response to acute hypoxia. We hypothesized that CIH augments basal and chemoreflex-stimulated sympathetic outflow through an angiotensin receptor-dependent mechanism. Rats were exposed to CIH for 28 days: a subset was treated with losartan. Then, lumbar sympathetic activity was recorded under anesthesia during 20-second apneas, isocapnic hypoxia, and potassium cyanide. We measured carotid body superoxide production and expression of angiotensin II type-1 receptor, neuronal nitric oxide synthase, and NADPH oxidase. Sympathetic activity was higher in CIH vs. control rats at baseline, during apneas and isocapnic hypoxia, but not cyanide. Carotid body superoxide production and expression of angiotensin II type 1 receptor and gp91phox subunit of NADPH oxidase were elevated in CIH rats, whereas expression of neuronal nitric oxide synthase was reduced. None of these differences were evident in animals treated with losartan. CIH-induced augmentation of chemoreflex sensitivity occurs, at least in part, via the renin-angiotensin system.
chemoreceptors; angiotensin II; superoxide; angiotensin antagonist; oxidative stress
The title compound, C19H16FNO, crystallizes with two independent molecules in the asymmetric unit. In the two molecules, the dihedral angles between the benzene and quinoline rings are 72.6 (5) and 76.2 (5)°, between the cyclopropane and quinoline rings they are 65.2 (5) and 66.0 (5)°, and between the benzene and cyclopropane rings they are 25.9 (5) and 33.9 (5)°. There are intermolecular O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds, as well as intramolecular C—H⋯O hydrogen bonds, which may be effective in stabilizing the crystal structure.
Genetic variation and evolutionary demography of the shrimp Fenneropenaeus chinensis were investigated using sequence data of the complete mitochondrial control region (CR). Fragments of 993 bp of the CR were sequenced for 93 individuals from five localities over most of the species' range in the Yellow Sea and the Bohai Sea. There were 84 variable sites defining 68 haplotypes. Haplotype diversity levels were very high (0.95 ± 0.03-0.99 ± 0.02) in F. chinensis populations, whereas those of nucleotide diversity were moderate to low (0.66 ± 0.36%-0.84 ± 0.46%). Analysis of molecular variance and conventional population statistics (FST ) revealed no significant genetic structure throughout the range of F. chinensis. Mismatch distribution, estimates of population parameters and neutrality tests revealed that the significant fluctuations and shallow coalescence of mtDNA genealogies observed were coincident with estimated demographic parameters and neutrality tests, in implying important past-population size fluctuations or range expansion. Isolation with Migration (IM) coalescence results suggest that F. chinensis, distributed along the coasts of northern China and the Korean Peninsula (about 1000 km apart), diverged recently, the estimated time-split being 12,800 (7,400-18,600) years ago.
Fenneropenaeus chinensis; mtDNA; isolation with migration (IM) coalescence; historical demography; population expansion
Peripheral chemoreflex sensitivity is potentiated in both clinical and experimental chronic heart failure (CHF). NADPH oxidase-derived superoxide mediates angiotensin II (Ang II)-enhanced carotid body (CB) chemoreceptor sensitivity in CHF rabbits, and tempol, the superoxide dismutase (SOD) mimetic, inhibits this Ang II- and CHF-enhanced superoxide anion effect. Here we investigated the role of cytoplasmic SOD [CuZn superoxide dismutase (CuZnSOD)] in the CB on chemoreceptor activity and function in CHF rabbits.
Methods and results
CuZnSOD protein expression was decreased in CBs from CHF rabbits vs. sham (P < 0.05). Adenoviral CuZnSOD (Ad CuZnSOD) gene transfer to the CBs increased CuZnSOD protein expression and significantly reduced the baseline renal sympathetic nerve activity (RSNA) and the response of RSNA to hypoxia in the CHF rabbits (P < 0.05). Single-fibre discharge from CB chemoafferents during normoxia (baseline, at ∼100 mmHg PO2) and in response to hypoxia were enhanced in CHF vs. sham rabbits (P < 0.05). Ad CuZnSOD decreased the baseline discharge (7.6 ± 1.3 vs. 12.6 ± 1.7 imp/s at ∼100 mmHg PO2) and the response to hypoxia (22.4 ± 1.6 vs. 32.3 ± 1.2 imp/s at ∼40 mmHg PO2, P < 0.05) in CHF rabbits. Ad CuZnSOD also normalized the blunted outward K+ current (IK) in CB glomus cells from CHF rabbits (369 ± 14 vs. 565 ± 31 pA/pF at +70 mV, P < 0.05). In addition, Ad CuZnSOD reduced the elevation of superoxide level in CBs from CHF rabbits.
Downregulation of CuZnSOD in the CB contributes to the enhanced activity of CB chemoreceptors and chemoreflex function in CHF rabbits.
Superoxide dismutase; Adenoviral vector; Carotid body; Sympathetic nerve activity; Chemoreceptor; Glomus cell; Chronic heart failure
A previous study from this laboratory showed that elevation of endogenous angiotensin II (Ang II) and upregulation of the angiotensin II type 1 (AT1) receptor in the carotid body (CB) are involved in the enhanced peripheral chemoreceptor sensitivity in rabbits with chronic heart failure (CHF). NADPH oxidase-derived superoxide anion mediates the effects of Ang II in many organs. We investigated whether this signaling pathway may mediate the enhanced peripheral chemoreceptor sensitivity induced by Ang II in CHF rabbits.
Methods and results:
By recording single-unit activity from the carotid sinus nerve in isolated preparations, we found that phenylarsine oxide 2 μM (PAO, NADPH oxidase inhibitor) and TEMPOL 1 mM (superoxide dismutase mimetic) significantly decreased not only the Ang II-enhanced CB chemoreceptor responses to different levels of hypoxia in sham rabbits (Δ-12.5 ± 0.8 and Δ-12.8 ± 0.9 imp/s at 40.7 ± 2.3 mm Hg of PO2, and Δ-5.6 ± 0.5 and Δ-5.3 ± 0.4 imp/s at 60.2 ± 3.1 mm Hg of PO2, p<0.05, respectively) but also the CHF-induced elevation of CB chemoreceptor responses to different levels of hypoxia (Δ-13.6 ± 1.1 and Δ-13.7 ± 0.9 imp/s at 40.9 ± 3.1 mm Hg of PO2, and Δ-6.7 ± 1.2 and Δ-6.6 ± 0.8 imp/s at 59.8 ± 3.5 mm Hg of PO2, p<0.05). In addition, mRNA and protein expressions of NADPH oxidase components (gp91phox, p40phox and p47phox) were higher in the CB from CHF rabbits compared to sham rabbits. Furthermore, 100 pM Ang II induced an increase in superoxide production in CB homogenates from sham rabbits, which was similar to that in CB homogenate from CHF rabbits. PAO and Tempol inhibited the Ang II- and CHF-enhanced superoxide anion production.
These results suggest that the enhanced peripheral chemoreceptor sensitivity mediated by Ang II in CHF rabbits occurs via a NADPH oxidase-superoxide signaling pathway.
Angiotensin; Reactive oxygen species; autonomic nervous system; chemoreceptor; heart failure
In this review, we summarize the present state of knowledge of the functional characteristics of the carotid body (CB) chemoreflex with respect to control of sympathetic nerve activity (SNA) in chronic heart failure (CHF). Evidence from both CHF patients and animal models of CHF has clearly established that the CB chemoreflex is enhanced in CHF and contributes to the tonic elevation in SNA. This adaptive change derives from altered function at the level of both the afferent and central nervous system (CNS) pathways of the reflex arc. At the level of the CB, an elevation in basal afferent discharge occurs under normoxic conditions in CHF rabbits, and the discharge responsiveness to hypoxia is enhanced. Outward voltage-gated K+ currents (IK) are suppressed in CB glomus cells from CHF rabbits, and their sensitivity to hypoxic inhibition is enhanced. These changes in IK derive partly from downregulation of nitric oxide synthase (NOS) / NO signaling and upregulation of angiotensin II (Ang II) / Ang II receptor (AT1R) signaling in glomus cells. At the level of the CNS, interactions of the enhanced input from CB chemoreceptors with altered input from baroreceptor and cardiac afferent pathways and from central Ang II further enhance sympathetic drive. In addition, impaired function of NO in the paraventricular nucleus of the hypothalamus participates in the increased SNA response to CB chemoreceptor activation. These results underscore the principle that multiple mechanisms involving Ang II and NO at the level of both the CB and CNS represent complementary and perhaps redundant adaptive mechanisms to enhance CB chemoreflex function in CHF.
Our previous study has reported that superoxide mediates ischemia-reperfusion (IR)-induced necrosis in mouse skeletal muscle. However, it remains poorly understood whether IR induces apoptosis and what factors are involved in IR-induced apoptosis in skeletal muscle. Using a murine model of tourniquet-induced hindlimb IR, we investigated the relationship between mitochondrial dysfunction and apoptosis in skeletal muscle. Hindlimbs of C57/BL6 mice were subjected to 3 h ischemia and 4 h reperfusion via placement and release of a rubber tourniquet at the greater trochanter. Compared to sham treatment, tourniquet-induced IR significantly elevated mitochondria-derived superoxide production, activated opening of mitochondrial permeability transition pore (mPTP), and caused apoptosis in the gastrocnemius muscles. Pretreatment with a superoxide dismutase mimetic (tempol, 50 mg/kg) or a mitochondrial antioxidant (co-enzyme Q10, 50 mg/kg) not only decreased mitochondria-derived superoxide production, but also inhibited mPTP opening and apoptosis in the IR gastrocnemius muscles. Additionally, an inhibitor of mPTP (cyclosporine A, 50 mg/kg) also inhibited both mPTP opening and apoptosis in the IR gastrocnemius muscles. These results suggest that mitochondria-derived superoxide overproduction triggers the mPTP opening and subsequently causes apoptosis in tourniquet-induced hindlimb IR.