Cardiovascular responses to putative chemoreceptor stimulation of embryonic common snapping turtles (Chelydra serpentina) chronically incubated in hypoxia (10% O2)

Developmental hypoxia has been shown to result in significant changes in cardiovascular development of American alligators and common snapping turtles. These include similar effects on cardiac mass and aspects of cardiovascular function. However, given the distant phylogenetic relationship between crocodilians and chelonians, we hypothesized that snapping turtles would also exhibit differences in the effects of developmental hypoxia on cardiovascular regulation. This hypothesis was based in part on prior studies that documented differences in plasticity of vagal tone on the heart between alligators and snapping turtles incubated in hypoxic conditions. To test this hypothesis, we investigated how 10% O₂ exposure over final 80% of incubation altered the heart rate and blood pressure response to two chemical manipulations of the "chemoreflex" in common snapping turtles at 70% and 90% of incubation. NaCN injections produced a dose dependent bradycardia that was mediated by cholinergic receptor stimulation. This reflex was relatively unaffected by hypoxic incubation conditions in snapping turtle embryos. Injections of the 5-HT₃ agonist phenylbiguanide (PBG) caused a pronounced bradycardia that decreased in intensity at 90% of incubation in embryos from the normoxic group while the heart rate response was unchanged in the hypoxic group. This differs from the previously reported diminished heart rate response of embryonic alligators incubated in 10% O₂, suggesting plasticity in this chemoreflex response differs between the species. Our data also indicate the cardiovascular response is mediated by a secondary cholinergic receptor stimulation however the inability of ganglionic blockade to inhibit the PBG response leaves the location of the receptors antagonized by PBG in question in embryonic snapping turtles. Primarily, our findings refute the hypothesis that hypoxic incubation decreases the "chemoreflex' response of snapping turtle embryos.

Physiologic regulation of heart rate and blood pressure involves connexin 36-containing gap junctions

Chronically elevated sympathetic nervous activity underlies many cardiovascular diseases. Elucidating the mechanisms contributing to sympathetic nervous system output may reveal new avenues of treatment. The contribution of the gap junctional protein connexin 36 (Cx36) to the regulation of sympathetic activity and thus blood pressure and heart rate was determined using a mouse with specific genetic deletion of Cx36. Ablation of the Cx36 protein was confirmed in sympathetic preganglionic neurons of Cx36-knockout (KO) mice. Telemetric analysis from conscious Cx36 KO mice revealed higher variance in heart rate and blood pressure during rest and activity compared to wild-type (WT) mice, and smaller responses to chemoreceptor activation when anesthetized. In the working heart-brain stem preparation of the Cx36-KO mouse, respiratory-coupled sympathetic nerve discharge was attenuated and responses to chemoreceptor stimulation and noxious stimulation were blunted compared to WT mice. Using whole cell patch recordings, sympathetic preganglionic neurons in spinal cord slices of Cx36-KO mice displayed lower levels of spikelet activity compared to WT mice, indicating reduced gap junction coupling between neurons. Cx36 deletion therefore disrupts normal regulation of sympathetic outflow with effects on cardiovascular parameters.-Lall, V. K., Bruce, G., Voytenko, L., Drinkhill, M., Wellershaus, K., Willecke, K., Deuchars, J., Deuchars, S. A. Physiologic regulation of heart rate and blood pressure involves connexin 36-containing gap junctions.

Novel Metabolic Abnormalities in the Tricarboxylic Acid Cycle in Peripheral Cells From Huntington's Disease Patients

Metabolic dysfunction is well-documented in Huntington's disease (HD). However, the link between the mutant huntingtin (mHTT) gene and the pathology is unknown. The tricarboxylic acid (TCA) cycle is the main metabolic pathway for the production of NADH for conversion to ATP via the electron transport chain (ETC). The objective of this study was to test for differences in enzyme activities, mRNAs and protein levels related to the TCA cycle between lymphoblasts from healthy subjects and from patients with HD. The experiments utilize the advantages of lymphoblasts to reveal new insights about HD. The large quantity of homogeneous cell populations permits multiple dynamic measures to be made on exactly comparable tissues. The activities of nine enzymes related to the TCA cycle and the expression of twenty-nine mRNAs encoding for these enzymes and enzyme complexes were measured. Cells were studied under baseline conditions and during metabolic stress. The results support our recent findings that the activities of the pyruvate dehydrogenase complex (PDHC) and succinate dehydrogenase (SDH) are elevated in HD. The data also show a large unexpected depression in MDH activities. Furthermore, message levels for isocitrate dehydrogenase 1 (IDH1) were markedly increased in in HD lymphoblasts and were responsive to treatments. The use of lymphoblasts allowed us to clarify that the reported decrease in aconitase activity in HD autopsy brains is likely due to secondary hypoxic effects. These results demonstrate the mRNA and enzymes of the TCA cycle are critical therapeutic targets that have been understudied in HD.

Memory deficits associated with sublethal cyanide poisoning relative to cyanate toxicity in rodents

Food (cassava) linamarin is metabolized into neurotoxicants cyanide and cyanate, metabolites of which we sought to elucidate the differential toxicity effects on memory. Young 6-8 weeks old male rats were treated intraperitoneally with either 2.5 mg/kg body weight (bw) cyanide (NaCN), or 50 mg/kg bw cyanate (NaOCN), or 1 μl/g bw saline, daily for 6 weeks. Short-term and long-term memories were assessed using a radial arm maze (RAM) testing paradigm. Toxic exposures had an influence on short-term working memory with fewer correct arm entries (F(2, 19) = 4.57 p < 0.05), higher working memory errors (WME) (F(2, 19) = 5.09, p < 0.05) and longer RAM navigation time (F(2, 19) = 3.91, p < 0.05) for NaOCN relative to NaCN and saline treatments. The long-term working memory was significantly impaired by cyanide with fewer correct arm entries (F(2, 19) = 7.45, p < 0.01) and increased working memory errors (F(2, 19) = 9.35 p < 0.05) in NaCN relative to NaOCN or vehicle treated animals. Reference memory was not affected by either cyanide or cyanate. Our study findings provide an experimental evidence for the biological plausibility that cassava cyanogens may induce cognition deficits. Differential patterns of memory deficits may reflect the differences in toxicity mechanisms of NaOCN relative to NaCN. Cognition deficits associated with cassava cyanogenesis may reflect a dual toxicity effect of cyanide and cyanate.

A study of cytochrome bo3 in a tethered bilayer lipid membrane

An assay has been developed in which the activity of an ubiquinol oxidase from Escherichia coli, cytochrome bo(3) (cbo(3)), is determined as a function of the hydrophobic substrate ubiquinol-10 (UQ-10) in tethered bilayer lipid membranes (tBLMs). UQ-10 was added in situ, while the enzyme activity and the UQ-10 concentration in the membrane have been determined by cyclic voltammetry. Cbo(3) is inhibited by UQ-10 at concentrations above 5-10 pmol/cm(2), while product inhibition is absent. Cyclic voltammetry has also been used to characterise the effects of three inhibitors; cyanide, inhibiting oxygen reduction; 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO), inhibiting the quinone oxidation and Zn(II), thought to block the proton channels required for oxygen reduction and proton pumping activity. The electrochemical behaviour of cbo(3) inhibited with HQNO and Zn(II) is almost identical, suggesting that Zn(II) ions inhibit the enzyme reduction by quinol, rather than oxygen reduction. This suggests that at Zn(II) concentration below 50µM the proton release of cbo(3) is inhibited, but not the proton uptake required to reduce oxygen to water.

Heme oxygenase is necessary for the excitatory response of cultured neonatal rat rostral ventrolateral medulla neurons to hypoxia

Heme oxygenase has been linked to the oxygen-sensing function of the carotid body, pulmonary vasculature, cerebral vasculature, and airway smooth muscle. We have shown previously that the cardiorespiratory regions of the rostral ventrolateral medulla are excited by local hypoxia and that heme oxygenase-2 (HO-2) is expressed in the hypoxia-chemosensitive regions of the rostral ventrolateral medulla (RVLM), the respiratory pre-Bötzinger complex, and C1 sympathoexcitatory region. To determine whether heme oxygenase is necessary for the hypoxic-excitation of dissociated RVLM neurons (P1) cultured on confluent medullary astrocytes (P5), we examined their electrophysiological responses to hypoxia (NaCN and low Po(2)) using the whole-cell perforated patch clamp technique before and after blocking heme oxygenase with tin protoporphyrin-IX (SnPP-IX). Following the electrophysiological recording, immunocytochemistry was performed on the recorded neuron to correlate the electrophysiological response to hypoxia with the expression of HO-2. We found that the responses to NaCN and hypoxia were similar. RVLM neurons responded to NaCN and low Po(2) with either depolarization or hyperpolarization and SnPP-IX blocked the depolarization response of hypoxia-excited neurons to both NaCN and low Po(2) but had no effect on the hyperpolarization response of hypoxia-depressed neurons. Consistent with this observation, HO-2 expression was present only in the hypoxia-excited neurons. We conclude that RVLM neurons are excited by hypoxia via a heme oxygenase-dependent mechanism.

Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.

Isoflurane attenuates myoglobin release during ischemic and/or reperfusion periods

BACKGROUND

Recently, we have developed cardiac microdialysis for detection of protein leakage from the injured myocardium. We examined whether the exposures to isoflurane would exert a beneficial effect on myocardial injury caused by ischemia or reperfusion.

METHODS

A dialysis probe was implanted into the left ventricle free wall in the rabbits. The dialysate myoglobin level served as an index of myocardial interstitial myoglobin levels. Rabbits were randomly assigned to one of three groups: (1) without exposure to isoflurane (vehicle, n=6), (2) inhale 1 MAC isoflurane once for 30 min (ISO30-1, n=6), and (3) twice for 30 min (ISO30-2, n=6). All rabbits underwent 30 min of coronary occlusion and 60 min of reperfusion. To determine whether the isoflurane induced myocardial protection against chemical hypoxia, sodium cyanide (30 mM) was administered and dialysate myoglobin levels were measured with (n=6) and without pre-exposure to isoflurane twice for 30 min (n=6).

RESULTS

In all three groups dialysate myoglobin levels were increased by coronary occlusion and furthermore augmented by reperfusion. In comparison with the vehicle group, the ISO30-1 group suppressed only the increase in the dialysate myoglobin level during reperfusion. The ISO30-2 group suppressed during both the ischemic and reperfusion periods. Cyanide induced increases in dialysate myoglobin levels. These increments in dialysate myoglobin levels were suppressed by repeated exposure to isoflurane.

CONCLUSION

Repeated exposure to isoflurane suppressed myocardial myoglobin release caused by both ischemia and reperfusion injury. Isoflurane may provide protection against myocardial ischemia/reperfusion and hypoxic injuries.

Ethylene controls autophosphorylation of the histidine kinase domain in ethylene receptor ETR1

Perception of the phytohormone ethylene is accomplished by a small family of integral membrane receptors. In Arabidopsis, five ethylene receptor proteins are known, including ethylene resistant 1 (ETR1). The hydrophobic amino-terminal domain of these receptors contains the ethylene-binding site while the carboxyl-terminal part consists of a histidine kinase domain and a response regulator domain, which are well known elements found in bacterial two-component signaling. The soluble membrane-extrinsic carboxyl-terminal part of the receptor, which is likely to play an important role in signal transduction, showed intrinsic kinase activity when expressed and purified on its own. However, a correlation between signal input and autokinase activity was not established in these studies, as receptors were missing the transmembrane amino-terminal sensor domain. Thus, it is still unclear whether autophosphorylation occurs in response to perception of the ethylene signal. Here, we report on autophosphorylation studies of purified full-length ETR1. Autokinase activity of the purified receptor is controlled by ethylene or by ethylene agonists like the pi-acceptor compound cyanide. In fact, both signal molecules were able to completely turn off the intrinsic kinase activity. Furthermore, the observed inhibition of autophosphorylation in ETR1 by both molecules could be prevented when the ethylene antagonist 1-methyl-cyclopropene (MCP) was applied.

Gill chemoreceptors and cardio-respiratory reflexes in the neotropical teleost pacu, Piaractus mesopotamicus

This study examined the location and distribution of O(2) chemoreceptors involved in cardio-respiratory responses to hypoxia in the neotropical teleost, the pacu (Piaractus mesopotamicus). Intact fish and fish experiencing progressive gill denervation by selective transection of cranial nerves IX and X were exposed to gradual hypoxia and submitted to intrabuccal and intravenous injections of NaCN while their heart rate, ventilation rate and ventilation amplitude were measured. The chemoreceptors producing reflex bradycardia were confined to, but distributed along all gill arches, and were sensitive to O(2) levels in the water and the blood. Ventilatory responses to all stimuli, though modified, continued following gill denervation, however, indicating the presence of internally and externally oriented receptors along all gill arches and either in the pseudobranch or at extra-branchial sites. Chemoreceptors located on the first pair of gill arches and innervated by the glossopharyngeal nerve appeared to attenuate the cardiac and respiratory responses to hypoxia. The data indicate that the location and distribution of cardio-respiratory O(2) receptors are not identical to those in tambaqui (Colossoma macropomum) despite their similar habitats and close phylogenetic lineage, although the differences between the two species could reduce to nothing more than the presence or absence of the pseudobranch.

Is urea pulsing in toadfish related to environmental O2 or CO2 levels?

The neurochemical, serotonin (5-hydroxytryptamine; 5-HT) is involved in the regulation of toadfish pulsatile urea excretion as well as the teleost hypoxia response. Thus, the goal of this study was to determine whether environmental conditions that activate branchial chemoreceptors also trigger pulsatile urea excretion in toadfish, since environmental dissolved oxygen levels in a typical toadfish habitat show significant diel fluctuations, often reaching hypoxic conditions at dawn. Toadfish were fitted with arterial, venous and/or buccal catheters and were exposed to various environmental conditions, and/or injected with the O(2) chemoreceptor agonist NaCN or the 5-HT(2) receptor agonist alpha-methyl-5HT. Arterial PO(2), as well as ammonia and urea excretion were monitored. Natural fluctuations in arterial PO(2) levels in toadfish did not correlate with the occurrence of a urea pulse. Chronic exposure (24 h) of toadfish to hyperoxia was without effect on nitrogen excretion, however, exposure to hypoxia caused a significant reduction in the frequency of urea pulses, and exposure to hypercapnia resulted in a reduction in the percentage of nitrogen waste excreted as urea. Of toadfish exposed acutely to hypoxia, 20% pulsed within 1 h, whereas none pulsed after normoxic or hypercapnic treatments. Furthermore, 20% of fish injected intravenously with NaCN pulsed within 1 h of injection, but no fish pulsed after injection of NaCN into the buccal cavity. To test whether environmental conditions affected 5-HT(2) receptors, toadfish were injected with alpha-methyl-5HT, which elicits urea pulses in toadfish. No significant differences in pulse size occurred among the various environmental treatments. Our findings suggest that neither the environmental conditions of hypoxia, hyperoxia or hypercapnia, nor direct branchial chemoreceptor activation by NaCN play a major role in the regulation of pulsatile urea excretion in toadfish.

Evidence of ROS generation by mitochondria in cells with impaired electron transport chain and mitochondrial DNA damage

Mitochondrial damage is a well known cause of mitochondria-related diseases. A major mechanism underlying the development of mitochondria-related diseases is thought to be an increase in intracellular oxidative stress produced by impairment of the mitochondrial electron transport chain (ETC). However, clear evidence of intracellular free radical generation has not been clearly provided for mitochondrial DNA (mtDNA)-damaged cells. In this study, using the novel fluorescence dye, 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (HPF), which was designed to detect hydroxyl radicals (*OH), intracellular free radical formation was examined in 143B cells (parental cells), 143B-rho(0) cells (mtDNA-lacking cells), 87 wt (cybrid), and cybrids of 4977-bp mtDNA deletion (common deletion) cells containing the deletion with 0%, 5%, 50% and >99% frequency (HeLacot, BH5, BH50 and BH3.12, respectively), using a laser confocal microscope detection method. ETC inhibitors (rotenone, 3-nitropropionic acid, thenoyltrifluoroacetone, antimycin A and sodium cyanide) were also tested to determine whether inhibitor treatment increased intracellular reactive oxygen species (ROS) generation. A significant increase in ROS for 143B-rho(0) cells was observed compared with 143B cells. However, for the 87 wt cybrid, no increase was observed. An increase was also observed in the mtDNA-deleted cells BH50 and BH3.12. The ETC inhibitors increased intracellular ROS in both 143B and 143B-rho(0) cells. Furthermore, in every fluorescence image, the fluorescence dye appeared localized around the nuclei. To clarify the localization, we double-stained cells with the dye and MitoTracker Red. The resulting fluorescence was consistently located in mitochondria. Furthermore, manganese superoxide dismutase (MnSOD) cDNA-transfected cells had decreased ROS. These results suggest that more ROS are generated from mitochondria in ETC-inhibited and mtDNA-damaged cells, which have impaired ETC.

Arachidonic acid enhances intracellular [Ca2+]i increase and mitochondrial depolarization induced by glutamate in cerebellar granule cells

Maturation of primary neuronal cultures is accompanied by an increase in the proportion of cells that exhibit biphasic increase in free cytoplasmic Ca2+ ([Ca2+]i) followed by synchronic decrease in electrical potential difference across the inner mitochondrial membrane (DeltaPsim) in response to stimulation of glutamate receptors. In the present study we have examined whether the appearance of the second phase of [Ca2+]i change can be attributed to arachidonic acid (AA) release in response to the effect of glutamate (Glu) on neurons. Using primary culture of rat cerebellar granule cells we have investigated the effect of AA (1-20 microM) on [Ca2+]i, DeltaPsim, and [ATP] and changes in these parameters induced by neurotoxic concentrations of Glu (100 microM, 10-40 min). At =10 microM, AA caused insignificant decrease in DeltaPsim without any influence on [Ca2+]i. The mitochondrial ATPase inhibitor oligomycin enhanced AA-induced decrease in DeltaPsim; this suggests that AA may inhibit mitochondrial respiration. Addition of AA during the treatment with Glu resulted in more pronounced augmentation of [Ca2+]i and the decrease in DeltaPsim than the changes in these parameters observed during independent action of AA; removal of Glu did not abolish these changes. An inhibitor of the cyclooxygenase and lipoxygenase pathways of AA metabolism, 5,8,11,14-eicosatetraynoic acid, increased the proportion of neurons characterized by Glu-induced biphasic increase in [Ca2+]i and the decrease in DeltaPsim. Palmitic acid (30 microM) did not increase the percentage of neurons exhibiting biphasic response to Glu. Co-administration of AA and Glu caused 2-3 times more pronounced decrease in ATP concentrations than that observed during the independent effect of AA and Glu. The data suggest that AA may influence the functional state of mitochondria, and these changes may promote biphasic [Ca2+]i and DeltaPsim responses of neurons to the neurotoxic effect of Glu.

Loss of nitric oxide-mediated down-regulation of NMDA receptors in neurofilament aggregate-bearing motor neurons in vitro: implications for motor neuron disease

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder in which excitotoxicity has been implicated as a cause for cell death. To examine neurofilament (NF) aggregate-mediated sensitization of motor neurons to NMDA excitotoxicity, we examined NMDA receptor expression and the impact of NO donors (NOC12 or NOC5) or sodium cyanide (NaCN) on calcium influx and viability in dissociated motor neurons derived from wt and hNFL+/+ (NF aggregate-forming) mice. Alterations in intracellular calcium were assayed using Oregon Green calcium dye and the extent of apoptosis using active caspase-3 immunoreactivity. Although NF aggregate-bearing neurons demonstrated increased intracellular calcium levels and enhanced cell death in response to NMDA receptor activation, this was not associated with increased NMDA receptor expression. The down-regulation of the NMDA receptor using NO donors decreased calcium influx and caspase-3 activation in aggregate-bearing neurons, but had no effect on wt cultures. The converse was observed with NaCN in which intracellular calcium levels increased significantly in wt cultures in association with increased cell death. No effect was observed in aggregate-bearing neurons. These findings suggest that the presence of NF aggregates renders motor neurons more susceptible to NMDA-mediated excitotoxicity, and that this can be reversed by NO.

Expression of histamine receptors and effect of histamine in the rat carotid body chemoafferent pathway

Chemosensory information from peripheral arterial oxygen sensors in the carotid body is relayed by petrosal ganglion neurons to the respiratory networks in the medulla oblongata. Biogenic amines, including histamine, released from glomus (type I) cells of the carotid body are considered to be primary transmitters in hypoxic chemosensitivity. Immunocytochemistry at light-and electron-microscopical levels, and RT-PCR, revealed the expression of histamine receptors 1 and 3 as well as histidine decarboxylase in the rat carotid body glomus cells and petrosal ganglion neurons. Histamine receptors 1 and 3, but not histidine decarboxylase, were also observed in the ventrolateral, intermediate and commissural subnuclei of the nucleus tractus solitarii in the medulla oblongata. In order to examine the possible role of histamine in the afferent branch of the respiratory system, we applied histamine receptor 1 and 3 agonists to the carotid body, which caused a mildly increased phrenic nerve activity in a working heart-brainstem preparation. Moreover, microinjection of antagonists of histamine receptors 1 and 3 into the nucleus tractus solitarii caused significant changes in the inspiratory timing and the chemoreceptor response. Our data show that histamine acting via histamine receptors 1 and 3 plays an important neuromodulatory role in the afferent control of chemosensitivity.

Effects of intermittent hypoxia on cat petrosal ganglion responses induced by acetylcholine, adenosine 5'-triphosphate and NaCN

Exposure to chronic intermittent hypoxia (CIH) for 4 days enhances the cat carotid body (CB) chemosensory responses to acute hypoxia. However, it is not known if CIH enhances the responses of the petrosal ganglion (PG) neurons that innervate the CB chemoreceptor cells. Accordingly, we studied the effects of the CB putative excitatory transmitter acetylcholine (ACh) and adenosine 5 -triphosphate (ATP), and the effects of citotoxic hypoxia (NaCN) applied to the isolated PG from cats exposed to CIH for 4 days. The dose-dependent curve parameters of the frequency of discharges evoked in the carotid sinus nerve by the application of ACh, ATP and NaCN to the isolated PG in control condition were not significantly modified in the CIH-treated cats. Present results suggest that CIH enhances the chemosensory responses to acute hypoxia acting primarily at the chemoreceptor cells, without major changes in the response of PG neurons evoked by the application of putative CB excitatory transmitters to their somata.

Are the carotid bodies of the guinea-pig functional?

We have previously observed that the guinea-pig appears to have a relatively poor ventilatory (V (E)) response to hypoxia, compared to other mammals. Therefore, in this study, we questioned the ability of the carotid bodies (primary peripheral chemoreceptors) in the guinea-pig to detect hypoxia. The ventilatory responses to poikilocapnic hypoxia (8% O(2)), poikilooxic hypercapnia (8% CO(2)), hyperoxia (100% O(2)) and cyanide (NaCN - 200 mug/kg, i.v.) were assessed before and after carotid body denervation (CBD) in anaesthetized guinea-pigs. Although CBD attenuated the V (E) responses to hypercapnia and cyanide, it had no effect on normoxic breathing or the V (E) responses to hypoxia or hyperoxia. In a separate group of guinea-pigs, nerve activity was recorded from single or few-fibre preparations of the carotid sinus nerve (CSN). Basal chemoreceptor activity could not be detected from any of the nerve preparations. NaCN and hypercapnia consistently provoked an increase in neural activity. In contrast, hypoxia never clearly increased activity in any of the single or few-fibre preparations isolated from the CSN. In conclusion, although the carotid bodies of the guinea-pig, like those of other mammals, are able to detect hypercapnia and histotoxic hypoxia and elicit a reflex increase in V (E), they are essentially hypoxia-insensitive. The latter may explain, at least in part, the relatively poor V (E) response to hypoxia shown by the guinea-pig.

[The mechanism of ABA-induced apoplastic H2O2 accumulation in maize leaves]

In maize (Zea mays L.) cells, the sources of apoplast hydrogen peroxide (H(2)O(2)) induced by abscisic acid (ABA) has been proposed. Histochemical and cytochemical localization of ABA-induced H(2)O(2) production in leaves of maize was examined, using 3, 3-diaminobenzidine (DAB) and cerium chloride (CeCl(3)) staining respectively. Pretreatment with two different inhibitors for each enzymes, with diphenylene iodonium (DPI) and imidazole against NADPH oxidase, NaCN and NaN(3) against peroxidases (POD), and quinacrine and guazatine against polyamine oxidases (PAO), reduced H(2)O(2) accumulation induced by ABA. Among them, NADPH oxidase inhibitors arrested the production of apoplastic H(2)O(2) most strongly (Figs.1,2). Further studies showed that exogenous ABA treatment could enhance the activities of plasma membrane (PM) NADPH oxidase, cell wall POD and apoplast PAO significantly. Moreover, the activity of PM NADPH oxidase kept increasing before 1.5 h, while the other two enzymes began to decrease at 0.5 h within 2 h by ABA treatment (Fig.3). The results suggest that exogenous ABA treatment can lead to significant increases in H(2)O(2) accumulation in apoplast through up-regulating the activities of the PM NADPH oxidases, cell wall POD and apoplast PAO, of which the first one plays a central role in ABA-induced apoplastic H(2)O(2) accumulation.

Different states of energy metabolism in the vertebrate retina can be identified by stimulus-related changes in near UV transmission

BACKGROUND

Our aim was to identify different states of energy metabolism in the perfused isolated vertebrate retina by simultaneous recordings of light-evoked changes of transretinal potential (TRP) and spectroscopic changes related to oxidation of pyridine nucleotides.

METHODS

Isolated retinas were obtained from R.esc. and superfused. For each setting, three experiments were performed. Eighteen retinas were used. TRP as a response to light stimulation was recorded simultaneously with stimulus-induced transmission shift at 350 nm. These responses were recorded under normal conditions, under withdrawal of oxygen and glucose, and after addition of electron transport inhibitors and uncouplers of oxidative phosphorylation.

RESULTS

Under normal conditions, TRP was strongly correlated with transmission shift after light stimulation. Without oxygen, amplitudes of stimulus-related TRP decreased and response related increase of transmission at 350 nm was reduced. The retina showed a much higher general absorption of the analyzing light. During glucose lack, an overall increase in transmission at 350 nm could be observed. The addition of Amytal yielded a specific reduction of the OFF components. Cyanide attenuated the ON and OFF components. Dinitrophenol yielded a considerable loss of the electrical ON response. Transmission change was affected less than electrical signal. Chlorophenylhydrazine induced a reproducible reduction of electrical responses, with a relative increase of transmission shift at 350 nm.

CONCLUSION

In the isolated perfused retina, different states of energy metabolism and their specific impact on neuroretinal responses can be examined by simultaneous recordings of stimulus-related neuronal activity and spectroscopic changes.

Arginine-vasopressin mediates central and peripheral glucose regulation in response to carotid body receptor stimulation with Na-cyanide

Hypoxic stimulation of the carotid body receptors (CBR) results in a rapid hyperglycemia with an increase in brain glucose retention. Previous work indicates that neurohypophysectomy inhibits this hyperglycemic response. Here, we show that systemic arginine vasopressin (AVP) induced a transient, but significant, increase in blood glucose levels and increased brain glucose retention, a response similar to that observed after CBR stimulation. Comparable results were obtained after intracerebral infusion of AVP. Systemic AVP-induced changes were maintained in hypophysectomized rats but were not observed after adrenalectomy. Glycemic changes after CBR stimulation were inhibited by pharmacological blockage of AVP V1a receptors with a V1a-selective receptor antagonist ([β-Mercapto-β,β-cyclopentamethylenepropionyl1,O-me-Tyr2, Arg8]-vasopressin). Importantly, local application of micro-doses of this antagonist to the liver was sufficient to abolish the hyperglycemic response after CBR stimulation. These results suggest that AVP is a mediator of the hyperglycemic reflex and cerebral glucose retention following CBR stimulation. We propose that hepatic activation of AVP V1a receptors is essential for this hyperglycemic response.

Metabolic regulation of neutrophil spreading, membrane tubulovesicular extensions (cytonemes) formation and intracellular pH upon adhesion to fibronectin

Circulating leukocytes have a round cell shape and roll along vessel walls. However, metabolic disorders can lead them to adhere to the endothelium and spread (flatten). We studied the metabolic regulation of adhesion, spreading and intracellular pH (pHi) of neutrophils (polymorphonuclear leukocytes) upon adhesion to fibronectin-coated substrata. Resting neutrophils adhered and spread on fibronectin. An increase in pHi accompanied neutrophil spreading. Inhibition of oxidative phosphorylation or inhibition of P- and F-type ATPases affected neither neutrophil spreading nor pHi. Inhibition of glucose metabolism or V-ATPase impaired neutrophil spreading, blocked the increase in the pHi and induced extrusion of membrane tubulovesicular extensions (cytonemes), anchoring cells to substrata. Omission of extracellular Na(+) and inhibition of chloride channels caused a similar effect. We propose that these tubulovesicular extensions represent protrusions of exocytotic trafficking, supplying the plasma membrane of neutrophils with ion exchange mechanisms and additional membrane for spreading. Glucose metabolism and V-type ATPase could affect fusion of exocytotic trafficking with the plasma membrane, thus controlling neutrophil adhesive state and pHi. Cl(-) efflux through chloride channels and Na(+) influx seem to be involved in the regulation of the V-ATPase by carrying out charge compensation for the proton-pumping activity and through V-ATPase in regulation of neutrophil spreading and pHi.

Limited oxygen diffusion accelerates fatigue development in mouse skeletal muscle

Isolated whole skeletal muscles fatigue more rapidly than isolated single muscle fibres. We have now employed this difference to study mechanisms of skeletal muscle fatigue. Isolated whole soleus and extensor digitorum longus (EDL) muscles were fatigued by repeated tetanic stimulation while measuring force production. Neither application of 10 mm lactic acid nor increasing the [K(+)] of the bath solution from 5 to 10 mm had any significant effect on the rate of force decline during fatigue induced by repeated brief tetani. Soleus muscles fatigued slightly faster during continuous tetanic stimulation in 10 mm[K(+)]. Inhibition of mitochondrial respiration with cyanide resulted in a faster fatigue development in both soleus and EDL muscles. Single soleus muscle fibres were fatigued by repeated tetani while measuring force and myoplasmic free [Ca(2+)] ([Ca(2+)](i)). Under control conditions, the single fibres were substantially more fatigue resistant than the whole soleus muscles; tetanic force at the end of a series of 100 tetani was reduced by about 10% and 50%, respectively. However, in the presence of cyanide, fatigue developed at a similar rate in whole muscles and single fibres, and tetanic force at the end of fatiguing stimulation was reduced by approximately 80%. The force decrease in the presence of cyanide was associated with a approximately 50% decrease in tetanic [Ca(2+)](i), compared with an increase of approximately 20% without cyanide. In conclusion, lactic acid or [K(+)] has little impact on fatigue induced by repeated tetani, whereas hypoxia speeds up fatigue development and this is mainly due to an impaired Ca(2+) release from the sarcoplasmic reticulum.

Peripheral chemoreceptor inputs to retrotrapezoid nucleus (RTN) CO2-sensitive neurons in rats

The rat retrotrapezoid nucleus (RTN) contains pH-sensitive neurons that are putative central chemoreceptors. Here, we examined whether these neurons respond to peripheral chemoreceptor stimulation and whether the input is direct from the solitary tract nucleus (NTS) or indirect via the respiratory network. A dense neuronal projection from commissural NTS (commNTS) to RTN was revealed using the anterograde tracer biotinylated dextran amine (BDA). Within RTN, 51% of BDA-labelled axonal varicosities contained detectable levels of vesicular glutamate transporter-2 (VGLUT2) but only 5% contained glutamic acid decarboxylase-67 (GAD67). Awake rats were exposed to hypoxia (n = 6) or normoxia (n = 5) 1 week after injection of the retrograde tracer cholera toxin B (CTB) into RTN. Hypoxia-activated neurons were identified by the presence of Fos-immunoreactive nuclei. CommNTS neurons immunoreactive for both Fos and CTB were found only in hypoxia-treated rats. VGLUT2 mRNA was detected in 92 +/- 13% of these neurons whereas only 12 +/- 9% contained GAD67 mRNA. In urethane-chloralose-anaesthetized rats, bilateral inhibition of the RTN with muscimol eliminated the phrenic nerve discharge (PND) at rest, during hyperoxic hypercapnia (10% CO(2)), and during peripheral chemoreceptor stimulation (hypoxia and/or i.v. sodium cyanide, NaCN). RTN CO(2)-activated neurons were recorded extracellularly in anaesthetized intact or vagotomized rats. These neurons were strongly activated by hypoxia (10-15% O(2); 30 s) or by NaCN. Hypoxia and NaCN were ineffective in rats with carotid chemoreceptor denervation. Bilateral injection of muscimol into the ventral respiratory column 1.5 mm caudal to RTN eliminated PND and the respiratory modulation of RTN neurons. Muscimol did not change the threshold and sensitivity of RTN neurons to hyperoxic hypercapnia nor their activation by peripheral chemoreceptor stimulation. In conclusion, RTN neurons respond to brain P(CO(2)) presumably via their intrinsic chemosensitivity and to carotid chemoreceptor activation via a direct glutamatergic pathway from commNTS that bypasses the respiratory network. RTN neurons probably contribute a portion of the chemical drive to breathe.

Statins inhibit hypoxia-induced endothelial proliferation by preventing calcium-induced ROS formation

Pathological hypoxia plays an important role in many diseases, such as atherosclerosis, cancer, and rheumatoid arthritis. The aim of the present study was to examine the effects of different statins on hypoxia-induced endothelial cell signalling. Human umbilical cord vein endothelial cells (HUVEC) were treated with NaCN (CN, 2.5 mmol/l) to simulate a transient hypoxia. The CN-induced increase of endothelial cell numbers was significantly (n = 10, p < 0.01) reduced by the Ca(2+) chelator BAPTA (10 micromol/l), or the reactive oxygen species (ROS) scavenger N-acetylcysteine (ACC, 1 mmol/l), or the NAD(P)H-oxidase inhibitor diphenyleneiodonium (DPI, 5 micromol/l). In detail, cell numbers were (in percentage of control): 163.24 (CN), 90.06 (CN+ACC), 92.06 (CN+DPI). Intracellular-Ca(2+) and -ROS, analysed by fluorescence imaging, were significantly increased by CN. Interestingly, the CN-induced increase of ROS was in part Ca(2+)-dependent, whereas the Ca(2+) increase was not ROS-dependent. Simvastatin (5 micromol/l), fluvastatin (2.5 micromol/l), and cerivastatin (0.1 micromol/l) all reduced CN-induced proliferation, ROS generation and Ca(2+) increase. Cell viability was not reduced by the statins and the antiproliferative effect was completely reversed by mevalonate (500 micromol/l). In conclusion our study demonstrates that statins block hypoxia-associated endothelial proliferation by preventing the increase of Ca(2+) and ROS.

Effects of Silica on Mitochondrial Functions of the Proximal Tubule Cells in Rats

AIM

Despite the belief that silica (Si) is an inert and non-toxic ingredient, latest studies indicated that it is a potent mitochondria activator and Si-induced ROS generation is involved in the inflammatory reactions of silicotic lungs. Si cytotoxicity has been well studied in phagocytic cells, but its effects on the mitochondria of proximal tubule cells which are continuously exposed to filtered blood-borne soluble Si were not known.

METHODS

Using renal cortical slices and isolated mitochondria, the effect of high dietary Si on the mitochondrial functions of proximal tubule cells was studied in rats exposed to 50 mg/kg sodium metasilicate-containing water for 8 days.

RESULTS

Digested Si did not accumulate in kidney cortex, it was totally eliminated in the urine. Glomerular filtration rate as well as urine output were normal. Despite unaltered blood and cortex Si levels, ammonia production of cortical slices and isolated mitochondria was increased significantly and this was further increased by L-NAME pre-treatment. Elevated mitochondrial oxygen utilization was associated with increased ammonia production. Cyclosporin-A-sensitive mtPTP increase was associated with unchanged K(ATP) channels in the mitochondria of Si-exposed rats.

CONCLUSION

These results suggested that dietary Si increases both extracellular and intracellular ammoniagenesis by elevating mitochondrial oxygen utilisation.

Reduced effectiveness of HMR 1098 in blocking cardiac sarcolemmal K(ATP) channels during metabolic stress

ATP-sensitive K(+) (K(ATP)) channels are involved in ischemic cardioprotection induced by preconditioning (IPC), though the relative role of sarcolemmal (sK(ATP)) and mitochondrial (mitoK(ATP)) channels remains controversial. The sK(ATP)-selective sulphonylthiourea HMR 1098 has often been reported to be without effect on ischemic cardioprotection, suggesting minimal involvement of sK(ATP). Since some sulphonylureas show reduced potency under conditions of metabolic stress, we used patch clamp to assess the ability of HMR 1098 to block sK(ATP) currents of adult rat ventricular myocytes activated by metabolic inhibition (MI, NaCN+iodoacetate). In contrast to the prototype sulphonylurea glibenclamide, HMR 1098 (10 muM) was without effect on sK(ATP) currents, and also did not inhibit MI-induced action potential shortening. However, HMR 1098 blocked sK(ATP) current induced by the K(ATP) opener pinacidil (IC(50)=0.36+/-0.02 muM), and reversed pinacidil-induced action potential shortening. In inside-out patches, block by HMR 1098 was relieved by increasing MgADP concentrations (1-100 muM). HMR 1098 inhibited pinacidil-activated recombinant Kir6.2/SUR2A channels with a similar IC(50) (0.30+/-0.04 muM), but was less effective when channels were activated by low intracellular ATP. HMR 1098 displaced binding of the pinacidil analogue [(3)H]P1075 to native cardiac membranes with a biphasic inhibition curve. Our results show that HMR 1098 becomes a much less effective inhibitor of sK(ATP) during metabolic stress, and suggest that the lack of effect of HMR 1098 on ischemic cardioprotection reported in some studies may represent loss of block by the drug under these conditions rather than a lack of involvement of sK(ATP) channels.

Effects of carotid body excision on recovery of respiratory function in C2 hemisected adult rats

In a previous study, we described the spontaneous recovery of respiratory motor function in adult rats subjected to a left C2 hemisection 6-16 weeks post-injury without any therapeutic intervention. We extend the previous findings by demonstrating in the present study that rats subjected to a left C2 hemisection with bilateral carotid body excision will also recover respiratory-related activity in the paralyzed ipsilateral hemidiaphragm. However, in this instance, recovery is significantly accelerated; i.e., it is evident as early as 2 weeks after spinal cord injury. Two experimental groups (and noninjured and sham-operated controls) of rats were employed in the study. H-CBE animals were subjected to a left C2 hemisection plus bilateral carotid body excision while H-CBI animals were subjected to a left C2 hemisection only. Carotid body excision was confirmed by the sodium cyanide test. The animals were allowed to survive for 2 weeks after hemisection. Thereafter, electrophysiologic assessment of respiratory activity was conducted in all animals. Spontaneous recovery of respiratory-related activity in the paralyzed hemidiaphragm (indicated by left phrenic nerve activity) was detected in all H-CBE animals while H-CBI animals did not express spontaneous recovery of diaphragmatic activity. The magnitude of recovered activity when expressed as a function of contralateral phrenic nerve activity was 48.8 +/- 3.8%. When expressed as a function of the homolateral phrenic nerve in noninjured animals, the magnitude amounted to 25.6 +/- 2.8%. Although the mechanisms responsible for the apparent early onset of spontaneous recovery are unknown, it is likely that a reorganization of the respiratory circuitry in the CNS may be involved. The significance of the findings is that it may be feasible to modulate the onset of functional recovery following cervical spinal cord injury by specifically targeting peripheral chemoreceptors.

Characterization of tetraethylammonium uptake across the basolateral membrane of theDrosophilaMalpighian (renal) tubule

Basolateral transport of the prototypical type I organic cation tetraethylammonium (TEA) by the Malpighian tubules of Drosophila melanogaster was studied using measurements of basolateral membrane potential (Vbl) and uptake of [14C]-labeled TEA. TEA uptake was metabolically dependent and saturable (maximal rate of mediated TEA uptake by all potential transport processes, reflecting the total transport capacity of the membrane, 0.87 pmol·tubule−1·min−1; concentration of TEA at 0.5 of the maximal rate of TEA uptake value, 24 μM). TEA uptake in Malpighian tubules was inhibited by a number of type I (e.g., cimetidine, quinine, and TEA) and type II (e.g., verapamil) organic cations and was dependent on Vbl. TEA uptake was reduced in response to conditions that depolarized Vbl(high-K+saline, Na+-free saline, NaCN) and increased in conditions that hyperpolarized Vbl(low-K+saline). Addition of TEA to the saline bathing Malpighian tubules rapidly depolarized the Vbl, indicating that TEA uptake was electrogenic. Blockade of K+channels with Ba2+did not block effects of TEA on Vblor TEA uptake indicating that TEA uptake does not occur through K+channels. This is the first study to provide physiological evidence for an electrogenic carrier-mediated basolateral organic cation transport mechanism in insect Malpighian tubules. Our results also suggest that the mechanism of basolateral TEA uptake by Malpighian tubules is distinct from that found in vertebrate renal tubules.

Microdialysis separately monitors myocardial interstitial myoglobin during ischemia and reperfusion

Direct monitoring of myoglobin efflux during ischemia and reperfusion has been limited because of inherent sample collection problems in the ischemic region. Recently, the cardiac dialysis technique has offered a powerful method for monitoring myocardial interstitial levels of low-molecular-weight compounds in the cardiac ischemic region. In the present study, we extended the molecular target to high-molecular-weight compounds by use of microdialysis probes with a high-molecular-mass cutoff and monitored myocardial interstitial myoglobin levels. A dialysis probe was implanted in the left ventricular free wall in anesthetized rabbits. The main coronary artery was occluded for 60 or 120 min. We examined the effects of myocardial ischemia and reperfusion on myocardial interstitial myoglobin levels. Interstitial myoglobin increased within 15 min of ischemia and continued to increase during 120 min of ischemia, whereas blood myoglobin increased at 45 min of ischemia. Lactate and myoglobin in the interstitial space increased during the same period. At 60 min of ischemia, reperfusion markedly accelerated interstitial myoglobin release. The interstitial myoglobin level was fivefold higher at 0–15 min of reperfusion than at 60–75 min of coronary occlusion. The dialysis technique permits earlier detection of myoglobin release and separately monitors myoglobin release during ischemia and reperfusion. Myocardial interstitial myoglobin levels can serve as an index of myocardial injury evoked by ischemia or reperfusion.

Hypoxia/reoxygenation reduces microvascular endothelial cell coupling by a tyrosine and MAP kinase dependent pathway

Communication of electrical signals along the microvascular endothelium plays a key role in integrating microvascular function required for local regulation of blood flow. The aim of the present study was to examine the effect of a short-term hypoxia (0.1% O(2), 1 h) plus reoxygenation (H/R) on electrical coupling in cultured monolayers of microvascular endothelial cells (rat skeletal muscle origin). To assess coupling, we used a current injection technique and a Bessel function model to compute the intercellular resistance (an inverse measure of coupling) and cell membrane resistivity (a measure of resistance to current leakage across the cell membrane). H/R resulted in rapid (within 4 min after reoxygenation) and sustained (up to 100 min) reduction in intercellular coupling, but it did not alter membrane resistivity. H/R did not alter gap junction protein connexin 43 expression nor its tyrosine phosphorylation as determined by immunoblot and immunoprecipitation analyses. Inhibition of mitochondrial respiration (1 mM NaCN) did not mimic the effect of H/R. However, pre-treatment of monolayers with tyrphostin A48 (1.5 microM), PP2 (10 nM) (tyrosine kinase inhibitors), U 0126 (20 microM), and PD 98059 (5 microM) (MEK1/2 inhibitors) inhibited the H/R-induced reduction in coupling. These results indicate that endothelial cell coupling was reduced quickly after reoxygenation, via activation of a tyrosine and MAP kinase dependent pathway. We predict that a short-term H/R can rapidly compromise microvascular function in terms of reduced cellular communication along the vascular wall.

Ovalbumin sensitization alters the ventilatory responses to chemical challenges in guinea pigs

Patients with chronic bronchial asthma show a depressed ventilatory response to hypoxia (DVH), but the underlying mechanism remains unclear. We tested whether DVH existed in ovalbumin (Ova)-treated guinea pigs, an established animal model of asthma. Twelve guinea pigs were exposed to Ova (1% in saline) or saline aerosol (control) for 5 min, 5 days/wk, for 2 wk. After completing aerosol exposure, the animals were anesthetized and exposed to systemic hypoxia. Ova treatment had no effects on animal body weight, baseline cardiorespiratory variables, or arterial blood O2 and CO2 tensions, but it attenuated the ventilatory response to hypoxia (10 breaths of pure N2) by 65% (P < 0.05). When the animals were subjected to intracarotid injections of sodium cyanide (20 microg) and doxapram (2 mg) to selectively stimulate carotid chemoreceptors, the ventilatory responses were reduced by 50% (P < 0.05) and 74% (P < 0.05), respectively. In contrast, Ova exposure failed to affect the ventilatory response to CO2 (7% CO2-21% O2-balance N2 for 5 min; P > 0.05). Furthermore, the apneic response evoked by stimulating bronchopulmonary C fibers (PCFs) with right atrial injection of capsaicin (5 microg) was markedly increased in the Ova-sensitized group (5.02 +/- 1.56 s), compared with the control group (1.82 +/- 0.45 s; P < 0.05). These results suggest that Ova sensitization induces a DVH in guinea pigs, which probably results from an attenuation of the carotid chemoreceptor-mediated ventilatory excitation and an enhancement of the PCF-mediated ventilatory inhibition.

Oxidative phosphorylation and the tricarboxylic acid cycle are essential for normal development of mouse ovarian follicles

BACKGROUND

Mouse ovarian follicles are typically grown in upright drops of culture medium. Recently we found that culture of follicles at the medium-gas interface in inverted drops markedly improved follicular development, possibly due to improved access of oxygen to the follicle. In this study, we examined the importance of aerobic energy metabolism for follicle development by culturing mouse follicles (198 6 16.5 initial microm diameter, mean 6 SD) in the presence of phosphorylation and tricarboxylic acid (TCA) cycle inhibitors.

METHODS

All inhibitors were tested in the inverted system using 100 microl medium drops in 96-well plates; certain inhibitors were also tested in upright drops with or without an oil overlay.

RESULTS

The oxidative phosphorylation inhibitor rotenone (0.1, 0.5 and 1 micromol/l) totally abolished follicle growth in the inverted system; cyanide (1 mmol/l) totally abolished growth in the upright with oil system but not in the inverted system (possibly due to loss of cyanide gas due to the absence of an oil overlay). The mitochondrial uncoupler 2,4-dinitrophenol (0.5 and 1 mmol/l) also abolished growth in the inverted system. The TCA cycle inhibitor monofluoroacetate (10 mmol/l), significantly inhibited growth in all three culture systems (P < 0.01) but malonate (10 mmol/l) had no effect.

CONCLUSIONS

Aerobic metabolism and an adequate oxygen supply are essential for normal follicular development.

Carotid sinus nerve responses and ventilatory acclimatization to hypoxia in adult rats following 2 weeks of postnatal hyperoxia

Adult rats have decreased carotid body volume and reduced carotid sinus nerve, phrenic nerve, and ventilatory responses to acute hypoxic stimulation after exposure to postnatal hyperoxia (60% O2, PNH) during the first 4 weeks of life. Moreover, sustained hypoxic exposure (12%, 7 days) partially reverses functional impairment of the acute hypoxic phrenic nerve response in these rats. Similarly, 2 weeks of PNH results in the same phenomena as above except that ventilatory responses to acute hypoxia have not been measured in awake rats. Thus, we hypothesized that 2-week PNH-treated rats would also exhibit blunted chemoafferent responses to acute hypoxia, but would exhibit ventilatory acclimatization to sustained hypoxia. Rats were born into, and exposed to PNH for 2 weeks, followed by chronic room-air exposure. At 3-4 months of age, two studies were performed to assess: (1) carotid sinus nerve responses to asphyxia and sodium cyanide in anesthetized rats and (2) ventilatory and blood gas responses in awake rats before (d0), during (d1 and d7), and 1 day following (d8) sustained hypoxia. Carotid sinus nerve responses to i.v. NaCN and asphyxia (10 s) were significantly reduced in PNH-treated versus control rats; however, neither the acute hypoxic ventilatory response nor the time course or magnitude of ventilatory acclimatization differed between PNH and control rats despite similar levels of PaO2 . Although carotid body volume was reduced in PNH rats, carotid body volumes increased during sustained hypoxia in both PNH and control rats. We conclude that normal acute and chronic ventilatory responses are related to retained (though impaired) carotid body chemoafferent function combined with central neural mechanisms which may include brainstem hypoxia-sensitive neurons and/or brainstem integrative plasticity relating both central and peripheral inputs.

Reciprocal modulation of O2 and CO2 cardiorespiratory chemoreflexes in the tambaqui

This study examined the effect of acute hypoxic and hypercapnic cardiorespiratory stimuli, superimposed on existing cardiorespiratory disturbances in tambaqui. In their natural habitat, these fish often encounter periods of hypoxic hypercapnia that can be acutely exacerbated by water turnover. Tambaqui were exposed to periods of normoxia, hypoxia, hyperoxia and hypercapnia during which, externally oriented O2 and CO2 chemoreceptors were further stimulated, by administration into the inspired water of sodium cyanide and CO2-equilibrated water, respectively. Hyperoxic water increased the sensitivity of the NaCN-evoked increase in breathing frequency (f(R)) and decrease in heart rate. Hypoxia and hypercapnia attenuated the increase in f(R) but, aside from blood pressure, did not influence the magnitude of NaCN-evoked cardiovascular changes. Water PO2 influenced the magnitude of the CO2-evoked cardiorespiratory changes and the sensitivity of CO2-evoked changes in heart rate and blood flow. The results indicate that existing respiratory disturbances modulate cardiorespiratory responses to further respiratory challenges reflecting both changes in chemosensitivity and the capacity for further change.

Hypoxic activation of arterial chemoreceptors inhibits sympathetic outflow to brown adipose tissue in rats

In urethane-chloralose anaesthetized, neuromuscularly blocked, artificially ventilated rats, we demonstrated that activation of carotid chemoreceptors inhibits the elevated levels of brown adipose tissue (BAT) sympathetic nerve activity (SNA) evoked by hypothermia, by microinjection of prostaglandin E2 into the medial preoptic area or by disinhibition of neurones in the raphe pallidus area (RPa). Peripheral chemoreceptor stimulation with systemic administration of NaCN (50 microg in 0.1 ml) or with hypoxic ventilation (8% O2-92% N2, 30 s) completely inhibited BAT SNA. Arterial chemoreceptor-evoked inhibition of BAT SNA was eliminated by prior bilateral transections of the carotid sinus nerves or by prior inhibition of neurones within the commissural nucleus tractus solitarii (commNTS) with glycine (40 nmol/80 nl) or with the GABAA receptor agonist muscimol (160 pmol/80 nl; 77 +/- 10% attenuation), or by prior blockade of ionotropic excitatory amino acid receptors in the commNTS with kynurenate (8 nmol/80 nl; 82 +/- 10% attenuation). Furthermore, activation of commNTS neurones following local microinjection of bicuculline (30 pmol/60 nl) completely inhibited the elevated level of BAT SNA resulting from disinhibition of neurones in the RPa. These results demonstrate that hypoxic stimulation of arterial chemoreceptor afferents leads to an inhibition of BAT SNA and BAT thermogenesis through an EAA-mediated activation of second-order, arterial chemoreceptor neurones in the commNTS. Peripheral chemoreceptor-evoked inhibition of BAT SNA could directly contribute to (or be permissive for) the hypoxia-evoked reductions in body temperature and oxygen consumption that serve as an adaptive response to decreased oxygen availability.

Chemical activation of pre-Bötzinger complex in vivo reduces respiratory network complexity

In the in vivo anesthetized adult cat model, multiple patterns of inspiratory motor discharge have been recorded in response to chemical stimulation and focal hypoxia of the pre-Bötzinger complex (pre-BötC), suggesting that this region may participate in the generation of complex respiratory dynamics. The complexity of a signal can be quantified using approximate entropy (ApEn) and multiscale entropy (MSEn) methods, both of which measure the regularity (orderliness) in a time series, with the latter method taking into consideration temporal fluctuations in the underlying dynamics. The current investigation was undertaken to examine the effects of pre-BötC-induced excitation of phasic phrenic nerve discharge, which is characterized by high-amplitude, rapid-rate-of-rise, short-duration bursts, on the complexity of the central inspiratory neural controller in the vagotomized, chloralose-anesthetized adult cat model. To assess inspiratory neural network complexity, we calculated the ApEn and MSEn of phrenic nerve bursts during eupneic (basal) discharge and during pre-BötC-induced excitation of phasic inspiratory bursts. Chemical stimulation of the pre-BötC using DL-homocysteic acid (DLH; 10 mM; 10–20 nl; n = 10) significantly reduced the ApEn from 0.982 ± 0.066 (mean ± SE) to 0.664 ± 0.067 ( P < 0.001) followed by recovery (∼1–2 min after DLH) of the ApEn to 1.014 ± 0.067; a slightly enhanced magnitude reduction in MSEn was observed. Focal pre-BötC hypoxia (induced by sodium cyanide; NaCN; 1 mM; 20 nl; n = 2) also elicited a reduction in both ApEn and MSEn, similar to those observed for the DLH-induced response. These observations demonstrate that activation of the pre-BötC reduces inspiratory network complexity, suggesting a role for the pre-BötC in regulation of complex respiratory dynamics.

Rapid sodium cyanide depletion in cell culture media: Outgassing of hydrogen cyanide at physiological pH

During the course of in vitro studies on cyanide exposure with SH-SY5Y human neuroblastoma cells, we found that sodium cyanide (NaCN) up to a concentration of 10 mM had no significant toxic effect under our culture conditions. Further investigation of this apparent cyanide resistance revealed that the sodium cyanide was being rapidly depleted from the cell culture medium. Cyanide was interacting with constituents of the cell culture medium and was somehow being detoxified or removed from solution. The reaction of cyanide with cell culture media in 96-well culture plates reduced cyanide concentrations rapidly (80-90% in 2 h at 37 degrees C). Running the same reaction in capped tubes significantly reduced cyanide loss from solution. Incubation of cyanide with individual constituents of the cell culture medium in solution showed that glucose, phenol red, and amino acids all acted to detoxify or remove cyanide from solution. When amino acids or buffers were incubated with sodium cyanide in aqueous solution at pH 7.4, hydrogen cyanide (HCN) was found to degas from the solutions. We compared HCN outgassing over a range of pH values. As expected, HCN remained very soluble at high pH, but as the pH was reduced to 7.0, the rate of HCN formation and outgassing increased dramatically. Acid-base reactions involving cyanide and proton donors, such as amino acids and other cell culture media constituents, at physiological pH result in rapid HCN outgassing from solution at 37 degrees C. These results indicate that previous in vitro cyanide toxicity studies done in standard culture media with prolonged incubation times using gas-exchanging culture containers might have to be reevaluated in light of the fact that the effective cyanide concentrations in the culture media were significantly lower than reported.

N-PEP-12 – a novel peptide compound that protects cortical neurons in culture against different age and disease associated lesions

The neuroprotective potency of N-PEP-12, a novel, proprietary compound consisting of biopeptides and amino acids was investigated. Lesion models have been applied in neuronal cultures of embryonic chicken cortex, pre-treated with N-PEP-12 from the first day onwards. On day 8 in vitro neurons were lesioned and cell viability was measured 24 and 48 hours later. To simulate acute brain ischemia, cytotoxic hypoxia was induced by sodium cyanide or by iodoacetate and excitotoxicity by L-glutamate. Ionomycin for up to 48 hours induced calcium overload. The cytoskeleton was disrupted by addition of colchicine. N-PEP-12 shows dose-dependent neuroprotection in all different models. The effect size depends on the recovery time but also on the extent of the lesion. In cases of mild to moderate lesion pronounced dose-dependent effects could be demonstrated. This indicates that chronic exposure to N-PEP-12 is able to prevent neuronal cell death associated to conditions occurring during normal aging and neurological disorders like ischemic stroke, hypoxia, brain trauma, or AD.

[An enzyme-mediated mechanism of sodium nitroprusside NO-donating activity in the rat aorta]

The mechanisms of NO-mediated physiological activity of sodium nitroprusside (SNP) have been investigated in isolated rat aorta segments. It was shown, that in pretreated with 1.5 mM NaCN aorta segments SNP causes slight vasoconstriction. Heme-oxidizer K3Fe(CN)6 markedly suppressed SNP-induced vasodilatation. Also it was revealed that NaCN inhibits NO2- accumulation, which was observed in buffer solution with SNP after addition of microsomal membranes isolated from rat aorta homogenates. The great importance of cell membranes heme-containing enzymes for display of SNP NO-donating activity and the possibility of SNP-released CN- involvement in suppression of SNP-induced vasodilatation is discussed.

Cyanide inhibits the Na+/Ca2+ exchanger in isolated cardiac pacemaker cells of the cane toad

The effects of the metabolic inhibition on the activity of the Na+/Ca2+ exchanger (NCX) were studied in single isolated pacemaker cells from the cane toad. Ca2+ influx on NCX (reverse mode) was estimated by measuring the increase in intracellular calcium concentration ([Ca2+]i) in response to extracellular Na+-free solution. After application of 2 mM sodium cyanide for 3-5 min, the peak [Ca2+]i in Na+-free solution was significantly decreased from 377+/-42 nM to 260+/-46 nM, suggesting inhibition of NCX. To study Ca2+ efflux on NCX (forward mode), we recorded the tail currents on repolarization which were abolished by Ni2+ and by Na+-free solution. Cyanide decreased the amplitude of tail currents by 36+/-3%. To investigate the intrinsic properties of NCX during the metabolic inhibition, we used rapid application of caffeine to trigger sarcoplasmic reticulum Ca2+ release, which then stimulates NCX current (I(NCX) ). Both the caffeine-induced peak [Ca2+]i and the peak I(NCX) were reduced by cyanide exposure. When I(NCX) was plotted against [Ca2+], the slope of the decay phase was decreased in the presence of CN- to 44+/-8% of control, indicating that for a given [Ca2+]i there was less I(NCX) produced. These results show that cyanide (CN-) inhibits NCX activity at least partly through changes in the intrinsic properties of NCX. The inhibition of NCX probably contributes to the slower firing rate of pacemaker cells in CN-.

Chronic intermittent hypoxia enhances cat chemosensory and ventilatory responses to hypoxia

The carotid body (CB) chemoreceptors may play an important role in the enhanced hypoxic ventilatory response induced by chronic intermittent hypoxia (CIH). We studied the effects of cyclic hypoxic episodes of short duration on cat cardiorespiratory reflexes, heart rate variability, and CB chemosensory activity. Cats were exposed to cyclic hypoxic episodes (PO2 approximately 75 Torr) repeated during 8 h for 2-4 days. Cats were anaesthetized with sodium pentobarbitone (40 mg kg(-1) i.p., followed by 8-12 mg i.v.), and ventilatory and cardiovascular responses to NaCN (0.1-100 microg kg(-1) i.v.) and several isocapnic levels of oxygen (PO2 approximately 20-740 Torr) were studied. After studying the reflex responses, we recorded the CB chemosensory responses induced by the same stimuli. Results showed that CIH for 4 days selectively enhanced cat CB ventilatory (VT and VI) responses to hypoxia, while responses to NaCN remained largely unchanged. Similarly, basal CB discharges and responses to acute hypoxia (PO2 < 100 Torr) were larger in CIH than in control cats, without modification of the responses to NaCN. Exposure to CIH did not increase basal arterial pressure, heart rate, or their changes induced by acute hypoxia or hyperoxia. However, the spectral analysis of heart rate variability of CIH cats showed a marked increase of the low-/high-frequency ratio and an increase of the power spectral distribution of low frequencies of heart rate variability. Thus, the enhanced CB reactivity to hypoxia may contribute to the augmented ventilatory response to hypoxia, as well as to modified heart rate variability due to early changes in autonomic activity.

NaCN-induced chemical hypoxia is associated with altered gene expression

Sodium cyanide (NaCN)-induced chemical hypoxia is known to increase intracellular free calcium concentration and reduce cell survival, but its effect on gene expression has not been studied. In this study, we designed primers to conduct a rapid and reliable assay for the expression of mRNA of inducible nitric oxide synthase (iNOs), tumor suppressor protein p53, Bcl-2, heat shock protein 70 (HSP-70), and beta-actin in human intestinal epithelial T84 cells and Jurkat T cells. NaCN-induced chemical hypoxia increased iNOs and HSP-70 mRNA in both types of cells, whereas p53 and Bcl-2 mRNA were singularly induced in T84 cells and Jurkat T cells, respectively. In both cell types, treatment of hypoxic cells with a reversible selective iNOs inhibitor, Now-nitro-L-arginine (LNNA), blocked iNOs, Bcl-2, and HSP-70 mRNA, but increased p53. The NaCN-induced hypoxia was also found to increase caspase-3 cellular activity in both cell types. Treatment with LNNA alone decreased the basal caspase-3 cellular activity. A prior treatment of LNNA significantly inhibited the NaCN-induced increase in the cellular activity of this apoptotic enzyme. This is the first report to show that NaCN-induced chemical hypoxia alters both stress-related gene expression and caspase-3 cellular activity and can be regulated by the iNOs inhibitor LNNA. Since NaCN has been included in the 'National chemical terrorism threat' list, by the US Department of Defense, our studies provide useful insight in the development of molecular sensors to detect early exposure to this chemical terrorism threat.

NHE-1 and NBC during pseudo-ischemia/reperfusion in rabbit ventricular myocytes

Despite many studies into the pathophysiology of cardiac ischemia-reperfusion injury, a number of key details are as yet undisclosed. These include the timing and magnitude of the changes in both Na(+)/H(+) exchange (NHE-1) and Na(+) -- HCO(3)(-) -cotransport (NBC) transport rates. We fluorimetrically measured H(i)(+) fluxes (J(NHE-1) and J(NBC)) and Na(i)(+) fluxes in single contracting rabbit ventricular myocytes subjected to metabolic inhibition, pseudo-ischemia (i.e. metabolic inhibition and extracellular acidosis of 6.4), and pseudo-reperfusion. Metabolic inhibition and pseudo-ischemia inhibited NHE-1 by 43 +/- 3.1% and 91 +/- 3.6%, and NBC by 66 +/- 5.4% and 100%, respectively. Inhibition was due to both an acidic shift of the pH(i) at which NHE-1 and NBC become quiescent (set-point pH(i)) and a reduction of the steepness of the pH(i) -- H(i)(+) flux profiles. NHE-1 and NBC did not contribute to Na(i)(+) loading during metabolic inhibition (Na(i)(+) 18 +/- 1.7 mM) or pseudo-ischemia (Na(i)(+) 21 +/- 1.7 mM), because pH(i) acidified less than set-point pH(i)'s. Upon pseudo-reperfusion NBC recovered to 54 +/- 7.3% but NHE-1 to 193 +/- 11% of aerobic control flux, and set-point pH(i)'s returned to near neutral values. Metabolic inhibition and reperfusion caused an acid load of 18 +/- 3.2 mM H(+) 94% of which were extruded by the hyperactive NHE-1. At pseudo-reperfusion Na(i)(+) rose sharply to 31 +/- 5.8 mM within 1.5 min and that coincided with hypercontracture. Cariporide not only prevented the Na(i)(+) transient, but also inhibited pH(i) recovery and prevented hypercontracture. Our results are consistent with the view that NHE-1 is active during metabolic inhibition if, like in whole hearts, pH(i) is driven more acidic than NHE-1 set-point pH(i). Furthermore, either an acidic pH(i) or absence of additional Na(i)(+) loading during reperfusion, or both, limit ischemia-reperfusion injury.

Intermittent hypoxia augments carotid body and ventilatory response to hypoxia in neonatal rat pups

Carotid bodies are functionally immature at birth and exhibit poor sensitivity to hypoxia. Previous studies have shown that continuous hypoxia at birth impairs hypoxic sensing at the carotid body. Intermittent hypoxia (IH) is more frequently experienced in neonatal life. Previous studies on adult animals have shown that IH facilitates hypoxic sensing at the carotid bodies. On the basis of these studies, in the present study we tested the hypothesis that neonatal IH facilitates hypoxic sensing of the carotid body and augments ventilatory response to hypoxia. Experiments were performed on 2-day-old rat pups that were exposed to 16 h of IH soon after the birth. The IH paradigm consisted of 15 s of 5% O2 (nadir) followed by 5 min of 21% O2 (9 episodes/h). In one group of experiments (IH and control, n = 6 pups each), sensory activity was recorded from ex vivo carotid bodies, and in the other (IH and control, n = 7 pups each) ventilation was monitored in unanesthetized pups by plethysmography. In control pups, sensory response of the carotid body was weak and was slow in onset (approximately 100 s). In contrast, carotid body sensory response to hypoxia was greater and the time course of the response was faster (approximately 30 s) in IH compared with control pups. The magnitude of the hypoxic ventilatory response was greater in IH compared with control pups, whereas changes in O2 consumption and CO2 production during hypoxia were comparable between both groups. The magnitude of ventilatory stimulation by hyperoxic hypercapnia (7% CO2-balance O2), however, was the same between both groups of pups. These results demonstrate that neonatal IH facilitates carotid body sensory response to hypoxia and augments hypoxic ventilatory chemoreflex.

Myocyte protection by 10 kD heat shock protein (Hsp10) involves the mobile loop and attenuation of the Ras GTP-ase pathway

Heat shock proteins (hsp), hsp60 and hsp10, are involved in the folding of imported mitochondrial proteins and the refolding of denatured proteins after stress. We examined whether hsp10 can reduce myocyte death by its mitochondrial function or by interacting with cytoplasmic signaling pathways. Overexpression of hsp10 by adenoviral infection decreased myocyte death induced by hydrogen peroxide, sodium cyanide, and simulated ischemia and reoxygenation (SI/RO). We generated an adenoviral vector coding for a temperature-sensitive mutant hsp10 protein (P34H), incapable of cooperatively refolding denatured malate dehydrogenase with hsp60. Overexpression of the hsp10 mutant potentiated SI/RO-induced myocyte death. Analysis of electron transport chain function revealed increased Complex I capacity with hsp10 overexpression, whereas hsp10(P34H) overexpression decreased Complex II capacity. Hsp10 overexpression preserved both Complex I and II function after SI/RO. Examination of the Ras GTP-ase signaling pathway indicated that inhibition of Ras was required for protection by hsp10. Constitutive activation of Ras abolished the effects afforded by hsp10 and hsp10(P34H). Hsp10 overexpression inactivated Raf, ERK, and p90Ribosomal kinase (p90RSK) before and after SI/RO. Our results suggest that complex mechanisms are involved in the protection by hsp10 against SI/RO-induced myocyte death. This mechanism may involve the hsp10 mobile loop and attenuation of the Ras GTP-ase signaling pathway.

Interactive effects of mechano- and chemo-receptor inputs on cardiorespiratory outputs in the toad

Arterial blood pressure (P(b)), pulmocutaneous blood flow (Q(pc)), heart rate (f(H)), and fictive ventilation (motor activity in the Vth cranial nerve, V(int)), were recorded from decerebrated, paralysed toads receiving unidirectional ventilation with experimental gas mixtures over a range of lung inflation. At the onset of spontaneous bouts of fictive ventilation, (Q(pc)) and P(b) increased immediately, often with changes in heart rate, implying central cardiorespiratory interactions. Inflation of the lungs with different gas mixtures revealed that the effect of hypercarbia on V(int) was reduced by lung inflation and that feedback from pulmonary stretch receptors may summate with central feedforward control of f(H) and (Q(pc)) in an interactive fashion. The results of bolus injections of cyanide into the carotid or the pulmonary circulations suggest there are oxygen sensitive receptors in both circuits that affect the cardiovascular system directly and respiratory activity by complex central interactions with inputs from central chemoreceptors and pulmonary stretch receptors.

Disposition and intracellular levels of moxifloxacin in human THP-1 monocytes in unstimulated and stimulated conditions

Moxifloxacin uptake by human THP-1 monocytes was passive and initially linear and reached equilibrium after approximately 4 h. High intracellular concentrations were achieved and intracellular/extracellular [I/E] ratios were between 1925 and 4575 for the lowest concentration of 0.004 microg/ml at pH 7.4 and 6.9. The uptake of moxifloxacin was reduced by sodium fluoride, -azide, -cyanide, low temperature and low pH. However, the uptake was not affected by any of the ion channel blockers. Adenosine demonstrated marginal competition with moxifloxacin for uptake suggesting a nucleoside transporter may be involved. The sodium-ATPase pump when blocked, also retarded moxifloxacin uptake at 2 and 4 h. This I/E ratio was high compared with other macrolides and indicateed that the monocyte may contain sufficient moxifloxacin levels to conduct the antibiotic throughout systemic circulation to infection sites. Efflux from THP-monocytes was essentially complete after 2 h indicating no long term sequestering of the antibiotic occurred. Disposition of the antibiotic within the THP-1 monocytes showed large amounts present in the nucleus and cytoplasm in stimulated and unstimulated cells. Increased amounts of the drug were found in the THP-1 monocytes as well as the endoplasmic reticulum and the isolated phagosomes after stimulation by zymogen A, Staphylococcus aureus or Streptococcus pneumoniae.