Purification and partial characterization of oxalate oxidase from leaves of forage Sorghum (Sorghum vulgare var. KH-105) seedlings.

An oxalate oxidase was purified to apparent homogeneity from the leaves of 10-days old seedlings of forage Sorghum (Sorghum vulgare var. KH-105). The enzyme had a Mr of 124 kDa with two identical subunits, an optimum pH of 4.5, optimum temperature of 37 degrees C and activation energy (Ea) of 2.0338 Kcal/mol. The rate of reaction was linear up to 7 min. K(m) value for oxalate was 0.22 mM. The enzyme was stimulated by Cu2+ and inhibited by EDTA, NaCN, diethyldithiocarbamate, Na2SO4, but unaffected by NaCl at 0.1 mM concentration. Although the enzyme was stimulated by flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), UV and visible spectra of the enzyme did not match with that of a flavoprotein. The positive reaction of the enzyme with orcinol-H2SO4 reagent indicated its glycoprotein nature. The superiority of the purified enzyme over earlier reported oxalate oxidases for determination of urinary oxalate has been demonstrated.

[Protective effect of hydroxysafflor yellow A on experimental cerebral ischemia in rats].

AIM: To investigate the protective effect of hydroxysafflor yellow A (HSYA), a soluble element extracted from Carthamus tinctorius L., on focal cerebral ischemia in rats. METHODS: Focal cerebral ischemia in male Wistar-Kyoto (WKY) rats were induced by permanent middle cerebral artery occlusion (MCAO). Three doses of 1.5, 3.0 and 6.0 mg x kg(-1) of HSYA were administrated to three groups of rats, separately, via sublingular vein injection 30 min after the onset of ischemia. 24 h after ischemia in rats, neurological deficit scores were evaluated and the infarction area of brain was assessed by quantitative image analysis. The in vitro neuroprotective effect of HSYA was tested in cultured fetal cortical neurons exposed to glutamate and sodium cyanide (NaCN). RESULTS: HSYA at doses of 3.0 and 6.0 mg x kg(-1) exerted significant neuroprotective effects on rats with focal cerebral ischemic injury as expressed by neurological deficit scores and reduced the infarct area as compared with saline group, and the potency of HSYA at dose of 6.0 mg x kg(-1) was similar to that of 0.2 mg x kg(-1) of nimodipine. In vitro studies, HSYA significantly inhibited neurons damage induced by exposure to glutamate and NaCN in cultured fetal cortical cells. CONCLUSION: HSYA has potential neuroprotective action against focal cerebral ischemia in rats and cultured rat fetal cortical neurons as well.

Plasma membrane hyperpolarization by cyanide in chromaffin cells: role of potassium channels.

Exposure of rat pheochromocytoma (PC12) cells to cyanide produces elevation of cytosolic calcium, impaired Na(+)-H+ exchange, membrane lipid peroxidation and release of neurotransmitters. Since these observations suggested cyanide alters plasma membrane function, the present study examined the effect of NaCN on the membrane potential of undifferentiated PC12 cells in suspension. In PC12 cells loaded with the voltage sensitive fluorescent dye, bis-oxonol, cyanide (2.5-10 mM) elicited an immediate (within seconds), concentration related decrease in fluorescence, indicating hyperpolarization of the plasma membrane. Increasing extracellular K+ concentration to 20 mM blocked the effect of cyanide (5 mM), suggesting cyanide increased K+ efflux. Pretreatment with quinine blocked the cyanide-induced hyperpolarization, whereas glyburide had little effect, showing the hyperpolarization produced by cyanide was due to activation of Ca2+ sensitive K+ channels. Removal of Ca2+ from the media did not influence cyanide-induced hyperpolarization. However, buffering intracellular Ca2+ by loading cells with the Ca2+ chelators, Quin II or BAPTA, abolished the cyanide effect, showing cytosolic Ca2+ is a key factor. These findings suggest that cyanide mobilizes Ca2+ from intracellular stores which leads to hyperpolarization via the activation of Ca2+ sensitive K+ channels.

Phospholipid metabolism and intracellular Ca2+ homeostasis in cultured rat hepatocytes intoxicated with cyanide.

The killing of cultured hepatocytes by 1 mM sodium cyanide was reduced by 100 microM chlorpromazine or cytochalasin B (25 micrograms/ml) or by lowering the pH of the culture medium to 6.0. In each case, ATP was depleted despite the decreased number of dead cells. The cell killing by cyanide was accompanied by an accelerated release of 3H-labeled arachidonate from phospholipids. Depletion of ATP by oligomycin did not accelerate phospholipid degradation or kill the hepatocytes. Chlorpromazine, cytochalasin B, and extracellular acidosis reduced the rate of phospholipid degradation in control cells as well as the increase that occurred with cyanide. The calcium ionophore A23187 increased phospholipid degradation and killed the hepatocytes. Chlorpromazine and extracellular acidosis, but not cytochalasin B, protected the cells and prevented the increased lipid degradation in response to A23187. After addition of cyanide, cytosolic free calcium ([Ca2+]i) did not change for 71 +/- 8 min, at which time it rose to a plateau of 683 +/- 210 nM within 10 min. A second and larger rise occurred after 84 +/- 8 min and before the death of the cells at 89 +/- 8 min. Treatment with 3.5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, as well as removal of extracellular calcium, prevented these late increases in [Ca2+]i without affecting the loss of viability. It is concluded that cyanide kills cultured hepatocytes by a mechanisms that is likely related to an accelerated degradation of phospholipids. This change in lipid metabolism is not mediated by a rise in [Ca2+]i but rather may relate to an alteration in the interaction between the cytoskeleton and the plasma membrane.

Blockade of N-methyl-D-aspartate receptors prevents cyanide-induced neuronal injury in primary hippocampal cultures.

Cyanide-induced alterations of cytosolic calcium levels and cytotoxicity were examined in primary cultures of rat hippocampus. Cytosolic free Ca2+ ([Ca2+]i) levels were measured in hippocampal neurons using the fluorescent probe, fura 2. A concentration-dependent rise in [Ca2+]i occurred rapidly following exposure of cells to 0.5-10 mM NaCN. In normal medium (1.3 mM Ca2+), 2 mM NaCN produced an increase in [Ca2+]i (172 +/- 27% of control), 45 sec following exposure. Ca2+ elevation produced by NaCN was blocked by removal of Ca2+ from the external medium or by pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonovalerate (APV). The cytotoxicity of cyanide, assessed by measuring the efflux of lactate dehydrogenase, was blocked by APV. These results indicate that in hippocampal neurons, cytosolic Ca2+ accumulation induced by cyanide originates from the extracellular compartment and the NMDA receptor ionophore is a significant route for Ca2+ entry. It is proposed that excitotoxic mechanisms may contribute to altered neuronal homeostasis and injury associated with cyanide.

Differential effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 in the cat.

Effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 were investigated using an in situ perfusion technique. Cats were anesthetized, paralyzed, and artificially ventilated. To avoid a possible reaction between an oligomycin-ethanol mixture and blood, we administered oligomycin to the carotid body via cell- and protein-free perfusate. Except for the perfusion periods, the carotid body received its own natural blood supply. Responses to O2, CO2, sodium cyanide, and nicotine of the same carotid chemoreceptor afferents were studied before and after each perfusion. An appropriate low dose of oligomycin completely blocked carotid chemoreceptor response to O2 while preserving the CO2 response. At the same time cyanide response was attenuated leaving nicotine response intact. Additional doses of oligomycin attenuated carotid chemoreceptor response to CO2 as well. Perfusion with a blank solution containing ethanol did not change the carotid body chemoreceptor responses. These effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 were reversible, and restoration of the response to CO2 preceded that to O2. In addition, oligomycin administered into the blood with close intra-arterial injection produced similar differential blockade of O2 and CO2 chemoreception, preserving the nicotine and dopamine effects. This study confirmed the previous findings and provided new evidence showing that 1) the responses of carotid chemoreceptor to O2 and CO2 were separable by oligomycin due to the inhibition of oxidative phosphorylation and 2) the responses to nicotine and dopamine were intact even after blockade of O2 response.

Alteration of chemoreflex phrenic responses by oligomycin in the rabbit.

The effects of carotid chemoreceptor stimulation by intracarotid injections of sodium cyanide (NaCN, 30 micrograms), antimycin A (AMC, 10 micrograms) and dopamine (DA, 10 micrograms) on phrenic nerve activity were studied before and after oligomycin (200 micrograms) in the rabbit. The excitatory responses to NaCN and AMC were abolished after intracarotid administration of oligomycin, whereas the DA-induced phrenic depression was only slightly diminished. In addition, the effects of hypoxia on phrenic nerve activity were also studied before and after oligomycin (200 micrograms) in some animals with denervated one carotid sinus nerve. The hypoxia-induced phrenic excitation was greatly reduced after intracarotid administration of oligomycin. These results indicate that the chemoreflex phrenic responses induced by NaCN, AMC and hypoxia are probably related to the phosphate potential in the carotid body.

Effects of sodium cyanide upon swimming performance in guinea-pigs and the conferment of protection by pretreatment with p-aminopropiophenone.

The swimming performance of guinea-pigs was degraded following administration of sodium cyanide (NaCN) at doses which were not lethal for individual animals. Decrements in performance were observed two minutes following subcutaneous administration of NaCN, were maximal at 8-16 minutes and, at the highest dose tested, did not return to control levels until 64-128 minutes. Pretreatment with p-aminopropiophenone (PAPP) at a dose inducing 7-15% methemoglobinemia (met.Hb), 15-90 minutes after administration, protected animals against the effects of NaCN upon swimming performance. However, the protection decreased as the interval between PAPP and NaCN was increased from 15 to 75 minutes. These data suggested that NaCN may affect both motor and cognitive function in guinea-pigs. The relevance of this animal model for predicting the behavioural effects of cyanide poisoning for assessing the protective efficacy of pretreatment with PAPP in humans is discussed.

Effect of antagonists on the physiologic disposition of sodium cyanide.

Attempts were made to evaluate the effects of pretreatment with air and oxygen either alone or in various combinations with sodium nitrite and/or sodium thiosulfate on the physiological disposition of 14C-labeled sodium cyanide in mice. The radioactive respiratory excretion was studied by radiorespirometry, and the effects of various combinations of cyanide antagonists were compared. Oxygen either alone or in combination with sodium thiosulfate significantly enhanced the respiratory excretion when compared with air. Sodium thiosulfate accelerated the initial rate, but not the total amount of radioactivity excreted. The cumulative recovery of radioactive gases was significantly greater with groups receiving oxygen either alone or with sodium thiosulfate. When sodium nitrite was employed as an antidote either alone or with sodium thiosulfate, no difference in the respiratory excretion was noted between air and oxygen. The use of the sodium nitrite-sodium thiosulfate combination either with air or oxygen resulted in a marked decrease in the initial rate as well as the total amount of respiratory radioactivity excreted. No significant differences between various experimental groups were noted in the total amount of urinary radioactivity excreted or the total body retention of radioactivity.

Cardiovascular and respiratory effects of some anesthetics in the decerebrate rat.

The cardiovascular and respiratory effects of pentobarbital, ketamine, chloralose and urethane were studied in decerebrate rats. All the anesthetics reduced blood pressure and heart rate. Pentobarbital, chloralose and ketamine, but not urethane, reduced respiratory rate. None of these agents had a significant effect on tidal volume. All these anesthetics significantly attenuated the carotid occlusion, tilt and sodium cyanide chemo-receptor response. These results suggest that the decerebrate rat may be a more suitable preparation, compared to the anesthetized one, for studying cardiovascular and respiratory responses in this species.