Effects of patulin on adenosine triphosphatase activities in the mouse.

Patulin (4-hydroxy-4H-furol3,2clpyran-2(6H)-one), a toxic metabolite of various species of Aspergillus and Penicillium, differentially inhibited (in vitro) the Na⁺K⁺-activated and the oligomycin-sensitive and insensitive Mg²⁺-adenosine triphosphatase activities of mouse brain, kidney, and liver fractions containing nerve endings, mitochondria, and endoplasmic reticulum (B), and microsomal preparations (C) from these tissues. A dose-dependent inhibition of Na⁺K⁺-ATPase activity in brain and kidney tissue fractions B and C was observed with corresponding ID50 (50% inhibition) values of 3.0 and 3.7 × 10^?4m patulin for brain and kidney B fractions and 3.4 and 2.0 × 10^?4m patulin for brain and kidney C fractions, respectively. Oligomycin-sensitive mitochondrial Mg²⁺-ATPase of brain, kidney, and liver also were inhibited by patulin in both preparations but less drastically than by the Na⁺K⁺-ATPase system. Oligomycin-insensitive Mg²⁺ activities of brain and kidney were only slightly affected with computed ID50 values of 1.0 and 2.0 × 10^?3m patulin for B fractions and 3.0 and 6.0 × 10^?3m patulin for C fractions, respectively. In vivo oligomycin-sensitive Mg²⁺ ATPase activities in B preparations from liver and kidneys of mice pretreated with 7.5 mg/kg were inhibited 52 and 28%, respectively, after 48 hr. Furthermore, kidney Na⁺K⁺-ATPase activity from the same preprations was significantly correspondingly inhibited. Although oligomycin-sensitive and Na⁺K⁺-ATPase activities were not affected in brain, oligomycin-insensitive ATPase activity was slightly reduced in vivo. Thus, in vitro and in vivo results suggest possible patulin-mediated effects in the mouse through disruption of adenosine triphosphatase systems.     

Reversible inhibition of mammalian brain acetylcholinesterase and sodium potassium-stimulated adenosine triphosphatase by cyclopropane.

Membrane-bound and purified forms of acetylcholinesterase (AChE) derived from beef brain caudate nucleus tissue were inhibited reversibly by cyclopropane at low gas pressures (0.025 to 0.25 atm). Inhibition followed mixed kinetics which suggested interactions of the anesthetic gas with both active sites(s) and other sites on the enzyme molecule. At gas pressures of 1 atm and higher, cyclopropane inhibited membrane-bound and solubilized preparations of brain Na⁺-K⁺-ATPase without affecting Mg²⁺-ATPase activity. This inhibition was reversible, followed uncompetitive kinetics and was not due to pressure per se. AT³²P-labeling experiments suggested that cyclopropane inhibited Na⁺-K⁺ATPase at or before the phosphorylation step in the enzyme reaction cycle.     

Effect of penicillic acid on adenosine triphosphatase activity in the mouse.

The effect of penicillic acid on mouse tissue ATPase was examined both in vitro and in vivo. Penicillic acid inhibited in vitro the (Na⁺, K⁺)-activated ATPase in the 13,000g (B) fraction in a dose-dependent manner with calculated I50 values of 2.5 and 3.3 × 10^?5m for brain and kidney, respectively. Similar inhibition in the microsomal fraction also was observed with I50 values of 6.0 and 1.0 × 10^?5m for brain and kidney tissues, respectively. Brain and kidney (Na⁺, K⁺)-ATPase activity also was inhibited by penicillic acid in vivo. An inhibition time response of (Na⁺, K⁺)-stimulated ATPase in brain and kidney tissue from mice receiving 80 mg/kg penicillic acid in saline was noted while a dose-dependent effect was demonstrated in the brain microsomal fraction and in the kidney B and microsomal fractions. Mg²⁺-Activated ATPase activity was not significantly impaired except for oligomycin-insensitive Mg²⁺-ATPase in the brain B fraction. Thus, in vitro and in vivo results suggested a possible correlation between inhibition of (Na⁺, K⁺)-ATPase activity and penicillic acid-mediated toxicity.     

Effect of rubratoxin B on adenosine triphosphatase activities in the mouse.

Half the animals in groups of selenium-deficient and control rats were given mercury in the drinking water for 6 weeks. The other half of the animals in both groups received tap water ad libitum. Selenium-deficient rats gained significantly less weight when given mercury, but weight gain of controls was unaffected by mercury administration. In another experiment with rats given mercury for 8 weeks, serum creatinine and renal histology were normal in selenium-deficient and control rats. Selenium-deficient rats injected with ²⁰³HgCl₂ 12 days after mercury was added to their drinking water excreted up to 10% of the ²⁰³Hg in the urine in the first 24 hr whereas control animals excreted less than 2%. This trend continued for several days and was shown to be due primarily to a loss of ²⁰³Hg from the kidney in the selenium-deficient rats. The control kidneys contained 4 times as much mercury as the kidneys in selenium-deficient rats at the end of the experiment, and the mercury content appeared to be increasing further. Selenium-deficient kidneys, however, had achieved maximum mercury accumulation by 13 days. Despite the large differences in mercury accumulation due to selenium status, in both groups about 80% of kidney ²⁰³Hg was found in the soluble fraction. Also, regardless of selenium status, about 90% of the soluble fraction ²⁰³Hg was found in a symmetrical peak on gel filtration which probably represents metallothionein. Thus a major effect of selenium status on the metabolism of inorganic mercury seems to be in facilitating the accumulation of mercury by the kidney. Since most of the kidney mercury is bound to metallothionein, selenium may mediate the binding of mercury to this protein or be a permissive factor in the induction of metallothionein by mercury.     

Effects of DDT on eggshell quality and calcium adenosine triphosphatase.

Adult mallard ducks were fed a diet containing 50 ppm DDT for 6 months. Eggs laid during this period were collected and eggshell weight, thickness, and calcium were determined. Chronic ingestion of DDT resulted in production of eggshells that were significantly thinner and lighter than those of controls. Total calcium of thinned eggshells was also reduced; however, calcium per gram of eggshell was not altered, indicating that other eggshell constituents were not incorporated as well. Calcium adenosine triphosphatase activity in the microsomal fraction of eggshell gland epithelium was assayed in control and DDT-fed ducks. Enzyme activity in DDT-fed ducks was reduced to 65% of control values. Since Ca-ATPase has been shown to be associated with calcium transport, enzyme inhibition may be responsible for decreased eggshell weight and thickness. Electron microscopic evaluation of microsomal fractions showed elements of the plasma membrane, including cilia and microvilli, as well as rough and smooth endoplasmic reticulum. Inhibition of calcium transport at the plasma membrane of mucosal epithelium is proposed as a possible mechanism of DDT-induced eggshell thinning.     

Effect of phospholipase A treatment on the partial reactions of and ouabain binding to a purified sodium and potassium activated adenosine triphosphatase.

The effects of phospholipase A treatment on ouabain binding to and the partial reactions of a purified, mammalian NaK-ATPase (sodium and potassium activated adenosine triphosphatase) preparation were investigated. The treatment removed 70 per cent of the lipid phosphate without altering the relative quantities of the two protein subunits. Hydrolytic activity was reduced 70 per cent. whereas K⁺ phosphatase and steady-state phosphorylation (minus K⁺) were inhibited by 30 per cent, The phosphoenzyme formed was insensitive to both K⁺ and ADP at 0°, but not at 22°. The number of [³H]ouabain binding sites was not affected at 30°, but the rates of binding in the presence of Mg²⁺ plus inorganic phosphate and Mg²⁺ ATP, sodium and potassium were reduced. At 0°, both the rates of binding and the apparent number of binding sites were markedly reduced.     

Effects of purified components of jellyfish toxin (Stomolophus meleagris) on adenosine triphosphatase activities.

Toxin from the jellyfish Stomolophus meleagris was found to stimulate both Na⁺-K⁺ and mitochondrial Mg²⁺ ATPase activities at low toxin concentrations and to inhibit these ATPase activities at higher (> 0·2 mg/ml) concentrations. Using discontinuous membrane partition chromatography the toxin was fractionated into six fractions. Of these six fractions, one strongly activated when five inhibited mitochondrial Mg²⁺ ATPase. One fraction strongly activated, a second mildly activated, while the other four inhibited Na⁺-K⁺ ATPase about 50 per cent. Only two fractions affected oligomycin-insensitive ATPase, and both of these exhibited a mild stimulation. It is concluded that the ability of this toxin to alter membrane permeability to Na⁺ is due, at least in part, to components in the toxin which act directly on ATPase.     

Effects of general anaesthetics on neuronal sodium and potassium channels.

1. The effects of clinical inhalation anaesthetics, such as halothane and methoxyflurane, and "model" anaesthetics, such as hydrocarbons and n-alkanols, on neuronal sodium and potassium channels are reviewed. 2. Lipid-based mechanisms for the actions of anaesthetics on the gating parameters of squid axon sodium and delayed rectifier potassium currents are considered in conjunction with evidence of more specific effects in other preparations, notably a fast inactivating potassium current in Helix neurones and a voltage-gated sodium current in rat dorsal root ganglion neurones. 3. The proconvulsant actions of some inhalation anaesthetics are discussed in relation to the induction of spontaneous firing of action potentials in the squid giant axon.     

Effects of ifenprodil on the adenosine triphosphatase of guinea pig liver mitochondria]

The effects of ifenprodil on adenosine triphosphatase (ATPase) activity were examined using guinea pig liver mitochondria. 1) Intact mitochondrial ATPase activity was stimulated by ifenprodil in a concentration-dependent manner, this effect being further potentiated with dinitrophenol. The stimulation by ifenprodil appeared with only ATP among four nucleotides as substrate. Mg2+ and Ca2+ attenuated the effect of ifenprodil. Ifenprodil abolished the KCN-induced inhibition. 2) Heat-treated mitochondrial ATPase activity, kept for 60 min at 50 degrees C, was decreased in a concentration-dependent manner by ifenprodil. The inhibitory effect of ifenprodil was abolished by Mg2+ and Ca2+. These results indicate that ifenprodil has two behaviors, acceleration of a latent ATPase and inhibition of an activated ATPase. These findings, together with our previous data, suggest that ifenprodil seems to affect the actions of Mg2+ and Ca2+ on mitochondrial ATPase by directly affecting the membrane, and these mechanisms may be involved in its anti-cyanide effect.