PO2 of the metathoracic ganglion in response to progressive hypoxia in an insect

Mammals regulate their brain tissue P_O2 tightly, and only small changes in brain P_O2 are required to elicit compensatory ventilation. However, unlike the flow-through cardiovascular system of vertebrates, insect tissues exchange gases through blind-ended tracheoles, which may involve a more prominent role for diffusive gas exchange. We tested the effect of progressive hypoxia on ventilation and the P_O2 of the metathoracic ganglion (neural site of control of ventilation) using microelectrodes in the American locust, Schistocerca americana. In normal air (21 kPa), P_O2 of the metathoracic ganglion was 12 kPa. The P_O2 of the ganglion dropped as air P_O2 dropped, with ventilatory responses occurring when ganglion P_O2 reached 3 kPa. Unlike vertebrates, insects tolerate relatively high resting tissue P_O2 levels and allow tissue P_O2 to drop during hypoxia, activity and discontinuous gas exchange before activating convective or spiracular gas exchange. Tracheated animals, and possibly pancrustaceans in general, seem likely to generally experience wide spatial and temporal variation in tissue P_O2 compared with vertebrates, with important implications for physiological function and the evolution of oxygen-using proteins.     

Genetic Coadaptation in the Chromosomal Polymorphism of DROSOPHILA SUBOBSCURA. I. Seasonal Changes of Gametic Disequilibrium in a Natural Population

Seasonal changes in gene arrangement and allozyme frequencies have been investigated in Drosophila subobscura for several years. Some arrangements (O_st and O₃₊₄₊₇) show seasonal variation, which suggests that chromosomal polymorphism is flexible in this species. Seasonal changes in allozyme frequencies for Lap and Pept-1 loci, both located within the same inversions of chromosome O, are significant only inside the O_st arrangement, but not inside O₃₊₄ arrangement. This arrangement-dependent response of allozyme generates variation in arrangement-allozyme disequilibrium. The historical hypothesis on the maintenance of disequilibria cannot explain these seasonal changes, and some kind of natural selection must be invoked. Association between Lap and Pept-1 is also seasonal inside O_st but not inside O₃₊₄. We propose that O_st probably consists of a finite array of supergenes that are differentially favored in each season by natural selection. The present evidence on this supergene selection and other genetic, biogeographic and phylogenetic data points to O₃₊₄ as the most primitive gene order among the present arrangements.     

Root Growth and Oxygen Relations at Low Water Potentials. Impact of Oxygen Availability in Polyethylene Glycol Solutions

Polyethylene glycol (PEG), which is often used to impose low water potentials (ψ_w) in solution culture, decreases O₂ movement by increasing solution viscosity. We investigated whether this property causes O₂ deficiency that affects the elongation or metabolism of maize (Zea mays L.) primary roots. Seedlings grown in vigorously aerated PEG solutions at ambient solution O₂ partial pressure (pO₂) had decreased steady-state root elongation rates, increased root-tip alanine concentrations, and decreased root-tip proline concentrations relative to seedlings grown in PEG solutions of above-ambient pO₂ (alanine and proline accumulation are responses to hypoxia and low ψ_w, respectively). Measurements of root pO₂ were made using an O₂ microsensor to ensure that increased solution pO₂ did not increase root pO₂ above physiological levels. In oxygenated PEG solutions that gave maximal root elongation rates, root pO₂ was similar to or less than (depending on depth in the tissue) pO₂ of roots growing in vermiculite at the same ψ_w. Even without PEG, high solution pO₂ was necessary to raise root pO₂ to the levels found in vermiculite-grown roots. Vermiculite was used for comparison because it has large air spaces that allow free movement of O₂ to the root surface. The results show that supplemental oxygenation is required to avoid hypoxia in PEG solutions. Also, the data suggest that the O₂ demand of the root elongation zone may be greater at low relative to high ψ_w, compounding the effect of PEG on O₂ supply. Under O₂-sufficient conditions root elongation was substantially less sensitive to the low ψ_w imposed by PEG than that imposed by dry vermiculite.     

Photorespiration and Oxygen Inhibition of Photosynthesis in Chlorella pyrenoidosa

The inhibition of photosynthesis by O₂ in air-grown Chlorella pyrenoidosa was investigated using three experimental techniques (artificial leaf, aqueous method, and O₂ electrode) to measure carbon assimilation. CO₂ response curves were determined under different O₂, pH, and temperature conditions. Regardless of the experimental technique and condition, O₂ inhibition was not evident until a concentration of 50% was reached; V_max values were reduced whereas K_m (CO₂) values were unaffected by the increasing O₂ concentration. The response of photosynthesis to O₂ was independent of CO₂ and HCO₃⁻ concentrations as well as temperature. Relative rates of photosynthesis showed a 4 to 5% stimulation in 2% O₂, a 12% inhibition in 50% O₂, and a 24% inhibition in 100% O₂. The inhibition by 50% O₂ was still reversible after 20 minutes exposure whereas 100% O₂ caused irreversible inhibition after only 4 minutes.     

Stability trends and fragmentation patterns of gaseous yttrium oxide clusters studied by fast atom bombardment tandem mass spectrometry

The fragmentation patterns of yttrium oxide cluster species YO⁺, Y₂O₂⁺, Y₂O₃⁺, Y₃O₄⁺, Y₄O₆⁺, Y₅O₇⁺, Y₆O₈⁺ and Y₇O₁₀⁺ were investigated at collision energies 30–110 and 170 eV by fast atom bombardment tandem mass spectrometry. The collision activated dissociation (CAD) spectra obtained revealed higher thermodynamic stability for the clusters of general formula Y_αO_(3α−1)/2⁺, where a is an odd number (e.g. YO⁺, Y₃O₄⁺, Y₅O₇⁺, Y₇O₁₀⁺) which are also the preferred CAD products for all oxide clusters studied. These most stable oxides are constituted by trivalent yttrium only whereas those containing formally tetravalent yttrium Y_aO_3a/2⁺, (where a is even) e.g. Y₂O₃⁺ and Y₄O₆⁺, are extremely unstable. The clusters Y_aO_(3a−2)/2⁺, (where a is even) containing divalent yttrium, e.g. Y₂O₂⁺ and Y₆O₈⁺, have considerable stability but their CAD products are again the thermodynamic products Y_aO_(3a−1)/2⁺. Electronic structures appear to have overriding significance in determining the thermo- dynamic stabilities of the oxide cluster species.     

Functional production of the Na+ F1FO ATP synthase from Acetobacterium woodii in Escherichia coli requires the native AtpI

The Na⁺ F₁F_O ATP synthase of the anaerobic, acetogenic bacterium Acetobacterium woodii has a unique F_OV_O hybrid rotor that contains nine copies of a F_O-like c subunit and one copy of a V_O-like c ₁ subunit with one ion binding site in four transmembrane helices whose cellular function is obscure. Since a genetic system to address the role of different c subunits is not available for this bacterium, we aimed at a heterologous expression system. Therefore, we cloned and expressed its Na⁺ F₁F_O ATP synthase operon in Escherichia coli. A Δatp mutant of E. coli produced a functional, membrane-bound Na⁺ F₁F_O ATP synthase that was purified in a single step after inserting a His₆-tag to its β subunit. The purified enzyme was competent in Na⁺ transport and contained the F_OV_O hybrid rotor in the same stoichiometry as in A. woodii. Deletion of the atpI gene from the A. woodii operon resulted in a loss of the c ring and a mis-assembled Na⁺ F₁F_O ATP synthase. AtpI from E. coli could not substitute AtpI from A. woodii. These data demonstrate for the first time a functional production of a F_OV_O hybrid rotor in E. coli and revealed that the native AtpI is required for assembly of the hybrid rotor.     

Noninvasive estimation of human tissue respiration with wavelet-analysis of oxygen saturation and blood flow oscillations in skin microvessels

Laser Doppler flowmetry, laser spectrophotometry of oxygen saturation, and the fluorescence determination of the NADH/FAD ratio were carried out in 30 subjects in the upper limb skin zones with and without arteriolovenular anastomoses (AVAs). It was demonstrated that the wavelet-analysis of oxygen saturation and blood flow oscillations in microvessels was an efficient approach to noninvasive estimation of the skin oxygen extraction (OE) and oxygen consumption (OC) rates. OE = (SaO₂ ? SvO₂)/SaO₂, where SaO₂ (%) and SvO₂ (%) are the oxygen saturations of arterial and venular blood, respectively. If the cardiac (A_c, perfusion units, p.u.) to respiratory rhythm amplitude (A_r, p.u.) ratio A_c/A_r ?? 1, SvO₂ = SO₂. If A_c/A_r > 1, SvO₂ = SO₂/(A_c/A_r). OC = M _nutr (SaO₂ ?? SvO₂) in p.u. · %O₂, where M _nutr is the nutritive blood flow value in p.u. M _nutr = M/SI, where SI is the shunting index of blood flow in microvessels. The perfusion, OE, and OC values were higher in the skin with AVAs than in the skin without AVAs. The perfusion and oxygen saturation values were more variable in the skin with AVAs. The oxygen diffusing from the tiniest arterioles and capillaries is the most important for tissue metabolism. The contribution of the total perfusion and the oxygen diffusion from arterioles to tissue metabolism increased under the tissue ischemia conditions.     

Transition metal derivatives of 1,10-phenanthroline-5,6-dione: Controlled growth of coordination polynuclear derivatives

The synthesis and the characterization of several mono- and polymetallic derivatives of 1,10-phenanthroline-5,6,-dione (1) are presented.The reaction of 1 with M(CO)₆ (M = Cr, Mo) gives compounds of general formula M(O,O′-C₁₂H₆N₂O₂)₃, M = Cr (2), Mo (3).Compound 3 is also obtained starting from Mo(η⁶-CH₃C₆H₅)₂, whereas the reaction of Cr(η⁶-CH₃C₆H₅)₂ with 1 affords the ionic derivative [Cr(η⁶-CH₃C₆H₅)₂][C₁₂H₆N₂O₂] (4), which has been studied by EPR spectroscopy and DFT calculations.FeCl₂(N,N′-C₁₂H₆N₂O₂)₂ (6), is obtained by thermal decomposition of [Fe(N,N′-C₁₂H₆N₂O₂)₃]Cl₂ (5).Polymetallic compounds of general formula Cr[O,O′-C₁₂H₆N₂O₂-N,N′-MCl₄]₃,containing chromium and a Group 4 element M = Ti (7), Zr (8), Hf (9), are prepared from Cr(O,O′-C₁₂H₆N₂O₂)₃ and the corresponding MCl₄ or MCl₄DME. Polynuclear derivatives of iron and chromium of formula [Fe(N,N′-C₁₂H₆N₂O₂-O,O′-CrCl₂(THF)₂)₃][PF₆]₂ (10), and Cr[O,O′-C₁₂H₆N₂O₂-N,N′-FeCl₂(THF)]₃ (11), are obtained by the reaction of [Fe(N,N′-C₁₂H₆N₂O₂)₃][PF₆]₂ with three equivalents of CrCl₂(THF)₂ and from Cr(O,O′-C₁₂H₆N₂O₂)₃ and FeCl₂(THF)_1.5, respectively. Compound 11 reacts with 1 (3 equivalents in sym-C₂H₂Cl₄ or 6 equivalents in ethanol) to give Cr[O,O′-C₁₂H₆N₂O₂-N,N′-FeCl₂(N,N′-C₁₂H₆N₂O₂)]₃ (12), and [Cr(O,O′-C₁₂H₆N₂O₂-N,N′-Fe(N,N′-C₁₂H₆N₂O₂)₂)₃]Cl₆ (13), respectively.     

基于树干液流技术的北京市刺槐冠层吸收臭氧特征研究

全球范围内加速的城市化导致空气质量严重退化。随着北京市建设范围不断扩大和机动汽车数量迅猛增长,空气污染日益严重。浓度不断增加的近地层臭氧作为影响全球气候变化的重要因素和危害人类健康、动植物生长的二次污染物,受到广泛关注。城市树木能够有效地去除大气污染物,进而提高空气质量。目前已有很多研究关于区域尺度上城市树木吸收臭氧,然而,冠层尺度上城市树木吸收臭氧特征少有研究。因此,本文基于树干液流技术,结合天气变化和大气臭氧浓度分析,研究夏秋季节北京市典型绿化树种刺槐（Robinia pseudoacacia）整树冠层吸收臭氧特征及环境影响因素。结果表明,在日尺度上,刺槐吸收臭氧速率变化呈单峰曲线,于下午15:00左右达到峰值;夏季峰值范围较宽,秋季峰值范围较窄;中午前后累积吸收臭氧量增加最明显。在季节尺度上,夏季刺槐吸收臭氧速率高于秋季;夏季累积吸收臭氧量显著增加,秋季略有增加。刺槐吸收臭氧的时间变化规律取决于大气臭氧浓度和冠层对臭氧的导度。臭氧浓度日变化和季节变化明显,导致刺槐吸收臭氧速率时间变化格局与之接近。在一定的臭氧浓度下,刺槐吸收臭氧速率的变化主要由冠层对臭氧的导度调控,进而受水汽压亏缺和总辐射的影响。随着水汽压亏缺降低,刺槐冠层对臭氧的导度明显下降;总辐射大于600 W/m2,冠层对臭氧的导度迅速下降。研究树种刺槐单位冠层投影面积上年吸收臭氧量约为0.16 g/m2,明显低于基于模型得到的结果,表明评估森林受臭氧危害的风险应考虑树种冠层臭氧通量。     

Acid activation of titanium alkoxide systems - Structural characterisation of Ti(IV) sulfonyl-imide complexes

Treatment of [Ti(OⁱPr)₄] with the sulfonyl-imine systems Tos₂NH ([(p-Me-C₆H₄SO₂)₂NH]) and Tf₂NH ([(CF₃SO₂)₂NH]) results in the formation of the new Lewis acidic titanium sulfonyl-imide complexes [Ti(OⁱPr)₂(O,O′-Tos₂N)₂] (1) and [Ti(OⁱPr)₂(HOⁱPr)₂(O-Tf₂N)₂] (2), respectively. The molecular structures of the complexes have been determined by single crystal X-ray diffraction. The reaction of [Ti(OⁱPr)₃(OAr)] (Ar = 2,6-di-tert-butyl-4-methyl phenyl) with Tf₂NH results in the formation of the dimeric complex [Ti(OⁱPr)₃(O,O′-Tf₂N)]₂ (3), which has also been structurally characterised. The ability of the complexes to catalyst the Friedel-Crafts acylation of anisole has also been assessed.     

Photosynthetic responses of Monarch birch seedlings to differing timings of free air ozone fumigation

To study the effects of different periods of ozone (O₃) fumigation on photosynthesis in leaves of the Monarch birch (Betula maximowicziana), we undertook free air O₃ fumigation to Monarch birch seedlings at a concentration of 60 nmol mol^?1 during daytime. Plants were exposed to O₃ at early, late or both periods in the growing season. The light-saturated net photosynthetic rate (A _sat) in July and August was reduced by O₃ exposure through a reduction in the maximum rate of carboxylation (V _c,max). In early September, on the other hand, despite a reduction in V _c,max, A _sat was not reduced by O₃ due to a counteracting increase in the stomatal conductance. Through the experiment, there was no difference in sensitivity to O₃ between maturing and matured leaves. We analyzed the relationship between A _sat, V _c,max and accumulated stomatal O₃ flux (AF_st). Whereas V _c,max decreased with increasing AF_st, the correlation between A _sat and AF_st was weak because the response of stomatal conductance to O₃ was affected by season. We conclude photosynthetic response of Monarch birch to O₃ exposure changes with season. This is due to the inconstant stomatal response to O₃ but not due to the respose of biochemical assimilation capacity in chloroplasts.     

Kinetics and Apparent K(m) of Oxygen Cycle under Conditions of Limiting Carbon Dioxide Fixation

A mass spectrometer with a membrane inlet was used to monitor light-driven O₂ evolution, O₂ uptake, and CO₂ uptake in suspensions of algae (Scenedesmus obliquus). We observed the following. (a) The rate of O₂ uptake, which, in the presence of iodoacetamide, replaces the uptake of CO₂, showed a distinct plateau (V_max) beyond ~30% O₂ and was half-maximal at ~8% O₂. We concluded that this light-driven O₂ uptake process, which does not involve carbon compounds, is saturated at lower O₂ concentrations than are photorespiration and glycolate formation. (b) In the absence of inhibitor, O₂ evolution was relatively unaffected by the presence or absence of CO₂. During the course of CO₂ depletion, electron flow to CO₂ was replaced by an equivalent flow to O₂. (c) There was a distinct delay between the cessation of CO₂ uptake and the increase in O₂ uptake. We ascribe this delay to the transient utilization of another electron acceptor—possibly bicarbonate or another bound form of CO₂.     

Ac4GlcNAcF3, an OGT-tolerated but OGA-resistant regulator for O-GlcNAcylation

O-Linked N-acetylglucosamine (O-GlcNAc) is an abundant posttranslational monosaccaride-modification found on Ser or Thr residues of intracellular proteins in most eukaryotes. The dynamic nature of O-GlcNAc has enabled researchers to modulate the stoichiometry of O-GlcNAc on proteins in order to investigate its function. Cell permeable small moleculars have proven invaluable tools to increase O-GlcNAc levels. Herein, using in vitro substrate screening, we identified GlcNAcF₃ as an OGT-accepted but OGA-resistant sugar mimic. Cellular experiments with cell-permeable peracetylated-GlcNAcF₃ (Ac₄GlcNAcF₃) displayed that Ac₄GlcNAcF₃ was a potent tool to increase O-GlcNAc levels in several cell lines. Further, NIH3T3 cells interfered with OGT (siOGT) showed significant decreasing of O-GlcNAc levels with Ac₄GlcNAcF₃ treatment, indicating O-GlcNAcF₃ was an OGT-dependent modification. In addition, cellular toxic assay confirmed O-GlcNAcF₃ production has no significant effect on cell proliferation or viability. Thus, Ac₄GlcNAcF₃ represents a safe and dual regulator for both OGT and OGA, which will benefit the study of O-GlcNAc.     

Novel gaseous polyatomic binary and ternary lanthanide oxides

A variety of novel gaseous polyatomic binary and ternary oxides were observed at ambient temperature arising from lanthanide (Ln) nitrate Schiff base complexes, simple salts and sesquioxides, in an FAB mass spectrometer. The new binary oxides (as singly positive ions) detected are Ln₂O₃, Ln₃O₃, Ln₃O₄, Ln₄O₄, Ln₄O₅, Ln₄O₆, Ln₅O₆, Ln₅O₇, Ln₅O₈, Ln₆O₈, Ln₆O₉, Ln₇O₁₀, Ln₈O₁₁, Ln₈O₁₂ and Ln₉O₁₃; the ternary gaseous oxides are CeEuO₂, CeEu₂O₃ and Ce₂EuO₄, LaYbO₂, La₂YbO₄ and LaYb₂O₄; NdHoO₃, Nd₂HoO₄, and NdHo₂O₄; YTmO₃; Y_xTm_3−xO₄, x=1−2; Y_xTm_4−xO₆, x=1−3; Y_xTm_5−xO₇, x=1−4; Y_xTm_6−xO₉, x=1−5. Some of these oxides show the lanthanide cations in unusual oxidation states. Gadolinium-gallium ternary oxides, GdGaO₂, GdGaO₃ and Gd₂GaO₄ were also detected. The FAB MS environment is significantly reducing, yielding a homologous series Eu_nO_n where Eu²⁺ is dominant (E°(Eu³⁺/Eu²⁺)=−0.35 V) and no gallium or indium oxides (E°(M³⁺/M°=−0.34 V (In), −0.53 V (Ga)) were formed. The stoichiometry of the polylanthanide ternary oxides formed is determined largely by the chemistry of the major metallic component. The gaseous polyatomic oxides are probably formed through a reductive condensation process involving primary species Ln⁺ and LnO⁺ formed when the rare earth compounds are struck by fast Xe atoms. The demonstrated possibility of double component oxide formation broadens the number and types of gaseous lanthanide oxides which are accessible.     

Macrophage-mediated cytolysis of erythrocytes in the guinea pig. II. Role of oxidative burst products in macrophage cytotoxicity activated by lectins and phorbol ester derivatives

Guinea pig peritoneal macrophages (GPPM) exhibited enhanced production of O₂^? and H₂O₂, and cytolytic activity toward erythrocytes, in response to reagents such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA), its methylated derivative 4-O-MeTPA, Con A, wheat germ agglutinin (WGA), and opsonized zymosan. In order to examine the possible role of oxidative burst products such as O₂^? and H₂O₂ in the cytolytic process, we used reagents and enzymes which influence the balance of O₂^? and H₂O₂ outside and inside the GPPM cells. Macrophage-mediated cytolysis (MMC) of erythrocytes in the presence of the activators and modulators was assessed by ⁵¹Cr release assay. MMC activated by TPA and 4-O-MeTPA was inhibited by scavengers of H₂O₂ such as catalase and α-tocopherol, and was augmented by the catalase inhibitor 3-amino-1,2,4-triazole, and by horseradish peroxidase. TPA- and 4-O-MeTPA-activated MMC was only partially inhibited by the O₂^? scavenger cytochrome c and the enzyme superoxide dismutase and unaffected by cytochalasin D (an inhibitor of phagocytosis). MMC activated by the lectins Con A and WGA was unaffected by the scavengers and enzymes used, but markedly inhibited by cytochalasin D. Activation of MMC by TPA, WGA, and phagocytosis of opsonized zymosan, as well as O₂^? and H₂O₂ generation triggered by these reagents, were markedly inhibited by chlorpromazine. The results indicate that GPPM-mediated cytolysis activated by lectins, phorbol ester derivatives, and phagocytosis of opsonized zymosan, is dependent on the generation of oxidative burst products, mainly H₂O₂. TPA- or 4-O-MeTPA-activated MMC is mainly an extracellular event, while lectin-activated MMC may take place within the macrophages.     

Response of the Microaerophilic Bifidobacterium Species, B. boum and B. thermophilum, to Oxygen

We investigated the effects of O₂ on Bifidobacterium species using liquid shaking cultures under various O₂ concentrations. Although most of the Bifidobacterium species we selected showed O₂ sensitivity, two species, B. boum and B. thermophilum, demonstrated microaerophilic profiles. The growth of B. bifidum and B. longum was inhibited under high-O₂ conditions accompanied by the accumulation of H₂O₂ in the medium, and growth was restored by adding catalase to the medium. B. boum and B. thermophilum grew well even under 20% O₂ conditions without H₂O₂ accumulation, and growth was stimulated compared to anoxic growth. H₂O-forming NADH oxidase activities were detected dominantly in cell extracts of B. boum and B. thermophilum under acidic reaction conditions (pH 5.0 to 6.0).     

Oxygen Inhibition of Photosynthesis: I. Temperature Dependence and Relation to O(2)/CO(2) Solubility Ratio

The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O₂ in the C₃ species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O₂/CO₂ in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O₂ and CO₂ in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O₂/CO₂ can be increased by increased leaf temperature under constant atmospheric levels of O₂ and CO₂ (since O₂ is relatively more soluble than CO₂ with increasing temperature); by increasing the relative levels of O₂/CO₂ in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O₂/CO₂ is kept constant, as leaf temperature is increased, by varying the levels of O₂ or CO₂ in the atmosphere, then the percentage inhibition of photosynthesis by O₂ is similar. The decreased solubility of CO₂ relative to O₂ (decreased CO₂/O₂ ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O₂ under atmospheric conditions with increasing temperature.     

The Mechanism of the Calorigenic Action of Thyroid Hormone : Stimulation of Na+ + K+-activated adenosinetriphosphatase activity

In an earlier study, we proposed that thyroid hormone stimulation of energy utilization by the Na⁺ pump mediates the calorigenic response. In this study, the effects of triiodothyronine (T₃) on total oxygen consumption (Q_OO2), the ouabain-sensitive oxygen consumption [Q_OO2(t)], and NaK-ATPase in liver, kidney, and cerebrum were measured. In liver, ~90% of the increase in Q_OO2 produced by T₃ in either thyroidectomized or euthyroid rats was attributable to the increase in Q_OO2(t). In kidney, the increase in Q_OO2(t) accounted for 29% of the increase in Q_OO2 in thyroidectomized and 46% of the increase in Q_OO2 in euthyroid rats. There was no demonstrable effect of T₃ in euthyroid rats on Q_OO2 or Q_OO2(t) of cerebral slices. The effects of T₃ on NaK-ATPase activity in homogenates were as follows: In liver +81% from euthyroid rats and +54% from hypothyroid rats. In kidney, +21% from euthyroid rats and +69% from hypothyroid rats. T₃ in euthyroid rats produced no significant changes in NaK-ATPase or Mg-ATPase activity of cerebral homogenates. Liver plasma membrane fractions showed a 69% increase in NaK-ATPase and no significant changes in either Mg-ATPase or 5'-nucleotidase activities after T₃ injection. These results indicate that thyroid hormones stimulate NaK-ATPase activity differentially. This effect may account, at least in part, for the calorigenic effects of these hormones.