镉对大鼠心肌细胞毒作用的实验研究

本文用组织化学、电镜、能谱分析及血镉测定等方法研究了低浓度镉对大鼠心肌细胞的毒作用。大鼠经饲料染镉12周,血镉浓度达5.42±0.65μg/L(对照组为1.01±0.38μg/L)。染镉组大鼠心肌细胞出现镉的频谱峰,LDH活性下降,但SDH活性增强,图像分析显示该两种酶活性的改变皆与各自的对照组差异有非常显著性意义(P<0.001)。肌球蛋白ATP酶活性也较对照组有所下降。电镜下,染镉大鼠心肌细胞部分肌节变短,肌丝紊乱、断裂、密度降低,失去A及I带的排列规则,Z盘增宽。线粒体成堆地聚集在肌丝区之间或肌膜下,部分出现肿胀、嵴断裂、甚至变成含有絮状物的大泡。以上结果提示低浓度镉对大鼠心肌细胞有毒作用。     

Phototaxis and Thermotaxis in Some Species of Amphistegina (Foraminifera)*

Positive phototaxis was demonstrated in specimens of Amphistegina radiata within the range of photonic fluxes of 10¹¹ to 10¹⁵ photons × cm^-2× sec^-1. No response was found at lower intensities. Amphistegina radiata has a Dartnall nomogram-shaped action spectrum with a peak at ～500 nm. In addition, A. radiata and A. madagascariensis, which had been maintained at 18 C, moved toward higher temperatures in a horizontal temperature gradient in total darkness. Amphistegina radiata and A. madagascariensis did not move at temperatures ≤ 12 C and ≤ 16 C respectively. An equal number of specimens moved toward the higher and lower temperatures in the gradient when A. radiata was placed at ～29 C and A. madagascariensis at ～22 C. The roles of light and temperature in the distribution of the genus Amphistegina in nature are discussed.     

Optical characterization of Photosystem II electron donors

Detailed absorbance difference spectra are reported for the Photosystem II acceptor Q, the secondary donor Z, and the donor involved in photosynthetic oxygen evolution which we call M. The spectra of Z and Q could be resolved by analysis of flash-induced kinetics of prompt and delayed fluorescence, EPR signal II_f and absorbance changes in Tris-washed system II preparations in the presence of ferricyanide and 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU). The spectrum of Z oxidation consists mainly of positive bands at 260, 300 and 390–450 nm on which a chlorophyll a band shift around 438 nm is superimposed, and is largely pH-independent as is also the case for the spectrum of Q reduction. The re-reduction of Z⁺ occurred in the millisecond time range, and could be explained by a competition between back reaction with Q^? (120 ms at pH 6.0) and reduction by ferrocyanide. When the Tris treatment is omitted the preparations evolve oxygen, and the photoreduction of Q (with DCMU present) is accompanied by the oxidation of M. The Q spectrum being known, the spectrum of the oxidation of M could be determined as well. It consists of a broad, asymmetric increase peaking near 305 nm and of a Chl a band shift, which is about the same as that accompanying Z in Tris-washed system II. Comparison with spectra of model compounds suggests that Z is a bound plastoquinol which is oxidized to the semiquinone cation and that the oxidation of M is an Mn(III) → Mn(IV) transition.     

Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Phototaxis of the unicellular red alga Porphyridium cruentum was studied by staining the slime tracks of individual cells as well as with the aid of a population method. Because of the increased straightness of the movement the mean linear velocity of a unilaterally illuminated population exceeds considerably that of an only photokinetically stimulated one. In white light the phototactic reaction is saturated already at 100 lx. The zero threshold lies at about 1 lx. Spectral sensitivity curves of phototaxis obtained at high photon fluence rates (>=10^–11 mol cm^–2 s^–1) display two main peaks which shift against each other at intermediate irradiances and, finally, form a single maximum in the blue range (443 nm) at low photon fluence rates (10^–12 and 10^–13 mol cm^–2 s^–1). Photon fluence rate-response curves reveal that supraoptimal irradiances decrease the phototactic reaction, especially in the range of the highest sensitivity of the cells. The action spectrum of phototaxis was calculated on the basis of the photon fluence rate-response curves. It shows a maximum at 443 nm and shoulder at 416 nm and between 467 and 477 nm. Wavelengths longer than 540 nm are phototactically inactive even at very high irradiances (25 W m^–2). Thus, this is the first phototactic action spectrum of a biliprotein-containing organism which does not indicate the participation of biliproteins in the absorption of phototactically active light. DCMU and potassium iodide have no specific effects on phototaxis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Photophobic reactions of the red alga Porphyridium cruentum have been studied by single cell observations and by population experiments with the light trap method. In white light traps photoaccumulation is saturated at about 6000 lx. Experiments with monochromatic light demonstrate the necessity of carefully separating the three basic light reactions, viz. phototaxis, photokinesis and photophobic response by an appropriate experimental set-up: In single-beam experiments trap wavelengths >695 nm cause photodispersal which is not due to photophobic entrance reactions, but is exclusively due to the positive photokinetic effect of the trap light. This photodispersal can be cancelled by a photokinetically active background light. In the short wavelength range not only photokinesis, but also phototaxis interferes with photophobic reactions thus affecting the density of photoaccumulations in the light trap. Phototactic and photokinetic interference can be avoided by a blue background light. The action spectrum measured this way indicates activity of photosystem I and photosystem II pigments in the perception of the step-down photophobic stimulus. Varying the wavelength of the background light at constant trap light absorbed mainly by photosystem I or photosystem II respectively, efficient spill-over of light energy from photosystem II to the light reaction of photosystem I could be demonstrated. From the results it is concluded that phobic reactions are induced by a decrease of the electron flow rate in the linear electron transport chain.     

Photoresponses of Chaoborus larvae

The diel vertical migration of Chaoborus larvae is a well known phenomenon. In order to quantify the ability of larvae to utilize underwater light cues in their migration, we measured photoresponses of fourth-instar Chaoborus punctipennis larvae in the laboratory. The action spectrum for these larvae was characterized by a maximum in sensitivity at 400 nm, a plateau at a lower sensitivity from 480 to 560 nm, and a region of much lower sensitivity at wavelengths longer than 620 nm. Dark-adapted larvae exhibited a positive phototaxis at low light intensity which shifted to a negative phototaxix as light intensity increased. At 540 nm the threshold intensity was 1.5 × 10^?9 W/m² for positive phototaxis and about 10^?6 W/m² for negative phototaxis. Light adaptation decreased sensitivity and altered the phototactic pattern. Larvae have a clear circadian rhythm in negative phototaxis, in which greatest responsiveness occurs early in the day. We suggest that the rhythm in photoresponsiveness primarily controls the timing of the downward migration at dawn.     

Light-dependent pH changes in leaves of C3 plants

Action spectra in the red region of the spectrum for light-dependent cytosolic alkalization in leaves of C₃ plants which also received a low background of blue light differed from the action spectra for light-dependent vacuolar acidification. Light above 680 nm was less effective in supporting the cytosolic alkalization reaction than light below 680 nm. In contrast, in leaves illuminated in CO₂-free air the light-dependent vacuolar acidification exhibited a maximum at or even above 700 nm. When photorespiratory carbohydrate oxidation was suppressed in low oxygen, a substantially changed action spectrum of the acidification reaction resembled in shape that of the cytosolic alkalization with the exception that it was extended towards the far-red. From the presented data and from previously published data (Yin et al., 1990b, Planta 182, 253–261; Yin et al., 1990c, Planta 182, 262–269) it is concluded that in the presence of a weak background of blue light, and in the absence of CO₂ which drains electrons from the electron transport chain, cyclic photophosphorylation induced by far-red light permits increased export of dihydroxyacetone phosphate from the chloroplasts into the cytosol where its oxidation increases the cytosolic energy state giving rise to increased proton transport across the tonoplast. The data do not lend support to the view that export of malate from the chloroplasts and its oxidation in the mitochondria contribute significantly to cytosolic energization in the light.Abbreviations CDCF 5-(and-6)-carboxy-2,7-dichlorofluorescein - DHAP dihydroxyacetone phosphate - OAA oxaloacetate - PGA phosphoglycerate This work was performed within the Sonderforschungsbereiche 176 and 251 of the University of Würzburg. Z.-H. Y. acknowledges support by the Leibniz program of the Deutsche Forschungs-gemeinschaft.     

Weak chemiluminescence of bilirubin and its stimulation by aldehydes

Bilirubin in an alkaline solution exhibits a weak chemiluminescence (CL) under aerobic conditions. This spontaneous CL was markedly enhanced by the addition of various aldehydes. The fluorescent emission spectrum of bilirubin, excited by weak intensity light at 350 nm, coincided with its CL emission spectrum (peak at 670 nm). CL emission from bilirubin was not quenched by active oxygen scavengers. This suggests that triplet oxygen reacts with bilirubin, and forms an oxygenated intermediate (hydroperoxide) as a primary emitter (oxidative scission of tetrapyrrole bonds in bilirubin is not involved in this CL). The Ehrlich reaction (test for monopyrroles) and hydrolsulphite reaction (test for dipyroles) on the CL reaction mixture and unreacted bilirubin showed no differences. When the CL was initiated by singlet oxygen, rather than superoxide anion, monopyrrole, was detected in the reaction products by gel chromatography. The inhibitory effect of a scavenger of singlet oxygen on CL was eliminated in the presence of formaldehyde. Therefore, triplet carbonyl, formed by singlet oxygen through the dioxetane structure in bilirubin, is not an emitter. The reaction mechanism of bilirubin CL and the formation of a hydroperoxide intermediate is discussed in relation to the chemical structure of luciferin molecules from bioluminescent organisms.     

Frequency characteristics of signals and instrumentation: Implication for EMG biofeedback studies

Signals can be analyzed in either the time or frequency domain. In the time domain, the analysis consists of manipulating and measuring one or more characteristics of the signal that may vary with time. One can, for instance, rectify a signal, filter it, calculate its mean value, display the histogram of its amplitude, and so forth. Frequency analysis is less well understood because it requires a lengthy mathematical treatment most easily done by computer. However, it gives exclusive information on a signal. For instance, when the frequency content of a signal is known, it is easy to specify which characteristics an amplifier must have in order to amplify the signal without distortion, or to set the cutoff frequencies of filters to eliminate noise. Also, in many circumstances, frequency spectra are more easily interpreted than the original raw data. Such is the case with the EMG where the random aspect of the signal makes some form of processing (i.e., rectification, filtering, etc.) necessary, but not always as meaningful as we would like. Thus we present here the principal characteristics of frequency analysis, and discuss its usefulness in analyzing EMG signals and its application to biofeedback, clinical practice, and research.The authors acknowledge the technical assistance of F. Kemp, M. Goyette, and C. Goulet. T. Milner kindly reviewed the final version of the text. The preparation of this paper was supported through funds from Health and Welfare Canada (NHRDP) and the Centre de recherche, Institut de réadaptation de Montréal.