Thresholds of cat cochlear nucleus neurons to microwave pulses

Action potentials of neurons in cat dorsal and posteroventral cochlear nuclei were recorded extracellularly with glass microelectrodes while the head of the cat was exposed to microwave pulses at 915 MHz using a diathermy applicator. Response thresholds to acoustic tones, acoustic clicks, and microwave pulses were determined for auditory units with characteristic frequencies (CFs) from 278 Hz to 39.2 kHz. Tests with pulsatile stimuli were performed for durations of 20-700 mus, principally 20, 70, and 200 mus. Brainstem midline specific absorption rate (SAR) threshold was as small as 11.1 mW/g per pulse, and specific absorption (SA) threshold was a small as 0.6 muJ/g per pulse. Microwave thresholds were generally lower for CF less than 9 kHz, as were most acoustic thresholds. However, microwave threshold was only weakly related to click threshold and CF-tone threshold of each unit.     

Three-dimensional reconstructions of nucleolus-organizing regions in PHA-stimulated human lymphocytes

Ultrastructure and three-dimensional distribution of nucleolus-organizing regions have been studied on ultrathin serial sections of PHA-stimulated human lymphocytes. During the 48 hr of activation the size of fibrillar centers (FCs) decreased from 0.6-0.9 microns to 0.2-0.3 microns and the number of FCs increased rapidly from one to 75-107 per cell. The number of fibrillar complexes (i.e. associations of a different number of FCs connected by the dense fibrillar component) also increased but did not reach the maximum number of nucleolar organizers presented here. Three-dimensional computer reconstructions of fibrillar complexes showed that lymphocyte activation was accompanied by early (2-4 hr) changes in the shape of the primary fibrillar center. Invagination of the dense fibrillar component on its surface occurred and division into two or more smaller FCs followed. Gradually, the typical structure of the nucleolus with several fibrillar complexes and many FCs was formed. These results confirm the hypothesis of fibrillar complex-nucleolar organizer correlation published recently.     

豚鼠听觉诱发电位中潜伏期反应Pa波起源的研究

将豚鼠大脑皮层划分为五个区,采用大脑皮层吸除破坏与海人酸局部浸润破坏相结合的方法,研究了MLR的起源以及皮层各区域与MLR的关系。结果表明,破坏听区以外各区域,对MLR影响不大,一旦破坏听区皮层,MLR主波Pa立即消失,并且不再恢复。海人酸局部浸润破坏不仅进一步证明Pa波来源于听区皮层,而且还表明Pa波主要来源于听区皮层内神经无电活动,与皮层下听觉中枢及其向听区皮层投射的纤维无关。     

Reconstitution of plastoquinone in the D1/D2/cytochrome b-559 photosystem II reaction centre complex

Reconstitution of plastoquinone in the photosystem II D1/D2/cytochrome b-559 reaction centre complex, in the presence of the detergent Triton X-100, is reported. Illumination of the reconstituted system results in the reduction of cytochrome b-559, the process being partly herbicide-sensitive. In addition, the reconstitution of plastoquinone results in the ability of the isolated reaction centre to catalyse the photoreduction of 2,6-dichlorophenolindophenol in the presence of the exogenous electron donor diphenylcarbazide.     

重复短声调频在豚鼠诱发的皮层慢反应及反应阈

重复短声调频在豚鼠诱发的皮层慢反应的基本特征与其他声刺激诱发者相似,它为一正负正三相波,第一正峰的潜伏期约50ms。以调频深度表示的反应阈△f_r较易测定,可以作为动物频率辨别能力的定量表达。对从250至4000pps的复频,豚鼠△fr的均值只在2.0至2.6pps间波动,因此对需要比较不同状况时△fr的变化,一般只取复频1000pps的△f_r便可代表,不必取整个△f_r曲线。听觉系统对重复短声的频率变化比纯音的容易检别,本文对可能的机理进行了讨论。     

An asymmetric dimer exciton model. Application to the primary electron donor of bacterial photoreaction center

An asymmetric dimer excition theory is developed that takes into account both environmental and vibronic effects on the electronic transition energies. Explicit equations are presented for the transition energies, the dipole moments, the angle between the dipole moments and the dipole and rotational strengths for the electronic transitions in this asymmetric dimer. This model is proposed to describe the structure of the special pair of bacteriochlorophyll a molecules believed to constitute the primary electron donor of bacterial photoreaction center. The model is found to be consistent with most of the spectroscopic properties of the photoreaction center. We used the equations derived from the asymmetric model along with absorption and circular dichroism spectroscopy data to predict a geometrical structure for the primary electron donor.     

Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. III. Chlorophyll fluorescence at 77 K

Photoinhibition in Lemna gibba L. was studied by interpreting chlorophyll fluorescence characteristics at 77 K on the basis of the bipartite model of Butler and co-workers (Butler 1978). Application of this analysis to chloroplasts (isolated from plants before and after exposure to a photosynthetic photon flux density of 1 750 μmol m⁻² s⁻¹ at 3°C for 2 h) revealed that photoinhibition had the following effect on primary events in photosynthesis. Firstly, the fluorescence of PS II increased (44%) in the state of open traps (F_o) and decreased (32%) in the state of closed traps (F_m). It is suggested, that the F_o-decrease reflects increased quenching by radiationless decay, both effects occurring at PS II reaction centers. Secondly, the rate constant for transfer of excitation energy from PS II to PS I (k_T(μ→J)) increased by 34%. However, in the state of closed traps, the flux of excitation energy via this transfer process decreased, most likely because of increased quenching by radiationless decay at PS II reaction centers. Thirdly, the probability for fluorescence from PS I decreased (19%). This indicates increased quenching by radiationless decay.     

Electrophysiological properties of cellular and paracellular conductive pathways of the rabbit cortical collecting duct

Summary Microelectrode techniques were applied to the rabbit isolated perfused cortical collecting duct to provide an initial quantitation and characterization of the cell membrane and tight junction conductances. Initial studies demonstrated that the fractional resistance (ratio of the resistance of the apical cell membrane to the sum of the resistances of the apical and basolateral membranes) was usually independent of the point along the tubule of microelectrode impalement—implicating little cell-to-cell coupling—supporting the application of quantitative techniques to the cortical collecting duct. It was demonstrated that in the presence of amiloride, either reduction in the luminal pH or the addition of barium to the perfusate selectively reduced the apical membrane potassium conductance. From the changes inG ^te and fractional resistance upon reducing the luminal pH or addition of barium to the perfusate, the transepithelial, apical membrane, basolateral membrane and tight junction conductances were estimated to be 9.3, 6.7, 8.1 and 6.0 mS cm^–2, respectively. Ninety to ninety-five percent of the apical membrane conductance reflected the barium-sensitive potassium conductance in the presence of amiloride with an estimated potassium permeability of 1.1×10^–4 cm sec^–1. Reduction in the perfusate pH to 4.0 caused a 70% decrease in the apical membrane potassium conductance, implying a blocking site with an acidic group having a pK _a near 4.4. It is concluded that both the transcellular and paracellular pathways of the cortical collecting tubule have high ionic conductances, and that the apical membrane conductance primarily reffects a high potassium conductance. Furthermore, both reduction in the perfusate pH and addition of barium to the perfusate selectively block the apical potassium channels, although the site of inhibition likely differs since the two ions display markedly different voltage-dependent blocks of the channel.     

Isolation, properties and tissue distribution of rat glutathione transferase E

Uptake of Li+ induced by the addition of proline to a cell suspension of Escherichia coli was detected using an Li+-selective electrode. This Li+ uptake was inhibited by L-azetidine 2-carboxylic acid, a competitive inhibitor of the proline transport system. Thus, direct evidence for Li+-proline cotransport via the proline transport system was obtained. Kinetic parameters of the Li+ uptake were determined.     

Damping of oscillations in the semiquinone absorption in reaction centers after successive flashes. Determination of the equilibrium between QA−QB and QAQB−

A quantitative model for the damping of oscillations of the semiquinone absorption after successive light flashes is presented. It is based on the equilibrium between the states Q_A^?Q_B and Q_AQ_B^?. A fit of the model to the experimental results obtained for reaction centers from Rhodopseudomonas sphaeroides gave a value of $\text{α =}\text{[}\text{Q}{}_{\mathrm{<mtext>A</mtext>}}{}^{\mathrm{?}}\text{Q}{}_{\mathrm{<mtext>B</mtext>}}\text{]}\text{([}\text{Q}{}_{\mathrm{<mtext>A</mtext>}}{}^{\mathrm{?}}\text{Q}{}_{\mathrm{<mtext>B</mtext>}}\text{] + [}\text{Q}{}_{\mathrm{<mtext>A</mtext>}}\text{Q}{}_{\mathrm{<mtext>B</mtext>}}{}^{\mathrm{?}}\text{])}\text{= 0.065 ± 0.005}$ (T = 21°C, pH 8).