LOCAL REDUCTION OF SPINDLE FIBER BIREFRINGENCE IN LIVING NEPHROTOMA SUTURALIS (LOEW) SPERMATOCYTES INDUCED BY ULTRAVIOLET MICROBEAM IRRADIATION

Irradiation of the mitotic spindle in living Nephrotoma suturalis (Loew) spermatocytes with an ultraviolet microbeam of controlled dose produced a localized area of reduced birefringence in the spindle fibers. The birefringence was reduced only at the site irradiated, and only on the spindle fibers irradiated. Areas of reduced birefringence, whether produced during metaphase or during anaphase, immediately began to move toward the pole in the direction of the chromosomal fiber, even though the associated chromosomes did not necessarily move poleward. Both the poleward and the chromosomal sides of the area of reduced birefringence on each chromosomal fiber moved poleward with about the same, constant, velocity. On the average, the areas of reduced birefringence moved poleward with about the same velocities as did the chromosomes during anaphase. The area of reduced birefringence was interpreted as a region in which most, though not necessarily all, of the previously oriented material was disoriented by the irradiation. The poleward movement of the areas of reduced birefringence indicates that the spindle fibers are not static, nonchangeable structures. The poleward movement possibly represents the manner in which the birefringent spindle fibers normally become organized. All the experiments reported were on primary spermatocytes which completed the second meiotic division subsequent to the experimentation. Since both the irradiated and the control cells completed the two meiotic divisions, the movement and irradiation effects studied in the first division were nondegenerative.     

He—Ne激光微束显微照射杂交水稻活体单细胞研究

利用激光微束显微照射水稻活体单细胞,经两年培养已获得一植株,收获种子350粒。     

ULTRAVIOLET IRRADIATION AND PIGMENT CELL IDIOBLASTS IN SPIRODELA OLIGORHIZA (LEMNACEAE)

In Spirodela oligorhiza and Wolffia punctata ultraviolet energy induces the conversion of colorless flavans present in scattered idioblasts to red-brown phlobaphene-like compounds. The rare appearance of pigment cells in laboratory grown material is discussed.     

DISTURBANCES IN THE DEVELOPMENT OF SMALL COLONIES FOLLOWING THE IRRADIATION OF DIFFERENT PARTS OF SINGLE CELLS IN TISSUE CULTURE WITH A HETEROCHROMATIC MICROBEAM OF ULTRAVIOLET LIGHT

Various sites in mouse L cells have been irradiated using an heterochromatic ultraviolet microbeam 3.5 μ in diameter, and the subsequent growth of the cells has been studied for 5–7 days after irradiation. Modifications in the growth curves were recorded for the total number of cells in each radiation category and significant anomalies in the DNA metabolism of some of the progeny of irradiated cells were noted at the end of the post-irradiaton incubation period. The frequency with which binucleate and giant cells were produced was also recorded and the results analysed. For equivalent absorbed doses, the nucleus is more sensitive than the cytoplasm in experiments of this type and there was some evidence to suggest that the maximum sensitivity is achieved when some nucleolar material is irradiated.     

SPHEROSOMES AND MITOCHONDRIA IN THE LIVING FUNGAL CELL

Study of living hyphae of Fusarium oxysporum Schlect., Fomes annosus (Fries) Cooke, Ceratocystis fagacearum (Bretz) Hunt, Basidiobolus ranarum Eidam, and Mycotypha microspora Fenner with phase contrast revealed that these fungi have spherosomes similar to those in vascular plants. The spherosomes are conspicuous in the hyphal tip, suggesting some function other than fat synthesis. It may be that the Woronin bodies reported by other workers are spherosomes. Mitochondria in these fungi are highly pleomorphic and exhibit saltatory movement. They often interact with nuclei in a manner suggesting close membrane contact.     

PROTECTIVE ACTION IN IRRADIATION OF AMYLASE SOLUTIONS WITH ULTRAVIOLET LIGHT

Evidence has been presented which indicates that the protective action of dogs'' sera in irradiation of pancreatin solutions with ultraviolet light is the result of a competitive absorption (screening action). A similar effect is found in simple pancreatin solutions for which we may account (at least to a first approximation) on the basis of assumed homogeneous absorption by a strong competitor in the solution for the radiations having inactivating power. These observations are of interest in connection with the theory of what has been called negative catalysis, especially in view of the marked effects of small quantities of the protecting substances.     

ANALYSIS OF MUSCLE CONTRACTION BY ULTRAVIOLET MICROBEAM DISRUPTION OF SARCOMERE STRUCTURE

In an effort to differentiate between the sliding filament theory for muscle contraction and alternative views which propose attachment between actin and myosin filaments at or across the H zone, rabbit psoas myofibrils were irradiated in various areas of the sarcomere with an ultraviolet microbeam. Irradiation of the I band appears to destroy the actin filaments; in vitro irradiation of F actin causes an irreversible depolymerization of the protein. Irradiation of the A band disorients the myosin but causes no apparent loss of dry mass. These effects are maximal at the wavelength of maximum absorption of the proteins involved. Actin filaments, released at the Z line of a sarcomere, are seen to slide into the A band on addition of ATP. Irradiation of a full A band prevents contraction, whereas irradiation of two-thirds of the A band, leaving a lateral edge intact, permits contraction at the non-irradiated edge. Thus contraction can occur in what is in essence only one-third of a sarcomere, eliminating any necessity for postulated H zone connections. These observations are in complete accord with the classical sliding filament theory but incompatible with either the contralateral filament hypothesis or the actin folding model for muscle contraction.     

JUNCTIONS BETWEEN INTIMATELY APPOSED CELL MEMBRANES IN THE VERTEBRATE BRAIN

Certain junctions between ependymal cells, between astrocytes, and between some electrically coupled neurons have heretofore been regarded as tight, pentalaminar occlusions of the intercellular cleft. These junctions are now redefined in terms of their configuration after treatment of brain tissue in uranyl acetate before dehydration. Instead of a median dense lamina, they are bisected by a median gap 20–30 A wide which is continuous with the rest of the interspace. The patency of these "gap junctions" is further demonstrated by the penetration of horseradish peroxidase or lanthanum into the median gap, the latter tracer delineating there a polygonal substructure. However, either tracer can circumvent gap junctions because they are plaque-shaped rather than complete, circumferential belts. Tight junctions, which retain a pentalaminar appearance after uranyl acetate block treatment, are restricted primarily to the endothelium of parenchymal capillaries and the epithelium of the choroid plexus. They form rows of extensive, overlapping occlusions of the interspace and are neither circumvented nor penetrated by peroxidase and lanthanum. These junctions are morphologically distinguishable from the "labile" pentalaminar appositions which appear or disappear according to the preparative method and which do not interfere with the intercellular movement of tracers. Therefore, the interspaces of the brain are generally patent, allowing intercellular movement of colloidal materials. Endothelial and epithelial tight junctions occlude the interspaces between blood and parenchyma or cerebral ventricles, thereby constituting a structural basis for the blood-brain and blood-cerebrospinal fluid barriers.     

一种新型的激光微束细胞打孔仪系统

研究成一种高性能的激光微束细胞打孔仪。YAG腔外倍频激光经空间滤波器、聚焦物镜作用于细胞,产生小于1μ的打孔直径,一个高倍率(约2000~X)电视监测系统作为细胞打孔及观测用;设计了一种长工作距(c′≥15mm),短焦距(f_o=6.25mm)的特殊聚焦物镜。     

A CELL KINETIC MODEL TO EXPLAIN THE TIME OF APPEARANCE OF SKIN REACTION AFTER X-RAYS OR ULTRAVIOLET LIGHT IRRADIATION

Skin reactions to various doses of X-rays (300 and 10 kV) and ultraviolet light (u.v.) have been compared using hairless mice. Two regions of epidermis with widely differing cell kinetics and gross structure have been compared. Little evidence could be found to support the idea that the early phases of the reaction are dependent on cell cycle time. The data can be explained by a model based on the assumption that epidermis contains only a small fraction of clonogenic (stem) cells and this fraction may vary in different epidermal regions. X-rays appear to exert their greatest destructive action on these clonogenic cells while u.v. is more indiscriminate in its action, killing both clonogenic and non-clonogenic cells.     

神经细胞膜钠通道的门控电流和门控动力学

根据作者已提出的神经轴突钠离子通道蛋白质分子构象模型,组成通道闸门的极性氨基酸侧链可以有两种类型:偶极子和荷电离子基团.它们在两种构象间的跃迁导致通道呈现关闭或开放态,并产生了门控电流相应的两种组分.对两种侧链跃迁动力学参量的计算结果表明,门控电流曲线的时间常数、稳态开启几率及门控电荷随膜电位的变化是不同的.去极化脉冲引起通道状态的变化,可由关闭态经过活化态转变为失活态,也可由关闭态经部分关闭态转变为失活态,对不同膜电位条件下一个通道各种稳定状态几率的计算表明,活化和失活的耦联程度随膜电位而改变.     

RENEWAL OF FATTY ACIDS IN THE MEMBRANES OF VISUAL CELL OUTER SEGMENTS

The renewal of fatty acids in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids. Most of the radioactive material could be extracted from the retina with chloroform-methanol, indicating that the fatty acids had been esterified in lipids. Analysis of the extracts, after injection of [³H]palmitic acid, revealed that the radioactivity was predominantly in phospholipid. Palmitic acid was initially concentrated in the pigment epithelium, particularly in oil droplets which are storage sites for vitamin A esterified with fatty acid. The cytoplasm, but not the nucleus of these cells, was also heavily labeled. Radioactive fatty acid was bound immediately to the visual cell outer segment membranes, including detached rod membranes which had been phagocytized by the pigment epithelium. This is believed to be due to fatty acid exchange in phospholipid molecules already situated in the membranes. Gradually, the concentration of radioactive material in the visual cell outer segment membranes increased, apparently as a result of the addition of new phospholipid molecules, possibly augmented by the transfer from the pigment epithelium of esterified vitamin A. Injected fatty acid became particularly concentrated in new membranes which are continually assembled at the base of rod outer segments. This localized concentration was short-lived, apparently due to the rapid renewal of fatty acid. The results support the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement, including fatty acid exchange and replacement of phospholipid molecules in existing membranes.     

LACK OF PHOSPHOLIPID TRANSPORT MECHANISMS IN CELL MEMBRANES OF THE CNS1

The possible transport role of phospholipid-protein complexes, present in the cell supernatant of rat brain was investigated using labelled choline as precursor of phosphatidyl choline. Results obtained after the intracranial injection of choline gave no indication of a sequence of events compatible with a transport of phospholipid molecules from the possible site of synthesis (microsomes) to the supernatant and subsequently to myelin. Chase experiments using rat brain slices incubated in vitro with radioactive choline agreed well with the above mentioned results. Contrariwise, when Na³⁵₂SO₄ was used as precursor, the results clearly indicated that synthesis of sulphatides takes place in microsomes, followed by transfer of the radioactive lipid to sulphatide-containing lipoproteins in the supernatant and finally to myelin. Results presented in this paper seem to give further support to the idea that other subcellular fractions, besides microsomes, can autonomously synthesize part of their own provision of phospholipids. Possible reasons which might explain the marked differences between the mechanisms of addition of phospholipids and sulphatides to myelin are discussed in relation to results obtained by other investigators.     

MICRURGICAL STUDIES IN CELL PHYSIOLOGY : VI. CALCIUM IONS IN LIVING PROTOPLASM.

The quiescence, rounding, sinking of the granules, and paling of the nucleus are similar to the effects seen after the injection of potassium and sodium chloride (11). Since the sodium salts of the anions were used, it might be inferred that the sodium is the active agent in the injected solutions. This is not entirely the case, however, for the effective concentrations of NaCl required are many times greater than those required in the case of the sodium salts of the calcium-precipitating anions. The fact that practically the same effects can be obtained in both cases leads one to suspect that there is a relation between the results of an increase in sodium ions and a decrease in calcium ions. It has been shown that a M/416 CaCl₂ solution will antagonize a M/1 NaCl solution and even a more concentrated solution of KCl inside the ameba (12). Therefore the reduction in amount of calcium may leave a comparatively high concentration of unantagonized sodium and potassium. The fine, purplish red granules resulting from the injection of the alizarin are, no doubt, the insoluble calcium alizarinate. Recovery of an ameba from such an injection may be explained by the postulate that the free calcium ions in the living ameba are in equilibrium with a reserve supply of unionized calcium. The equilibrium is upset when the free calcium is removed by precipitation or by other means, and the system may possibly react in such a way as to counteract the effect of the change imposed. By mobilization of the calcium from a reserve supply the ameba can therefore gradually resume its normal activity. The time required for the recovery depends on the amount of alizarin injected. The diffuse red color which is seen immediately following the injection of alizarin probably represents that extra amount of dye which was not used in precipitating the immediately available calcium. Then, as the calcium is being liberated from the reserve, it is taken up by this surplus alizarin, resulting in a gradual loss of the diffuse coloration and an increase in the number of purplish See PDF for Structure red calcium alizarinate granules. Only when all of the injected dye has been precipitated can the mobilized calcium be used to carry on the normal physiological processes of the organism. The need of calcium to effect ameboid movement has been shown by Pantin (13) in a series of immersion experiments. This fact is quite suggestive, because the first effect of the injection of any of the calcium precipitants is absolute quiescence. Furthermore, there is no return to normal movement until the calcium apparently becomes available to the protoplasm. In support of the conception of a reserve supply of calcium is the presence of the large crystals which give a positive reaction with alizarin for calcium on the death of the ameba. Schewiakoff (14), from crystallographic studies, claims that they are calcium phosphate. The effect of the injection of the calcium-precipitating anions on the calcium of the protoplasm may be shown in another way. In determining the relative toxicity of these salts an arbitrarily standardized injection, about one-fourth of the volume of an ameba, was used. This was introduced because of the necessity to avoid effects due to variable amounts of the solvent, viz., water.. Thus the water effect was kept constant, and the variations in actual amount of salt injected were obtained by using a graded series of concentrations. Arranging the sodium salts of these anions in order of increasing toxicity in one column, and the in vitro solubility products of the corresponding calcium salts in another column, it is seen that as the toxicity increases, the solubility product decreases (Table 1). This fact strongly suggests that the toxicity depends on the ability of the salt to remove calcium ions from the protoplasm. The apparent deviation of the carbonate from the rule can be explained by the specific effect of 002 (10) which is always present from the hydrolysis of the carbonate.     

紫外照射神经酰胺的生成及神经酰胺引起的细胞凋亡

参照文献报道的方法建立了测定细胞神经酰胺的激酶催化法,以该法所做的标准曲线在一定浓度范围内有很好的线性关系。以ＵＶＢ照射ＮＩＨ ３Ｔ３细胞,可以使细胞神经酰胺的水平在１分钟之内迅速升高１．５倍以上,基本上达到了细胞所能生成神经酰胺的最高峰值。可细胞膜的外源性神经酰胺（Ｃ２－ｃｅｒａｍｉｄｅ）作用于ＮＩＨ ３Ｔ３细胞后能够导致细胞的凋亡和坏死,其凋亡率在一定剂量范围内随神经酰胺浓度的增加而增加;而在