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  • 1
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The response of thymic lymphocytes of the pig to phytohemagglutinin was studied with H3 thymidine in cultures, from 0-72 hours. At the beginning of the culture period 6-18% of lymphocytes were in DNA synthesis. during the first 24 hours a sharp decrease in the number of DNA synthesizing cells was observed in both pha and control cultures, although pha cultures consistently showed small but significantly greater numbers of DNA synthesizing cells. this was followed by a definite peak in DNA synthesis and mitotic response of a minority of the cells in pha cultures between 48-54 hours, whereas in control cultures activity ceased. in addition, a small proportion of the progeny of initially DNA synthesizing medium sized lymphocytes was apparently stimulated by pha and found in mitosis by 48 hours.It was concluded that the thymus contains a fraction of lymphocytes, not in the mitotic cycle, which are capable of being transformed by pha to mitotic activity. the data also suggests some stimulation of cells already in the mitotic cycle.
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  • 2
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The respiratory activity of avian blood cells was determined with samples of whole blood from individual male and female chickens. this oxygen consumption represents only that of the cells since no measurable activity was found in the plasma samples. the precision of determining respiratory activity was examined statistically and found to be approximately that obtained with a blood cell count but much less precise than the packed cell volume determination. the variability of cell count and mean corpuscular volume indicates that neither is a good means for expressing oxygen consumption - the most meaningful basis is oxygen consumption per milliliter of cells. the relationship between blood cell respiration and temperature is described.
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  • 3
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: By the “labeled mitoses” method of Quastler and Sherman and others, the cell cycle of the germinative zone cells of the bullfrog lens epithelium has been characterized. It has been shown that this cycle lasts approximately 83 days with the DNA synthetic phase enduring 100 hours and G2, 11 hours. G1 occupies over 90% of the total time. the duration of mitosis itself has not been precisely determined. the length of the synthetic phase was corroborated by double labeling with c14 and h3-thymidine.When the temperature is raised by 6°c, from 24° to 30° the cycle is compressed by 40%.When the nongerminative, central cells of bullfrog lens epithelium are activated (stimulated to undergo DNA synthesis and mitosis) by injury or through in vitro culture, the length of the cycle also appears to decrease. in the in vitro experiments the generation time, as judged by the period elapsing between two successive bursts of DNA synthesis involving the same cells, amounts to 177-190 hours at 24°c. by raising the temperature to 30°c the time from injury or isolation until the appearance of the first wave of mitosis is reduced by 20%.
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  • 4
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Low concentrations (below 0.00005 m) of colchicine and low intensities (below 2,800 psi) of pressure, applied separately to early prophase eggs (lytechinus variegatus) produced no measurable inhibition of the first cleavage division (at 20°c). in combination, however, these subliminal treatments produced marked inhibition. complete blockage, in fact, was observed: at 2,300 psi for eggs in 0.00004 m colchicine; at 2,500 psi for eggs in 0.00003 m; and at 2,800 psi for eggs in 0.00002 m solutions.The curves obtained by plotting percentage inhibition as a function of pressure for each of the colchicine concentrations specified above were approximately parallel to one another; but each decrement in the colchicine concentration shifted the curve about 300 psi higher along the (pressure) abscissa.In short, a distinct synergism was found in reference to the anti-mitotic effects of colchicine and pressure. This result is quite opposite to that reported previously in regard to the actions of heavy water and high pressure.As to basic mechanism, the evidence indicates that both colchicine and pressure exert their effects by inhibiting polymerization of the subunits of a fibrous protein which constitutes an important structural component of the mitotic apparatus or by depolymerizing the mitotic protein, if it already has been formed at the time of treatment.
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  • 5
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The responses of single units and evoked potentials to a pair of artificial sounds, mimicking theorientation sound and echo, and to tape recorded actual orientation sounds were studied in terms of recovery cycle. the recovery cycle of single units could be classified into four groups: (1) short suppression (4%), (2) delayed inhibition (11%), (3) temporal recovery with or without a supernormal phase (7%), and (4) undelayed inhibition (78%) lasting 4 to 26 msec. therefore the majority of neurons were not excited by the second sound (echo) of a pair when it was delivered within several milliseconds after the first (out-going orientation sound). the duration of the recovery cycle was a function of the intensity of a pair of sounds. the weaker the first tone pulse relative to the second, the more rapid the recovery to the second. therefore, the reception of echoes is probably improved by contraction of middle ear muscles resulting in attenuation of self-stimulation by the out-going pulse.The collicular evoked potential consisted of two components, a fast one mainly due to the incoming fibers from lower levels and a slow one due to the main body of the inferior colliculus. The slow component showed slow recovery cycles as did the majority of single units while the fast one recovered very quickly. No noticeable difference in recovery cycles was found between awake and anesthetized animals. The functional meaning of inhibitory periods in the recovery cycle and role of the inferior colliculus in echo-location are discussed.
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  • 6
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: When a weak electric field is applied to longitudinal sections of myelinated nerve, myelin material migrates out of the tissue edges towards both poles. the materials migrating from the anodal and cathodal edges seem to be chemically similar but differ in physical properties. at the anodal edge the bimolecular lipid layers rearrange into spherical micelles forming an “oil in water” emulsion, and at the cathodal edge into micelles forming a “water in oil” emulsion. the latter is unstable in water and is rapidly transformed into an “oil in water” emulsion. these findings have physiological and structural implications for the study of biological membranes.
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  • 7
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Metabolic control reactions have been studied in the intact toad bladder by means of fluorescence spectrophotometric measurement of reduced pyridine nucleotide and by measurement of respiration with the platinum electrode. substrates such as pyruvate and succinate lead to prompt increases in reduction level of pyridine nucleotide with only slight acceleration of respiration. major metabolic control is exerted by adp, which depletes the intact bladder of reduced pyridine nucleotide and accelerates respiration. respiratory control ratios, as for isolated mitochondria, depend upon the substrate being metabolized. a significant fraction of added adp appears to gain entry into the intact toad bladder and is converted to atp, anaerobiosis and amobarbital lead to increased levels of reduction of pyridine nucleotide. the spectroscopic and metabolic properties of the reduced pyridine nucleotide being studied identify it with that fraction of dpnh which is bound at one of the energy conservation sites linking phosphorylation reactions with electron transfer.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 67 (1966), S. 355-360 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The water exchange has been measured in oocytes of siredon mexicanum and rana temporaria, and in unfertilized eggs and early gastrulae of the former species, by recording the D2O—H2O exchange with the cartesian diver balance.In oocytes, where no diffusion barrier to water is demonstrable, the temperature coefficient Q10 for the exchange of water is about 1.3-1.4, corresponding to that of free diffusion. in unfertilized eggs, and in early gastrulae the exchange is considerably slowed down, indicating that a surface membrane to some extent limits the rate of exchange. at the same time the Q10 value is increased, lying in the range 2.3-3.8. since it is most likely that the exchange even in this case occurs by diffusion, but through membrane pores, it is concluded that the area available for diffusion (pore size or number, or both) increases with temperature.
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  • 9
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The rate of C14O2 incorporation into amino acids and organic acids in C. reinhardtii is a function of particular stages of development in the life cycle of the alga. Gametic differentiation in nitrogen free medium is accompanied by a reduced rate of amino acid synthesis and a higher synthesis of organic acids than that found for the cells undergoing vegetative development. The addition of ammonium to differentiating gametes results in an increased synthesis of amino acids, particularly the basic ones, and a concomitant reduction in organic acid synthesis.
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  • 10
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Electropotential differences between the cell interior and the external medium have been studied with intracellular microelectrodes in ovarian oocytes, ovulated unfertilized eggs and fertilized eggs of R. pipiens. In ovarian oocytes the cytoplasm was 50 to 80 mV negative, relative to isotonic Ringer's solution. In contrast, electrode penetration of the oocyte nucleus in situ indicated that the nucleoplasm was about 25 mV positive, relative to the cytoplasm. After ovulation, the cortical cytoplasm became 20 to 50 mV positive with regard to an external solution of 0.1 strength Ringer's solution (ca. pond water). Penetration of the cytoplasm at levels from 0.3 to 0.6 mm below the egg surface revealed an inner zone with a potential which was about 15 mV negative, relative to the cortical cytoplasm. A slow hyperpolarization of the cortical membrane occurred at activation, with the potential returning to that of the ovulated unfertilized egg within ten minutes. After fertilization, the egg cytoplasm remained positive until the first cleavage. As division proceeded, the cytoplasm slowly depolarized and became 50 to 60 mV negative, relative to 0.1 strength Ringer's solution.
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