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61.
In an effort to determine empirically the proper age for separation of pigtailed macaque (Macaca nemestrina ) infants from their dams in a large domestic breeding colony, we conducted a retrospective survey of 1,592 infants. Survivorship was highest for infants not separated from their dams at all and for those separated within the first four months of life. Survivorship was poor for animals separated during or after the fifth month. Thus, not weaning or weaning early are the most acceptable management strategies in terms of mortality risk. This result is paradoxical with regard to nutritional considerations, but appears to be related to a sensitive period in social development. The relative advantages and disadvantages of various weaning ages are discussed. 相似文献
62.
Stimulation of the adenylate cyclase of A B16 melanoma cell line by pro-opiocortin-related peptides--a structure-activity study 总被引:1,自引:0,他引:1
The ability of alpha-melanotrophin (alpha-MSH or ACTH 1-acetyl-13 amide) and other structurally related peptides derived from the common precursor, pro-opiocortin, to stimulate adenylate cyclase activity in a pigmented B16 mouse melanoma was investigated. The peptides ACTH 1-39, ACTH 1-24, alpha-MSH, ACTH 1-13 amide and beta-MSH all stimulated the enzyme to a similar maximal extent and with similar potency (ED50 = 1.3 . 10(-6) M) except that ACTH 1-39 was slightly less potent (ED50 = 5 . 10(-6) M). ACTH 4-10 (ED50 = 4 . 10(-5) M) and gamma-MSH (ED50 = 5 . 10(-6) M) were partial agonists. ACTH 1-10 was no more effective than ACTH 4-10 in stimulating the enzyme whereas ACTH 1-13 amide was a full agonist. The peptides beta-endorphin and its derivatives, Met-enkephalin and melanotrophin potentiating factor (MPF), failed to stimulate the enzyme. We suggest that the B16 melanoma requires not only the sequence ACTH 4-10 but also some part of the sequence ACTH 11-13, or a similar sequence in the terminal portion of beta-MSH, for full activation of the receptor-linked enzyme. 相似文献
63.
Dr. P. N. Dilly 《Cell and tissue research》1977,180(3):367-381
Summary The surface of the Rhabdopleura zooid is ciliated. The cilia of the cephalic shield and tentacles have paddle-like swellings of the shaft. These swellings are usually about 0.6–1 m in diameter and most frequently found in the distal 1–2 m of the ciliary shaft. Others are found in other positions along the length of the cilium and it is suggested that at least some of these swellings represent material transport within the cilium.Paddle shaped cilia are probably more efficient than normal cilia in moving water and food particles. If these cilia are involved in the building of the tubular coenecium then their distribution suggests that the tentacles as well as the cephalic shield are actively involved in tube building.I should like to thank the director and staff of the Marine Biological Laboratory, Plymouth, for collecting the material and the generous loan of facilities during the preparation of the material. Mr. R. Moss provided skillful technical and photographic assistance 相似文献
64.
Effects of amphotericin B on the electrical properties ofNecturus gallbladder: Intracellular microelectrode studies 总被引:2,自引:0,他引:2
Luis Reuss 《The Journal of membrane biology》1978,41(1):65-86
Summary Intracellular microelectrode techniques were employed to study the mechanism by which amphotericin B induces a transient mucosa-negative transepithelial potential (V
ms) in the gallbladder ofNecturus. When the tissue was incubated in standard Na-Ringer's solution, the antibiotic reduced the apical membrane potential by about 40 mV, and the basolateral membrane potential by about 35 mV whereas the transepithelial potential increased by about 5 mV. The electrical resistance of the apical membrane fell by 83%, and that of the basolateral membrane by 40%; the paracellular resistance remained unchanged. Circuit analysis indicated that the equivalent electromotive forces of the apical and basolateral membranes fell by 35 and 11 mV, respectively. Changes in potentials and resistances produced by ionic substitutions in the mucosal bathing medium showed that amphotericin B produces a nonselective increase in apical membrane small monovalent cation conductance (K, Na, Li). In the presence of Na-Ringer's on the mucosal side, this resulted in a reduction of the K permselectivity of the membrane, and thus in a fall of its equivalent emf. During short term exposure to amphotericin B,P
Na/P
Cl across the paracellular pathway did not change significantly, whereasP
K/P
Na doubled. These results indicate that V
ms is due to an increase of gNa across the luminal membranes of the epithelial cells (Cremaschiet al., 1977,J. Membrane Biol.
34:55); the data do not support the alternative hypothesis (Rose & Nahrwold, 1976.J. Membrane Biol.
29:1) that V
ms results from a reduction in shuntP
Na/P
Cl acting in combination with a rheogenic basolateral Na pump. 相似文献
65.
Using a model proposed earlier by Goel et al. and a set of plausible motility rules, a computer simulation of engulfment of two or more intact embryonic tissues is successfully carried out. The same motility rules are used to simulate the rounding up of a tissue, centralization of one tissue within another tissue (a phenomenon not yet observed), and phase inversion, a process which may have relevance to differentiation. The finnal structures bear a good resemblance to those observed experimentally. The software, in conjunction with an appropriate hardware configuration, allows a visual display of the dynamics of cellular movement. These simulations indicate that the range of inter-cellular interactions controlling these tissue rearrangements extends only one or two cell diameters. 相似文献
66.
The effect of the natural ATPase inhibitor and octylguanidine on the ATPase activity of soluble oligomycin-insensitive mitochondrial F1 were compared. Both compounds induced a maximal inhibition of 60–80% in various preparations of F1 studied. The inhibition was of the uncompetitive type with respect to MgATP, and the action of the compounds was partially additive. The data suggest that octylguanidine reproduces the action of the natural ATPase inhibitor. Alkylammonium salts also affect the ATPase activity in a similar form. F1 bound to Sepharose-hexylammonium is largely inactive, whilst free hexylammonium at higher concentrations induces only a partial inhibition of the activity. This suggests that the degree of immobilization of F1 is related to the magnitude of inhibition of ATPase activity induced by alkyl cations. The binding of F1 to Sepharose-hexylammonium is prevented by high concentrations of Na+ or K+. 相似文献
67.
68.
A vibrational study of the CD2 stretching bands of selectively deuterated palmitic and stearic acids
The C-D stretching regions of the infrared and Raman spectra of 14 different palmitic and stearic acids containing isolated CD2 groups are reported. Anomalous behaviour is observed when substitution occurs near the terminal methyl group, which behaviour can not be explained in terms of crystal field effects. 相似文献
69.
Elena C. McCoy G.David McCoy Herbert S. Rosenkranz 《Biochemical and biophysical research communications》1982,108(3):1362-1367
Characterization of a mutant strain (TA98/1,8-DNP6) resistant to the mutagenicity of nitrated polycyclic aromatic hydrocarbons (nitroarenes) revealed that it was also non-responsive to the mutagenic action of nitroso- and N-hydroxylaminoarenes. The mutant strain was fully sensitive to the mutagenic action of the corresponding hydroxamic acid ester. These results suggest that TA98/1,8-DNP6 is deficient in a specific esterifying enzyme and that esterification of the penultimate mutagenic metabolites of nitro- and aminoarenes (, arylhydroxylamines) to form potent electrophiles is controlled by a specific gene. 相似文献
70.
Robert A. Schlegel Bonnie M. Phelps Gary P. Cofer Patrick Williamson 《Experimental cell research》1982,139(2):321-328
Mammalian erythropoiesis includes a step in which the nucleus is extruded through the cell membrane. We have investigated the relationship between concanavalinA (conA) plasma membrane receptors, which are known to leave the incipient reticulocyte during enucleation, and regions of the plasma membrane which bind merocyanine 540, a differentiation-specific marker of hematopoietic cells. The distribution of these two fluorescent probes was examined on living cells from the spleens of neonatal mice and on erythroleukemia cells induced to enucleate in culture. In both cases, the region of the membrane extruded with the nucleus preferentially binds conA and merocyanine 540, whereas the plasma membrane which is left behind retains the capacity to bind another lectin, wheat germ agglutinin (WGA). The implications of these findings are discussed with respect to the mechanism by which markers are eliminated from the erythrocyte cell surface. 相似文献