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101.
A volumetric method has been developed which permits continuous registration of volume flows across epithelial tissues. The method was applied to volume flow measurements across rabbit gall bladder epithelium. The rate of fluid reabsorption measured in this way was twice as high as previously observed in sac preparations of the gall bladder. This is probably due to better aeration and stirring of the mucosal solution. It was demonstrated that electrical gradients across the gall bladder induced volume flows towards the negative electrode. In non-transporting bladders volume flows were linearly related with current between 300 and 900 μA in both directions. However, volume flow rates were three times higher from mucosa to serosa than in the opposite direction. From the magnitude of polarization potentials, observed after switching off the current, the conclusion was reached that all of the current-induced volume flow is an osmotic flow due to salt polarization in the unstirred layers of the tissue. By implication, so-called streaming potentials observed during osmotic flows reflect solely polarization effects. In actively transporting gall bladders a 200 μA current increased or decreased the flow rate twice as much as expected from polarization effects alone. Therefore passage of current interfered directly with the active transport mechanism of gall bladder epithelium. 相似文献
102.
Heterogeneity in the conformation of different protein fractions from the human erythrocyte membrane
We have isolated 5 families of proteins from human red blood cell membranes and characterized their secondary structure by ultraviolet circular dichroism measurements. The protein families were prepared by selective solubilization from ghosts under nondenaturing conditions. We find that the intact ghost has a mean α-helix fraction of 0.37, whereas a low-ionic-strength extract (bands 1, 2, 5, “spectrin”) has a substantially higher helix fraction, 0.55. Further extraction of the ghosts with para-chloromercuribenzoate yields bands 2.1, 4.1, 4.2, and 6; their helix content is only 0.17. Finally, the major intrinsic protein, band 3, was solubilized by a nonionic detergent. Its helix fraction is 0.38. 相似文献
103.
Electrical and structural properties of crayfish claw motoneurons in an isolated claw-ganglion preparation 总被引:2,自引:0,他引:2
Theodore J. Wiens 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1976,112(2):213-233
1. | An isolated claw-ganglion preparation of the crayfish is described in which reflex activity is maintained for eight hours or more. |
2. | Intracellular recording and cobalt injection have made it possible to locate and characterize the claw motoneurons. Soma recordings show attenuated axon spikes of 5–10 mV amplitude and subthreshold potentials of the same magnitude. |
3. | The fast closer excitor (FCE) receives subthreshold excitation in parallel with the slow closer excitor (SCE) and the opener inhibitor (OI) even though it seldom fires. |
4. | IPSP's are recorded in the opener excitor (OE) concurrent with OI spikes. |
5. | Cobalt injection reveals a parallel dendritic structure among the three synergists FCE, SCE and OI, and a distinctly different dendritic distribution for OE. The soma siza ranking: OI<>FCE = SCE is apparent. |
6. | The results are discussed and compared with other arthropod systems with regard to the relation between soma size and electrical functions, distribution of somata and dendrites, and effects of cobalt on electrical functioning. A conflict with previous work on this system is discussed. |
104.
The Genetics of Dopa Decarboxylase in DROSOPHILA MELANOGASTER I. Isolation and Characterization of Deficiencies That Delete the Dopa-Decarboxylase-Dosage-Sensitive Region and the α-Methyl-Dopa-Hypersensitive Locus 总被引:5,自引:5,他引:0
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A detailed cytogenetic investigation of 16 overlapping deficiencies in the 36C-40A region on the left arm of the second chromosome (2L) in Drosophila melanogaster is reported. These deficiencies permit a localization of both the dopa-decarboxylase-dosage-sensitive region and the α-methyl-dopa-hypersensitive locus, l(2)amd, to the same region, 37B10-37C7. 相似文献
105.
Anya N. Metcalfe Jeffrey D. Muehlbauer Theodore A. Kennedy Charles B. Yackulic Kimberly L. Dibble Jane C. Marks 《Freshwater Biology》2021,66(1):89-101
- Most of the world's large rivers are dammed for the purposes of water storage, flood control, and power production. Damming rivers fundamentally alters water temperature and flows in tailwater ecosystems, which in turn affects the presence and abundance of downstream biota.
- We collaborated with more than 200 citizen scientists to collect 2,194 light trap samples across 2 years and more than 2,000 river km. Samples contained 16,222 net‐spinning caddisfly (Hydropsyche) individuals across six species. We used these data to model the distribution of Hydropsyche throughout the Colorado River Basin in the western U.S.A. to identify the roles of water temperature, flows, and species‐specific morphology in determining aquatic species distributions throughout a large arid watershed that has been heavily altered by damming.
- We predicted that water temperatures would determine Hydropsyche presence and abundance to a greater extent than diel variation in river stage associated with hydropower production. Among many species, adult female Hydropsychids are morphologically adapted to swim to deep‐water oviposition sites. We predicted that the presence of this ability would negate the otherwise deleterious effects of high stage change on caddisfly egg mortality.
- We found that distributions of the two most widespread species, Hydropsyche occidentalis and Hydropsyche oslari (92% of total Hydropsyche captured), were both predicted by water temperatures. However, we also found that the abundance of H. oslari decreased by as much as 10‐fold as diel stage change increased, despite the presence of female morphological adaptations for deep‐water oviposition. We found sexual dimorphism and evidence for deep‐water swimming adaptations in 5/6 species.
- Our results show that net‐spinning caddisflies have species‐specific responses to environmental variation and suggest that environmental flows designed to reduce diel stage change and destabilise water temperatures may improve habitat quality for these ubiquitous and important aquatic insects.
106.
Theodore Dalrymple 《BMJ (Clinical research ed.)》2007,335(7629):1099
107.
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109.
The persistence of short‐term cold acclimation in Drosophila melanogaster (Diptera: Drosophilidae)
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Elizabeth R. Everman Nicholus Ledbetter Theodore J. Morgan 《Physiological Entomology》2017,42(4):291-298
Daily and seasonal fluctuations in temperature present significant challenges for the survival of many ectothermic species that can be tempered via thermal acclimation. In the present study, we use multiple naturally derived genotypes of Drosophila melanogaster to determine the persistence of beneficial short‐term thermal acclimation on subsequent survival after cold shock. We found that the benefit of short‐term acclimation persisted for 2 h in most genotypes after a rapid cold hardening treatment. Genotype did not directly influence the persistence of short‐term acclimation benefits, indicating that environmental variation may be more important for the persistence of acclimation benefits rather than genetic capacity for acclimation. The present study extends the current understanding of the limits and importance of short‐term acclimation events, providing greater detail on the timing of the loss of short‐term acclimation benefits in a genetically variable natural population. 相似文献
110.