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排序方式: 共有113条查询结果,搜索用时 15 毫秒
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Although exposure of LLC-PK1 epithelial cell sheets to phorbol esters (TPA)
causes a near immediate and total decrease of transepithelial electrical
resistance (TER), continuation of exposure for 3 to 4 days results in a
tachyphylactic response as TER begins to return to control levels. Recovery
of TER is maximal by 5 to 6 days, but reaches only 70 to 80% of control
level. A reciprocal change in the transepithelial flux of D-mannitol
indicates that the TER decrease is indicative of an increase in tight
junction permeability. Exposure of cell sheets to TPA for several days also
results in the appearance of multilayered polyp- like foci (PLFs) across
the otherwise one cell layer thick cell sheets. The pattern of penetration
of the electron dense dye, ruthenium red, from the apical surface, across
the tight junction and into the lateral intercellular space indicates that
the tight junctions of the cell sheet become uniformly leaky after acute
exposure to TPA. However, when exposure is continued for several days, only
the junctions of cells in the PLFs manifest leakiness. The decrease in TER
following acute TPA exposure correlates with the translocation of protein
kinase C-alpha (PKC alpha) into a membrane-associated compartment. With
exposure of several days, only a trace of PKC alpha is visible by Western
immunoblot, and this is in the membrane-associated compartment.
Immunofluorescent microscopy indicates that the trace of PKC alpha seen in
the Western immunoblots is ascribable distinctly to cells of the PLFs.
Monolayer areas between PLFs show no discernible immunofluorescent signal.
The data therefore indicate that tight junction barrier function may be
restored in certain areas by the down regulation of PKC alpha from the
membrane-associated compartment. Failure to down regulate may result in the
paracellular leakiness and abnormal cell architecture of the PLFs. Possible
implications of this model for in vivo epithelial tumor promotion are
discussed.
相似文献
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This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise. Simultaneously presented acoustic noise produced a decrease in ECAP amplitude. The effect of the acoustic masker on the electric probe was greatest at the onset of the acoustic stimulus and it was followed by a partial recovery of the ECAP amplitude. Following cessation of the acoustic noise, ECAP amplitude recovered over a period of approximately 100-200 ms. The effects of the acoustic noise were more prominent at lower electric pulse rates (interpulse intervals of 3 ms and higher). At higher pulse rates, the ECAP adaptation to the electric pulse train alone was larger and the acoustic noise, when presented, produced little additional effect. The observed effects of noise on ECAP were the greatest at high electric stimulus levels and, for a particular electric stimulus level, at high acoustic noise levels. 相似文献
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Hu N Abbas PJ Miller CA Robinson BK Nourski KV Jeng FC Abkes BA Nichols JM 《Hearing research》2003,185(1-2):77-89
The influence of functional hair cells on electrical stimulation of the auditory nerve is an important issue as individuals with significant residual hearing are now cochlear implant candidates. Previous work has shown that chemical deafening during the course of acute experiments changes the auditory nerve's responses to electrical stimulation [Third Quarterly Progress Report, NIH contract N01-DC-9-2106 (2000), Final Report, NIH Contract N01-DC-9-2106 (2002)]. This study extended that work by investigating the changes and subsequent recovery following furosemide injections which reversibly impair hair-cell function [Hear. Res. (1980) 79-89; Hear. Res. 14 (1984) 305-314, J. Physiol. 347 (1984) 685-696; Hear. Res. 71 (1993) 202-207]. Acoustic sensitivity of guinea pig subjects was repeatedly monitored with the click-evoked compound action potential. Responses to single biphasic electric pulses and biphasic electric pulse trains delivered by a monopolar intracochlear electrode were also repeatedly assessed using the electrically evoked compound action potential (ECAP). Our measures demonstrated a clear relationship between the state of hair-cell function and ECAP responses, as changes in the latter coincided with the loss or recovery of acoustic sensitivity. ECAP growth functions demonstrated increased slope and increased maximum (saturation) amplitude. Both trends were reversible and followed approximately the time course of post-furosemide hearing recovery. Additional changes were observed using electric pulse-train stimulation: (1) the magnitude of ECAP amplitude alternation (observed in response to successive stimulus pulses) increased, (2) the degree of ECAP adaptation (measured 80-100 ms after pulse-train onset) increased, and (3) the degree of refractoriness (measured by the ratio of ECAP amplitudes to the second and first pulses) tended to increase. All these trends are consistent with the hypothesis that functional hair cells desynchronize the population of auditory nerve fibers, thereby changing the electrically evoked responses. Viable hair cells may therefore provide positive effects on auditory response to electric stimuli delivered to implant patients with residual hearing, as they may enhance the random activity of the stimulated nerve. 相似文献
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Vivek Pandey Ajay Singh Thakur Kiran KV Acharya P Sripathi Rao 《Indian Journal of Orthopaedics》2009,43(1):97-98
Described as asymptomatic and an incidental finding on a plain x-ray film, the “pelvic digit” is a rare congenital anomaly. A 35-year-old man is of a rare symptomatic pelvic digit that warranted surgical excision. Its importance lies in its differentiation from acquired abnormalities due to trauma such as myositis ossificans and avulsion injuries of pelvis. If this entity is kept in mind, unnecessary investigations or interventions can be avoided. 相似文献
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