Résumé
Objective To investigate the effects of sevoflurane on ca2+ transsarcolemmal influx and ca2+ release function of endoplasmic reticulum in isolated outer hair cells (OHCs) of guinea pigs and the possible mechanism by which sevofhlrane acts on cochleas.Methods The experiment was performed in 2 parts.In experiment I:twelve adult guinea pigs(8 male,4 female)weighing 180-230 g were used.OHCs were mechanically sparated after enzymatic incubation.Thirty OHCs with favorable activity were divided into 3 groups (n=10 each):group I control(C);group Ⅱ low concentration sevoflurane (1.7%,group S1) and group Ⅲ high concentration sevoflurane(3.4%,group S2).The OHCs were stained with 6 umol/L Fluo-3AM in estefified form for 40 min.Group S1 and S2 were pretreated with 1.7% and 3.4% sevoflugsne respectively for 20 min.KCI 40 mmol/L was then added.The intracellular ionized Ca2+ concentration ([C2+]I) was determined byintracelhlar Ca2+ fluorescent intensity using laser scanning confocal microscope.The protocol of the experimentⅡ was the same as the experimentI.The only difference was that caffeine 20 mmol/L was added instead of KCI 40 mmol/L.Results In experiment I:there was no significant difference in baseline[ca2+]I and[ca2+]I after being exposed to sevoflurane among the 3 groups.[Ca2+]I was significanfly increased after addition of KCI as compared with the baseline[Ca2+]I and was significantly lower in group Sl and S2 than in group C and was the lowest in group S2.In experimentⅡ:the[ca2+]I was significantly increased after addition of caffeine but there was no significant difference in[Ca2+]I among the 3 groups.Conclusion Sevoflurane can inhibit voltage-dependent Ca2+ channel opening in a concentration-dependent manner but can not affect ryanodine-sensitive Ca2+ release function of endoplasmic reticuhm in isolated outer hair cells of guinea pigs.
Résumé
Objective To observe the space-time patterns of damaged outer hair cells(OHCs) in rat cochlea at the early stage after exposure to impulse noise. Methods Wistar rats were exposed to 100 emissions of impulse noise (3 seconds interval between each emission) at 154 dB SPL. Four times (10 min, 30 min, 3h and 6h) after the noise exposure, the animals were sacrificed and the organs of Corti were processed for detection of OHC death modes. The apoptotic and necrotic OHCs were distinguished by propidium iodide (PI), a fluorescent probe specifically labeling the nuclear DNA. The specimens were examined under a fluorescence microscope for assessment of OHC damage. Results Nuclear chromatin began to shrink as the chromatin condensed around the nuclear periphery. The peripheral chromatin ring condensed into discrete mass. Chromatin masses appeared to bleb off from the nuclear surface, forming apoptotic bodies at 10 min after the noise exposure. There were a few swollen nuclei appeared 30 min after the noise exposure. Loss of OHC nuclei could be seen 3 h after the noise exposure. The cochlear lesion expanded to contain a large number of missing OHCs and seriously shrunken nuclei at 6 h after the noise exposure. Conclusions The results of the study indicate that death of OHCs takes place extremely rapid after the impulse noise exposure. The apoptosis of OHCs precedes necrosis. OHC apoptosis is a quick process. Most of dead outer hair cells were eliminated 6 h after the noise exposure.
Résumé
Objective To quantitatively analyze the occurrence of apoptotic and necrotic outer hair cells (OHCs) and to evaluate the changes of these parameters with time after noise exposure. Methods Chinchillas were exposed to a narrow band noise at either 104 or 108 dB SPL for 1 hour. The animals were executed and dissected at either 1, 4 and 30 days after the noise exposure and the cochleas were collected for detection of OHC death mode. The apoptotic and necrotic OHCs were distinguished by examining the OHC nuclear morphology and confirmed by staining for caspase 3 activity or TUNEL assay. ABR thresholds for click stimuli were used to monitor changes in auditory function. Results The number of apoptotic cells were significantly greater than those of necrotic cells shortly after the noise exposure at day 1 for the 104 dB group, day1 and day4 for 108 dB group ( P =0 01, P =0 03, P =0 01) and the difference between the number of apoptotic cells and necrotic cells became statistically insignificant at day 4 and day 30 for the 104 dB group and day 30 for 108 dB group ( P =0 67, P =0 29, P =0 52). By day 30, apoptotic and necrotic pathologies continued, although in small quantity in both 104 dB group and 108 dB group. Conclusions The results of the study indicated that the early expansion of cochlear lesion is contributed primarily by apoptosis, whereas the later stage of lesion expansion is likely contributed equally by apoptosis and necrosis. The death of OHCs not only takes place during a noise exposure, but also continues for at least 30 days after noise exposure