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121.
S. H. Kim Kyung Woo Cho S. H. Chang Sung Zoo Kim Soo Wan Chae 《Pflügers Archiv : European journal of physiology》1997,434(4):362-372
The mechanism by which glibenclamide regulates mechanically activated atrial natriuretic peptide (ANP) secretion was investigated
using isolated perfused rat atria. A reduction in atrial pressure from an experimentally imposed distending pressure stimulated
the secretion of ANP and caused concomitant translocation of extracellular fluid (ECF) into the atrial lumen. The activation
of ANP secretion and ECF translocation were closely correlated with atrial volume changes and the increase in ANP secretion
was a function of the ECF translocation. Glibenclamide (1, 10, 100 μM), an ATP-sensitive K+ (K+
ATP) channel blocker, had no effect on the basal secretion of ANP, suppressed the stimulation of stretch-activated ANP secretion
in a dose-dependent manner, but not the translocation of the ECF. Glipizide (100 μM) and tolbutamide (100 μM), other K+
ATP channel blockers, had similar effects to those of glibenclamide. Suppression by glibenclamide (100 μM) of the stretch-induced
ANP secretion was not observed in atria that had been pretreated with pinacidil (200 μM), an ATP-sensitive K+ channel opener: pinacidil alone had no effect on ECF translocation and ANP secretion. Furthermore, blocking Ca2+ influx by using the Ca2+ channel blocker diltiazem (10 nM), or a Ca2+-depleted medium prevented the suppression of stretch-induced ANP secretion by glibenclamide. In other experiments, atrial
distension produced a slight membrane depolarization of cardiomyocytes; this was accentuated in the presence of glibenclamide.
Furthermore, in single cardiomyocytes, glibenclamide increased the intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner. From these results, we suggest that glibenclamide suppresses atrial release of ANP by blocking
K+
ATP channels and increasing Ca2+ influx and that the K+
ATP channels are associated with the regulation of the mechanically activated ANP secretion from the atria.
Received: 13 May 1996 / Received after revision: 10 February 1997 / Accepted: 5 March 1997 相似文献
122.
Anatol G. Feldman Serge V. Adamovich Mindy F. Levin 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1995,103(3):440-450
Two versions of the hypothesis that discrete movements are produced by shifts in the system's equilibrium point are considered. The first suggests that shifts are monotonic and end near the peak velocity of movement, and the second presumes that they are nonmonotonic (N-shaped) and proceed until the end of movement. The first version, in contrast to the second, predicts that movement time may be significantly reduced by opposing loads without changes in the control pattern. The purpose of the present study was to test the two hypotheses about the duration and shape of the shift in the equilibrium point based on their respective predictions concerning the effects of perturbations on kinematic and EMG patterns in fast elbow flexor movements. Subjects performed unopposed flexions of about 55–70° (control trials) and, in random test trials, movements were opposed by spring-like loads generated by a torque motor. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. After the end of the movement, the load was removed leading to a secondary movement to the same final position as that in control trials (equifinality). When the load was varied, the static arm positions before unloading and associated joint torques (ranging from 0 to 80–90% of maximum voluntary contraction) had a monotonic relationship. Test movements opposed by a high load (80–90% of maximal voluntary contraction) ended near the peak velocity of control movements. Phasic and tonic electromyographic patterns were load-dependent. In movements opposed by high loads, the first agonist burst was significantly prolonged and displayed a high level of tonic activity for as long as the load was maintained. In the same load conditions, the antagonist burst was suppressed during the dynamic and static phases of movement. The findings of suppression of the antagonist burst does not support the hypothesis of an Nshaped control signal. Equally, the substantial reduction in movement time by the introduction of an opposing load cannot be reconciled in this model. Instead, our data indicate that the shifts in the equilibrium point underlying fast flexor movements are of short duration, ending near the peak velocity of unopposed movement. This suggests that kinematic and electromyographic patterns represent a long-lasting oscillatory response of the system to the short-duration monotonic control pattern, external forces and proprioceptive feedback. 相似文献
123.
The purpose of this study was to investigate whether acute passive stretching (APS) reduced maximal isometric voluntary contraction (MVC) of the plantar flexors (PF) and if so, by what mechanisms. The PF in 15 female volunteers were stretched for 10 min (5×120 s) by a torque motor to within 2° of maximum dorsiflexion (D) range of motion (ROM). MVC with twitch interpolation, maximal Hoffmann reflex (Hmax) and compound action potentials (Mmax) were recorded at 20° D. Stretch reflexes (SR) were mechanically induced at 200° s–1 between 0° and 10° D and SR torque and EMG amplitude were determined. All tests were assessed pre- (pre) and post-APS (post-test1). MVC, SR, and Mmax were again assessed after additional stretch was applied [mean 26 (1)° D; post-test2] to test if the optimal angle had been altered. EMG was recorded from soleus (SOL), medial gastrocnemius (MG) and tibialis anterior (TA) using bipolar surface electrodes. APS resulted in a 27% decrease in mean peak passive torque (P<0.05). MVC and SR torque were 7% (P<0.05) and 13% lower at post-test1 (P<0.05), respectively. SR EMG amplitude of SOL and MG was reduced by 27% (P<0.05) and 22% (P<0.05), respectively. The Hmax/Mmax EMG and Hmax/Mmax torque ratios were unchanged at post-test1. At post-test2, MVC and SR EMG recovered to pre-APS values, while the SR and Mmax torque increased by 19% and 13%, respectively (P<0.05). The decrease in MVC during post-test1 was attributed to changes in the mechanical properties of PF and not to reduced muscle activation. 相似文献
124.
乙肝患者外膜蛋白血清学检测及对于判定HBV DNA复制的意义 总被引:14,自引:2,他引:14
目的探讨HBV感染者血清中PreS1-Ag、PreS2.Ag、大蛋白(LP)的检测意义及其对判定HBV复制的意义。方法应用酶联免疫吸附试验(ELISA)检测201例HBV感染血清的PreS1-Ag、PreS2-Ag、HBV-LP及HBVM,同时应用荧光定量PCR方法检测HBVDNA。结果PreS1-Ag、PreS2-Ag、LP、HBsAg阳性率差异有统计学意义,PreS2-Ag、LP检出阳性率均高于HBeAg;LP的检出阳性率与HBVDNA的检出阳性率相关性有统计学意义,且HBV DNA拷贝数的对数值与HBV-LP表达呈正相关。结论PreS1-Ag、PreS2-Ag、LP较准确的反映乙肝病毒的复制情况,是HBVM有益的必要补充;血清中HBV-LP的含量与HBVDNA的拷贝数具有较好的相关性。 相似文献
125.
In anaesthetized rabbits the effects of high frequency ventilation (HFV) on breathing pattern and on stretch receptor (SR) activity were examined in order to elucidate the mechanism underlying the inhibition of respiration during HFV. An attempt was undertaken to compare the effects of HFV with those of static lung inflations.HFV applied in frequencies between 5 Hz and 25 Hz and with peak airway pressure (Paw) between 5 and 15 cm H2O led — proportionally to Paw — to a gradual prolongation of expiration up to an apnoea. Similar effects occurred during lung inflations, although at higher Paw than during HFV. HFV-induced apnoea was accompanied by a tonic phrenic and diaphragmatic activity which was absent during inflation-induced apnoea.In addition to the activity due to spontaneous breathing, during HFV the SR discharge rate increased with each positive airflow pulse particularly in the expiratory phase, whereas the inspiratory discharge rate was less affected. During static lung inflations there was a parallel increase of both inspiratory and expiratory SR activity, the expiratory discharge rate, however, remaining lower and the inspiratory discharge rate rising more than during HFV.It is concluded that the HFV-induced increase of expiratory SR discharge rate may account for the inhibition of spontaneous breathing during HFV. The persistence of phrenic and diaphragmatic activity during HFV-induced apnoea is thought to be due to activation of irritant receptors. 相似文献
126.
N.?Mrachacz-KerstingEmail author T.?Sinkjaer 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,151(1):72-81
Reflex responses to unexpected stretches are well documented for selected muscles in both animal and human. Moreover, investigations
of their possible functional significance have revealed that stretch reflexes can contribute substantially to the overall
stiffness of a joint. In the lower extremity only the muscles spanning the human ankle joint have been investigated in the
past. This study implemented a unique hydraulic actuator to study the contributions of the knee extensor stretch reflex to
the overall knee joint torque. The quadriceps muscles were stretched at various background torques, produced either voluntarily
or by electrical stimulation, and thus the purely reflex mediated torque could be calculated. The stretch had a velocity of
67°/s and an amplitude of 20°. A reflex response as measured by electromyography (EMG) was observed in all knee extensors
at latencies of 26 – 36 ms. Both phasic and tonic EMG stretch responses increased with increasing background torques. Lines
of best fit produced correlation coefficients of 0.59 – 0.78. This study is the first to examine the reflex contribution of
the knee extensors to the total torque at background torques of 0 – 90% MVC. The contribution of the reflex mediated torque
is initially low and peaked at background torques of 20 – 40% MVC. In terms of the total torque the reflex contributed 16
– 52% across all levels of background torque. It is concluded that during medium background torque levels such as those obtained
during walking, the stretch reflex of the quadriceps muscle group contributes substantially to the total torque around the
knee joint. 相似文献
127.
Goto K Okuyama R Sugiyama H Honda M Kobayashi T Uehara K Akema T Sugiura T Yamada S Ohira Y Yoshioka T 《Pflügers Archiv : European journal of physiology》2003,447(2):247-253
Effects of heat stress, mechanical stretching or a combination of both on the expression of heat shock proteins (HSPs) and total protein level were studied in a culture system. Rat skeletal muscle cells (L6) were cultured on flexible-bottomed culture plates. They were subjected to one of the four following conditions: (1) 97 h incubation at 37 °C, (2) 1 h incubation at 41 °C followed by 96 h incubation at 37 °C, (3) 1 h incubation at 37 °C followed by 96 h cyclic stretching (18% of initial length, 2-s stretch and 4-s release) at 37 °C or (4) 1 h incubation at 41 °C followed by 96 h cyclic stretching at 37 °C. The expression of HSP72 and HSP90 and total protein was determined in the crude homogenates, supernatant and pellets. Cellular protein concentrations in the homogenates and pellets were increased by heat stress and/or mechanical stress (stretch). A cumulative effect of the combination of heating and stretch on the protein concentration in the homogenates and in the pellets was noted. The expressions of HSP72 and HSP90 in the pellets were also increased by heat stress and/or stretch. However, HSP90 in the supernatant did not change following heat stress and/or stretch. The regulation of HSP72 and HSP90 expression in skeletal muscle cells may be closely related to total protein, the abundance of which is also stimulated by mechanical and heat stresses. These observations suggest strongly that heating and passive stretch of muscle may be useful as a means of increasing muscle mass, not only in athletes but also in patients during rehabilitation. 相似文献
128.
Clonus after human spinal cord injury cannot be attributed solely to recurrent muscle-tendon stretch
Beres-Jones JA Johnson TD Harkema SJ 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,149(2):222-236
Clonus, presented behaviorally as rhythmic distal joint oscillation, is a common pathology that occurs secondary to spinal
cord injury (SCI) and other neurological disabilities. There are two predominant theories as to the underlying mechanism of
clonus. The prevailing one is that clonus results from recurrent activation of stretch reflexes. An alternative hypothesis
is that clonus results from the action of a central oscillator. We present evidence that the mechanism underlying clonus in
individuals with SCI is not solely related to muscle stretch. We studied electromyography (EMG) of the soleus (SOL), medial
gastrocnemius (MG), tibialis anterior (TA), medial and lateral hamstrings, vastus medialis, vastus lateralis, and rectus femoris
from subjects with clinically complete and clinically incomplete SCI during stretch-induced ankle clonus, stepping, and non-weight-bearing
standing. Clonic EMG of the SOL, MG, and TA occurred synchronously and were not consistently related to muscle-tendon stretch
in any of the conditions studied. Further, EMG activity during stretch-induced ankle clonus, stepping, and non-weight-bearing
standing had similar burst frequency, burst duration, silent period duration, and coactivation among muscles, indicating that
clonic EMG patterns occurred over a wide range of kinematic and kinetic conditions, and thus proprioceptive inputs. These
results suggest that the repetitive clonic bursts could not be attributable solely to immediate afferent feedback such as
recurrent muscle stretch. However, these results support the theory that the interaction of central mechanisms and peripheral
events may be responsible for clonus.
Electronic Publication 相似文献
129.
A. Gollhofer V. Strojnik W. Rapp L. Schweizer 《European journal of applied physiology》1992,64(4):283-291
Summary The force-length relationship of the human muscle-tendon complex (MTC) of the triceps surae and the achilles tendon was investigated in various stretch load conditions. Six male subjects performed various vertical jumps with maximal effort: squat jumps (SJ), counter movement jumps (CMJ) and drop jumps (DJ) from a height of 24 cm, 40 cm and 56 cm. The force-length relationship was calculated from the signals of the components of the ground reaction forces and the kinematic data obtained from the high-speed film records. Surface electromyograms (EMG) of the soleus, gastrocnemius and tibialis anterior muscles were also recorded. The force-length diagrams showed individually high sensitivity to the imposed stretch load. In conditions with relatively low stretch load requirements there was a counter-clockwise direction observable, indicating that the energy absorbed during the eccentric, or lengthening phase was lower than the energy delivered during the concentric, or shortening phase. In high load conditions this relationship was reversed indicating a negative energy balance. The EMG-length diagrams of SJ and CMJ consisted of an initial isometric loading of the muscle, followed by a shortening phase with only slightly reduced EMG amplitudes. In DJ, however, the diagrams showed an initial lengthening of the MTC with fairly constant activation amplitudes. After 40 ms an isometric loading of the muscle, lasting for approximately 80 ms, was followed by a shortening phase. It was concluded that segmental stretch reflex activation represented the predominant activation process during the isometric loading phase, to meet the adequate stiffness properties of the MTC. 相似文献
130.
Puchert E Andruchov O Wagner A Grassberger H Lahnsteiner F Sobieszek A Galler S 《Pflügers Archiv : European journal of physiology》2003,447(2):135-141
The effects of changes in Mg2+ concentration on the kinetics of stretch activation were investigated on skinned rat heart preparations under maximal Ca2+ activation. Muscle strips of hyper- and hypothyroid rat hearts were investigated at 0.5 and 1 mM free Mg2+; the total ATP concentration was 8 mM which resulted in saturating MgATP2– concentrations above 5 mM. Preparations containing exclusively the cardiac -myosin heavy chain (hyper- and hypothyroid atria, hyperthyroid ventricles) showed an acceleration of the kinetics of stretch activation by a factor of about 1.5 (P<0.01, paired t-test) when free Mg2+ was decreased from 1 to 0.5 mM. Conversely, preparations containing exclusively the -myosin heavy chain isoform showed only a small acceleration by a factor of 1.05 (P<0.05, paired t-test) under the same conditions. The fact that the Mg2+ sensitivity was dependent on the myosin heavy chain isoform excludes the possibility that Mg2+ exhibits only unspecific effects on contractile proteins. Several hypotheses for explaining the observed Mg2+ effects are discussed. The conditions used in our experiments might be close to the physiological situation and, thus, changes of Mg2+ concentration must be considered as possible factors modulating the contractile kinetics especially of atrial muscle tissue. 相似文献