Receptor-operated regulation of ATP-sensitive K+ channels via membrane phospholipid metabolism

ATP-sensitive K(+) channels (K(ATP)channels) regulate insulin secretion by coupling intracellular metabolic changes to excitability of the plasma membrane in pancreatic beta-cells. The channels are closed when extracellular glucose levels are elevated due to enhanced feature. By contrast, cardiac-type K(ATP) channels, which open in response to metabolic stress during cardiac ischemia, shorten action potential durations. This may contribute to the cardioprotection by decreasing Ca(2+) influx through sarcolemma. By sensing intracellular ATP levels or ATP/ADP ratios, changes in activity of K(ATP) channels convert metabolic information into membrane excitability. In addition to channel regulation by nucleotide concentrations, the channel activity is also dependent on the concentrations of membrane phospholipids, including phosphatidyl inositol-4,5-bisphosphate (PIP(2)). The levels of PIP(2) in the membrane may determine the basal activity of the channels. This suggests that channel activity would be modulated by the pathway of receptor-coupled GTP-binding protein (G-protein) and phosphatidyl inositol phospholipase C (PI-PLC) stimulation, which brings about depletion of the membrane PIP(2) pool. Thus, K(ATP) channels not only provide interface of metabolic changes with electrical excitation, but also rapidly transmit extracellular signals through receptor-coupled G-protein and PI-PLC pathway via PIP(2) metabolism.     

Toxic effects of chlorpromazine on red and white muscles in rats: An ultrastructural study

Transmission electron microscopy was used to study the effects of chlorpromazine on skeletal muscle in rats. Sixteen male Wistar strain rats were divided into two groups of eight and given either normal saline or chlorpromazine ip at a dose of 50 mg/kg body wt on 7 consecutive days. At the end of the treatment period three of eight rats given chlorpromazine could not walk; there were signs of impaired muscle function in the remaining five. Seven days after the last ip injection, the rats were anesthetized with sodium pentobarbital. The soleus (SOL), a red muscle, and the extensor digitorum longus (EDL), a white muscle, were removed and fixed by immersion in glutaraldehyde for subsequent processing and examination by transmission electron microscopy. Abnormal and degenerative mitochondria were frequently observed in the EDL, but the myofibrils were mostly intact. In contrast, in the SOL, formations of contraction bands and lysis of myofibrils were frequently observed. These results suggested that the effects of chlorpromazine may be different between the red muscle and the white muscle.     

Development of a quantitative evaluation system for motor control using wrist movements--an analysis of movement disorders in patients with cerebellar diseases

In this study, we developed a new system for quantitative evaluation of the wrist movement. We designed this system to analyze the causal relationship between movement disorders and abnormal muscle activities. In addition, this system was also designed to be non-invasive and used handily at the bedside. We tested this system for analysis of movement disorders in the cerebellar patients. As an experimental task, we asked subjects to perform step-tracking wrist movements with a manipulandum, and simultaneously recorded wrist joint movements and muscle activities of four wrist prime movers with surface electrodes. The participants included eight patients with cerebellar diseases and eight normal controls. First, we made quantitative analysis of movement kinematics in the cerebellar patients in terms of accuracy and directional deviation of wrist movements. Then we examined how well the wrist movement could be explained with the activities of the four prime movers. Specifically, we compared the wrist joint torque calculated from the movement of the wrist (kinematic torque) and the wrist joint torque estimated from the muscle activities (muscle torque). Then we evaluated match between the two. Our surprising observation was that there were very high correlations between the kinematic torque and the muscle torque for both normal controls and cerebellar patients. Correlation coefficients R for normal controls were 0.85 +/- 0.06 for X-axis component and 0.78 +/- 0.09 for Y-axis component. On the other hand, correlation coefficients R for cerebellar patients were 0.78 +/- 0.11 for X-axis component and 0.78 +/- 0.1 for Y-axis component. These results strongly suggested that there were enough information in the activities of the four muscles to explain the position, speed and acceleration of the wrist joint. In other words, with our system, it is possible to identify causal abnormality of muscle activities for movement disorders. Therefore, it is possible with our system to analyze movement disorders at a motor command level.     

Risk factors associated with inferior alveolar nerve injury after extraction of the mandibular third molar—a comparative study of preoperative images by panoramic radiography and computed tomography

In this study we investigated the relationships among the risk factors for inferior alveolar nerve injury (IANI), and the difference between preoperative imaging findings on panoramic radiographs and computed tomography (CT), by univariate and multivariate analyses. We determined the following to be significant variables by multivariate analysis: panoramic radiographic signs, such as the loss of the white line of the inferior alveolar canal or the diversion of the canal; excessive haemorrhage during extraction; and a close relationship of the roots to the IAN (type 1 cases) on CT examination. CT findings of type 1 were associated with a significantly higher risk (odds ratio 43.77) of IANI. In addition, many panoramic findings were not consistent with CT findings (275 of 440 teeth; 62.5%). These results suggest that CT findings may be able to predict the development of IANI more accurately than panoramic findings. Panoramic radiography alone did not provide sufficiently reliable images required for predicting IANI. Therefore, when the panoramic image is suggestive of a close relationship between the impacted tooth and the IAN, CT should be recommended as a means of conducting further investigations.     

Iron fortification of rice seeds through activation of the nicotianamine synthase gene

The most widespread dietary problem in the world is mineral deficiency. We used the nicotianamine synthase (NAS) gene to increase mineral contents in rice grains. Nicotianamine (NA) is a chelator of metals and a key component of metal homeostasis. We isolated activation-tagged mutant lines in which expression of a rice NAS gene, OsNAS3, was increased by introducing 35S enhancer elements. Shoots and roots of the OsNAS3 activation-tagged plants (OsNAS3-D1) accumulated more Fe and Zn. Seeds from our OsNAS3-D1 plants grown on a paddy field contained elevated amounts of Fe (2.9-fold), Zn (2.2-fold), and Cu (1.7-fold). The NA level was increased 9.6-fold in OsNAS3-D1 seeds. Analysis by size exclusion chromatography coupled with inductively coupled plasma mass spectroscopy showed that WT and OsNAS3-D1 seeds contained equal amounts of Fe bound to IP6, whereas OsNAS3-D1 had 7-fold more Fe bound to a low molecular mass, which was likely NA. Furthermore, this activation led to increased tolerance to Fe and Zn deficiencies and to excess metal (Zn, Cu, and Ni) toxicities. In contrast, disruption of OsNAS3 caused an opposite phenotype. To test the bioavailability of Fe, we fed anemic mice with either engineered or WT seeds for 4 weeks and measured their concentrations of hemoglobin and hematocrit. Mice fed with engineered seeds recovered to normal levels of hemoglobin and hematocrit within 2 weeks, whereas those that ate WT seeds remained anemic. Our results suggest that an increase in bioavailable mineral content in rice grains can be achieved by enhancing NAS expression.