Background: Loss of occlusal function has been reported to induce atrophic changes in the periodontal ligament. It is likely that mechanical stress triggers the biological response of periodontal ligament. However, there have been few reports studying the correlation between mechanical stress of varying magnitude and periodontal ligament cell activities such as extracellular matrix (ECM) synthesis. Objective: The objective of this study is to clarify the influence of the mechanical stress on changes in mRNA expression levels of type I collagen and decorin genes, as well as alkaline phosphatase (ALP) activity in response to mechanical stress of varying magnitude. Methods: Bovine periodontal ligament cells were cultured on flexible‐bottomed culture plates and placed on the BioFlex Loading Stations™. Cells were elongated at 6 cycles/min (5 s on and 5 s off) at each of six levels of stretch (0.2, 1.0, 2.0, 3.0, 10, 18% increase in the surface area of the bottom) for 48 h. We measured mRNA expression levels of type I collagen and decorin genes using quantitative reverse transcription–polymerase chain reaction (RT–PCR), and ALP activity in periodontal ligament cell culture under cyclic mechanical stretching. Results: Mechanical tensional stress of low magnitude induced the increase of both type I collagen and decorin mRNA expression without changing ALP activity in periodontal ligament cells. Mechanical tensional stress of high magnitude induced the increase of type I collagen and decorin mRNA expression while decreasing ALP activity. Conclusion: These results suggest that different magnitude of tensional force induces different responses from periodontal ligament cells, and that mechanical stress plays an important role in remodeling and functional regulation of periodontal ligament.
By the methods of intracellular microelectrode technique and the bridge circuit for recording the mechanical activity, the effect of external calcium concentration of the cultured chick embryonic heart has been investigated. Trypsin-dispersed cells from the ventricle of 5 days old chick embryos were cultured. The cell clusters became attached to the bottom of cultured-dish. Then, results from trypsin-dispersed cells were compared with those of noncultured intact embryonic hearts. Spontaneous cells were compared with those of non-cultured intact embryonic hearts. Spontaneous cells were discarded and only quiescent cells were driven by electrical field stimulation.1. The reduction of calcium in the external medium strikingly prolonged the duration of action potential in cultured cells, while the amplitude of mechanical activity was prominently decreased.2. In the intact embryonic hearts, the configuration of action potential is not significantly affected by the calcium deficient solution. On the other hand, the effect of calcium deficiency on mechanical activity is more dramatic than that in cultured cells. These results suggest that the inward movement of calcium ion through the membrane plays a significant role in the initiation of contraction.3. The reduced mechanical activity of cultured and intact cells due to calci um deficiency returns to its normal level by the application of g-strophanthin, but the recovery rate was larger in cultured cells.
The effects of 10-5 and 10-4gm/ml sodium 1-thyroxine on the bullfrog's slow muscle fibers innervated by the small motor nerve and on the neuromuscular transmission were investigated by means of the intracellular microelectrodes technique.1. The slow muscle fibers were affected by more than 10-4 thyroxine-Ringer solution. The resting potential was slightly hyperpolarized but insignificantly. The effective membrane resistance, however, considerably increased to three folds of that in the control solution. The neuromuscular transmission was facilitated, i. e. amplitudes of the s. j. p.'s were augmented by 180%. The s. j. c. under the voltage clamp condition was also augmented by 240%, while their durations somewhat decreased.2. Ach-potentials produced by the ionophoretic microapplications of acetyl choline are remarkably increased by 10-4 thyroxine.3. From these evidences, it was concluded that thyroxine accelerated the neuromuscular transmission by both increasing the resting muscle membrane resistance and enhancing the sensitivity of the receptor membrane for the released transmitter substance from the nerve endings. It was also discussed that other factors such as the anticholinesterase-like action of thyroxine and an increase in the amount of the transmitter substance from the nerve endings were not conceivable.4. The relationships between the thyroid hormones and the neuromuscular disorders in the cases of either the thyrotoxic or the familial form of periodic paralysis were discussed.
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