Effects Of Exercise On Mitochondrial Permeability Transition Pore And Apoptosis In Rat Skeletal Muscle

Apoptosis, which is the basically physiological mechanism, is important to renew the normal cells and eliminate the abnormal cells for the multicellular organism. Mitochondria plays a centering control part in apoptosis. The opening state of mitochondrial permeability transition pore determines the mitochondrial membrane permeability, which is crucial to regulate apoptosis: cytochrome c is released from mitochondria to cytoplasm, activates caspases via combining Apaf-1 and ATP, initiating caspases cascade, hydrolyze substrate protein, form apoptosis body etc, cause apoptosis; Bcl-2 and Bax are two important regulating genes in the process of apoptosis, the increase of Bcl-2 expression can inhibit the cell apoptosis and the excessive expression of Bax can accelerate the cell apoptosis; The mitochondria absorbs calcium during the cell apoptosis, which can not only result in mitochondrial permeability transition pore opening but also cause calcium induced calcium release from mitochondria, the high concentration of calcium in cytoplasm can activate kinds of protein kinase so that apoptosis occurred. The study adopted two different exercise modes. The opening state of mitochondrial permeability transition pore in skeletal muscle was measured with ultraviolet spectrophotometer and the release of cytochrome c from the mitochondria was measured with western blot. Meanwhile, the expression of related genes regulating permeability transition pore opening were measured with RT-PCR and the calcium transfer from mitochondria was detected with double beams of light ultraviolet spectrophotometer in order to discuss the mechanism of the mitochondrial permeability change in skeletal muscle, to study the effect of the mitochondrial opening on the cell apoptosis and the mechanism of exercises affect mitochondrial permeability transition pore opening and apoptosis.Methods: 24 male Sprague-Dawley rats, whose weight is 221.6±17.4 gram, took adaptive feeding in the lab for three days and was followed by adaptive swimming for five days. Then they were randomly divided into three groups: control group (n=8), six weeks' swimming training group (n=8) and one-off exhaustive swimming group (n=8). The control group took normal feeding without training and was killed at rest 6 weeks later; The six weeks' swimming training group undertook swimming training for six weeks, then was killed 24 hours later after the last training; The one-off exhaustive swimming group took normal feeding for 6 weeks, then was killed immediately after one-off exhaustive swimming. The thigh quadriceps were isolated from all three groups to measure the opening of mitochondrial permeability transition pore, the transfer of calcium from mitochondria, the release of cytochrome c from mitochondria and the expression of Bcl-2 and Bax mRNA which regulate the opening of PTP.Results: (1) The mitochondrial absorbency in skeletal muscle in six weeks' swimming training rats had the trend to increase, but without significancy compared with control group, suggested that MPTP opening didn't change significantly; However, the mitochondrial absorbency in one-off exhaustive swimming rats decreased significantly and it suggests that MPTP opened significantly.(2) According to the result of western blotting, we can see that the release of cytochrome c from mitochondria in six weeks' swimming training mice decreased remarkably, but the release of cytochrome c from mitochondria in one-off exhaustive swimming mice increased significantly compared with control group.(3) Compared with control group, there was no significant change of calcium transfer in six weeks' swimming training rats; but the calcium transfer significantly increased in the one-off exhaustive swimming rats.(4) Six weeks' swimming training resulted in the significant increase of Bcl-2 mRNA expression and the significant decrease of Bax mRNA expression compared with control group; but contrary to this, the expression of Bcl-2 mRNA decreased remarkably and at the same time Bax mRNA expression increased significantly compared with control group in the one-off exhaustive swimming mice.Conclusion: (1) Six weeks' swimming training did not result in MPTP opening or calcium transfer significantly in rats skeletal muscle, but cytochrome c release from mitochondria decreased evidently, the expression of Bcl-2 mRNA enhanced significantly and Bax mRNA expression declined significantly, suggests that six weeks' swimming training might decrease caspases cascade through reducing the release of cytochrome c from the mitochondria, then activated caspases decreased and apoptosis decreased. The ratio of Bcl-2 and Bax increased and the ability to resist apoptosis is enhanced.(2) One-off exhaustive swimming resulted in mitochondrial PTP opening and calcium transfer increased significantly, the high concentration of calcium in the cytoplasm accelerated cell apoptosis; The increased release of cytochrome c initiated caspases cascade, activated more caspases and accelerated cell apoptosis; The expression of Bcl-2 mRNA decreased and Bax mRNA expression increased significantly. The decreased ratio of Bcl-2 and Bax made the skeletal muscle apoptosis increased.