Functional Alteration Of Skeletal Muscle Sarcoplasmic Reticulum Ca～(2+) Transport In Rat After Progressively Time-increasing Swimming Training And Exhaustion--Possible Mechanism And Relationship With Blood Biochemical Parameters

The contraction and relaxation of skeletal muscles depends on the relative movements of thin and thick myofilaments. Normal muscular activity is closely related to the functional status of contractile apparatus, sarcoplasmic reticulum (SR), and various regulatory capacities in myocytes during excitation-contraction coupling (EC). Of these, the SR Ca2+ transport is one of most key events during skeletal muscle activity. A notion is that the SR dysfunction in Ca2+ transport is one of the causative factors of skeletal muscle fatigue. However the precise mechanisms that mediate skeletal muscle fatigue have yet to be identified.There have been many investigations on the functional aspects of SR from skeletal muscle after activity including electrical stimulation, exercising training and fatigue or a bout of prolonged or exhaustive exercising. However there exist considerable differences among results due to tested fiber type (slow- or fast-twitch muscle), activation pattern (electrical stimulation, endurance training, a bout of prolonged exercise and exhaustion, et at.), duration of activity, and numerous environmental factors In general competitive athletes in endurance events adopt the training pattern increasing duration and/or intensity. The athletic performance improves after an estabilishment of new physiological balance between training and muscular functional status. How are SR activities in Ca2+ uptake, release and Ca2+-ATPase under the kind of training, and whether some nutrients play a role in regulating changed SR function in vitro. Seldom effort on the function of SR from skeletal muscle of endurance training or exhaustion is involved in methodological combination between biochemical and molecular biological approaches At the present. Considering the importance of SR function in normal muscular activity, It may be of potential significance in investigating the blood biochemical indicators that may reflect or value intrinsic SR Ca2+ transport alterations after muscular activity Because muscle biopsy has possible damaging effect and relative inconvenience, and can not easily be accepted by athletes.According to the consideration above, the present study investigated the functional changes of SR from rat skeletal muscle (quadriceps and gastrocnemius) after six weeks of progressively time-increasing swimming training load. In addition we tested the levels of calmodulin (CaM) and cAMP, which can regulate the activity of Ca2+-ATPase and Ca2+ release channels through their direct or indirect phospharylating enzymes or channels, in quadriceps. Serum testosterone, creatine kinase (CK) and RBC ATPase activity were determined to aim at the relationships between these biochemical parameters and muscle SR Ca2+-ATPase activity, Ca2+ uptake and release. We also observed in vitro effects oftaurine and L-glutamine addition on SR Ca2+ transport.The results are shown in attached table. In addition to these, the levels in serum testosterone, CK and RBC ATPase activity were proved to be closely associated with rat functional status. RBC ATPase activity demonstrated the significantly negative relation to some extent with SR Ca2+ transport activity. Swimming time to exhaustion demonstrated significantly or marginal positive relation with SR Ca2+-ATPase and Ca2+-Mg2+-ATPase, Ca2+ uptake and release. The results showed the most changed extent for SR Ca2' transport, CaM and cAMP levels in quadriceps, serum testosterone and CK activity in trained exhausted rat.The results indicated that improved performance of rat after six weeks of progressively time-increasing swimming endurance training was closely related to enhanced SR capacity in the maintenance of Ca2+ turnover during skeletal muscular activity. The mechanisms of enhanced SR capacity may be involved in synergetic regulatory effect of CaM and cAMP on SR Ca2+ transport, and may be related to the slightly increased SERCA2a gene expression in gastrocnemius SR from trained exhausted rat. Increased RBC ATPase activity after exhaustion may be related to increase...