The Effect Of Ca2+/CaN Singal Way On Fiber Type Composition In Unloading And Reloading Rats

Purpose:the aim of this study is to investigate the effects of Ca2+/calcineurin (CaN) signaling pathway in the changes of skeletal muscle fiber type and cross section area during hindlimb unloading and reloading.Methods:Thirty female Sprague-Dawley rats were randomly assigned to five groups:control group (CON),14D tail-suspension group(TS),14D tail-suspension following 14D normal rehabilitation group(NR),14D tail-suspension following 14D eccentric exercise rehabilitated group(ER),14D tail-suspension following 14D eccentric exercise and injected Cyclosporin A rehabilitation (ER+CsA). Gastroenemius were were harvested at the first 14Ds and the second 14Ds, The proportion of myosin heavy chain (MHC) isoforms and cross sectional area of fibers by SDS-PAGE silver stained approach and ATPase staining. CaN, [Ca2+]i, Ca2+-ATPase activity as well as Ca2+' uptake and relaxed by colorimetry. Slow-MHC, fast-MHC protein content by Western blotting were performed. The cross ectional area (CSA) and the proportion of typeⅠⅡa andⅡb fibers were measured using Leica image analysis system.Result:1, In TS, wet weights of the gastroenemius, CSA of typeⅠandⅡb fibers, and proportion of typeⅠandⅡa fibers decreased obviously, as compared with those rats in CON (P＜0.01).Ⅰ,Ⅱa andⅡb type CSA were reduced 42.2%,30.0%,17.9%. Re-loading 14 days, ER group'Ⅰtype CSA returned to CON levels; for typeⅡa, three kinds of re-loading a way return to or exceed CON level; in order toⅡb, NR group and the ER group CSA restored to 113.3% and 111.5% group CON level (P＜0.05), ER+CsA group back to the CON group levels, with the NR and ER groups significantly different (P＜0.05).2, Using ATPase staining and gel electrophoresis with silver staining of gastrocnemius muscle fiber type of comparative analysis of changes in the composition, toⅠandⅡa type,reducing the proportion (22.2% vs 27.3%; 26.0% vs 16%),Ⅱb significantly increased (27.2% vs 24.9%); and then reloading, the ER+CsA Recovery GroupⅡa type further decline (compared with the control group decreased by 30.9% vs 18.8%), IIbis still at a high level, (higher than the control group, 18.1% vs 33.9%).3, Compared with the CON group, TS group gastrocnemius muscle slow-MHC protein expression decreased significantly (P＜0.05). Under different conditions and then load for 14 days, with the CON group and NR group compared, ER group and ER+CsA group of slow-MHC were significantly reduced (P＜0.05); compared with the CON group, ER group and ER+CsA group of fast-MHC decreased significantly (P＜0.05).Conclusion:1, under 14 unloading, gastrocnemius occurs disuse atrophy, I type go to load based on the most sensitive and prone to slow muscle disuse atrophy.2, After reloading, eccentric exercise activated Ca2+, and promote CaN regulating muscle fiber type and muscle fiber hypertrophy.3, PI3K/PKB and GSK-3βinvolved in Ca2+/CaN regulating muscle fiber hypertrophy, muscle fiber types as to whether to participate more in-depth study has yet to be transformed.