The effect of cooling on in vivo intracellular calcium ion concentration ([Ca²⁺]i) after eccentric contractions (ECs) remains to be determined. We tested the hypothesis that cryotherapy following ECs promotes an increased [Ca²⁺]i and induces greater muscle damage in two muscles with substantial IIb and IIx fiber populations. The thin spinotrapezius (SPINO) muscles of Wistar rats were used for in vivo [Ca²⁺]i imaging and tibialis anterior (TA) muscles provided greater fidelity and repeatability of contractile function measurements. SPINO [Ca²⁺]i was estimated using fura 2-AM and the magnitude, location and temporal profile of [Ca²⁺]i determined as the temperature near the muscle surface post-ECs was decreased from 30^oC (control) to 20^oC or 10^oC. Subsequently, in the TA the effect of post-ECs cooling to 10^oC on muscle contractile performance was determined at 1 and 2 days after ECs. TA muscle samples were examined by hematoxylin and eosin staining to assess damage. In SPINO reducing the muscle temperature from 30^oC to 10^oC post-ECs resulted in a 3.7-fold increase in the spread of high [Ca²⁺]i sites generated by ECs (P<0.05). These high [Ca²⁺]i sites demonstrated partial reversibility when rewarmed to 30^oC. Dantrolene, a ryanodine receptor Ca²⁺ release inhibitor, reduced the presence of high [Ca²⁺] sites at 10^oC. In the TA cooling exacerbated ECs-induced muscle strength deficits post-ECs via enhanced muscle fiber damage (P<0.05). By demonstrating that cooling post-ECs potentiates [Ca²⁺]i derangements, this in vivo approach supports a putative mechanistic basis for how post-exercise cryotherapy might augment muscle fiber damage and decrease subsequent exercise performance.

中文翻译：

---

大鼠骨骼肌偏心收缩后冷却过程中的体内Ca ²⁺动态

偏心收缩（ECs）后冷却对体内细胞内钙离子浓度（[Ca ²⁺ ] i）的影响尚待确定。我们测试了以下假设，即EC后的冷冻疗法可促进[Ca ²⁺ ] i的增加，并在具有大量IIb和IIx纤维群的两条肌肉中引起更大的肌肉损伤。Wistar大鼠的稀疏棘肌（SPINO）肌肉用于体内[Ca ²⁺ ] i成像，胫骨前（TA）肌肉提供了更高的保真度和收缩功能测量的可重复性。使用呋喃2-AM和[Ca ²⁺的大小，位置和时间剖面]估算了SPINO [Ca ²⁺ ] i] i的确定为肌肉表面后的EC从30降低附近的温度^Ô C（控制），以20 ^ö C或10 ^Ò ℃。随后，在TA后的EC的冷却至10的效果^Ò C对肌肉收缩ECs后1天和2天确定性能。通过苏木精和曙红染色检查TA肌肉样品以评估损伤。在SPINO中，将EC后的肌肉温度从30 ^o C降低到10 ^o C，导致EC产生的高[Ca ²⁺ ] i部位的扩散增加了3.7倍（P <0.05）。这些高[Ca ²⁺ ] i位点重新加热至30 ^o时显示出部分可逆性^。C. Dantrolene，一种ryanodine受体Ca ²⁺释放抑制剂，在10 ^o C时减少了高[Ca ²⁺ ]位的存在。在TA冷却中，ECs通过增强的肌纤维损伤加剧了ECs引起的肌力不足（P <0.05）。通过证明冷却后EC会增强[Ca ²⁺ ] i错位，这种体内方法为运动后冷冻疗法如何增加肌纤维损伤并降低随后的运动表现提供了推测的机械基础。