21.　高機械負荷における心室乳頭筋被動張力の増加による筋弛緩期の延長 | The force enhancement extended relaxation cycle in high preload cardiac papillary muscle

一般演題4

21.　高機械負荷における心室乳頭筋被動張力の増加による筋弛緩期の延長

尹　敏¹，Annie Christel Bell¹，樊　守艳²，Joseph Akparibila Azure¹，陈　志斌²，高　凌峰²，王　杨²

¹海南医学院国際教育スクールMB BChセクション
²特殊環境スポーツ医学生理科学実験室

The force enhancement extended relaxation cycle in high preload cardiac papillary muscle

Min Yin¹, Annie Christel Bell¹, Shouyan Fan², Joseph Akparibila Azure¹, Zhibin Chen², Lingfeng Gao², Yang Wang²

¹Section of Medicinae Baccalaureus Baccalaureus Chirurgiae, International Education School
²Laboratory of Extreme Sports Medicine and Physiology Sciences, Hainan Medical College

【Aim】　The active stretch caused passive tension was included an amplitude ascending and a subsequent tension attenuation.　A myogenic spontaneous force enhancement was a significant waveform in the attenuation phase as a result of secondary sustained static stretch of the muscle. This force enhancement extended an inotropic effect during cardiac muscle relaxation.　We investigated the force enhancement in mice cardiac papillary muscle under the high preload condition.
【Method】　The cardiac papillary muscle bundle were isolated from Kunming mice ventricle.　Preparations were bath in Ringer's solution and stretched to 20% of its initial length to obtain the low preload condition, further adjusted to 40% of its length to maintain a high preload condition.　The preparations were active stretched to obtain an ascending of passive tension, subsequently to have an attenuation of the tension.　An enhancement force were generated in the attenuation phase under the high preload condition.　For evaluating extracellular Ca²⁺ in the influence on the enhancement, preparations were stretched in Nifedipine intervene or in 0.9% saline solution. The force enhancement properties, especially in 1^st and 2^nd stretch under the high condition were traced and evaluated.
【Results】　The force enhancement generated during the sustained static stretch, is one kind of isometric myogenic spontaneous tension.　The amplitude of the enhancive force were regard with preload and extracellular Ca²⁺ conditions. In high preload preparation, 580% increasing of force enhancement in 2^nd stretch were recognized, while the attenuated phase were extended 23% on the time scale （6,327.49±524.52 mg to 1,091.71±491.25 mg of the amplitude, 117.42±34.80 msec to 75.08±8.31 msec of the attenuated phase, in 2^nd and 1^st stretch respectively）.　In Ca²⁺ rich solution, force enhancement amplitude were exceeded its maximum passive tension in 2^nd stretch, however this were not generated in 0.9% saline rinsed and Nifedipine intervened preparation.　2^nd stretch induced attenuation phase on time line were significantly extended in Ringer's solution and 0.9% saline solution.
【Conclusion】　Under the high preload condition, force enhancement amplitude were influenced by extracellular Ca²⁺.　However force enhancement extension on the time scale were not interrupted by extracellular Ca²⁺, but more affected by its amplitude.　The force enhancement prolonged the passive tension on time scale, thus extended the relaxation period.　As the conclusion, the enhancement force amplitude and extension time significantly disrupted the isotropic effect in relaxation phase of the cardiac papillary muscle.　The myogenic spontaneous force enhancement induced prolongation of the passive tension on the time scale further delayed the onset of contraction.　This model is useful for mimic and the studying physiological effects of overweight or microgravity in cardiac cycle and blood pumping.