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Calcium sensitivity during staircase with sequential incompletely fused contractions
Journal of Muscle Research and Cell Motility ( IF 1.8 ) Pub Date : 2020-01-08 , DOI: 10.1007/s10974-019-09572-4
Lisa D Glass 1 , Arthur J Cheng 2, 3 , Brian R MacIntosh 1
Affiliation  

Activity dependent potentiation is thought to result from phosphorylation of the regulatory light chains of myosin, increasing Ca2+ sensitivity. Yet, Ca2+ sensitivity decreases early in a period of intermittent contractions. The purpose of this study was to investigate the early change in Ca2+ sensitivity during intermittent submaximal tetanic contractions. Flexor digitorum brevis muscle fibres were dissected from mice after cervical disarticulation. Fibres were superfused with Tyrode solution at 32 °C. Length was set to yield maximal tetanic force. Indo-1 was microinjected into fibres and allowed to dissipate for 30 min. Fluorescence was measured at 405 and 495 nm wavelength and the ratio was used to estimate [Ca2+]. A control force-Ca2+ relationship was determined with stimulation over a range of frequencies, yielding constants for slope, max force, and half-maximal [Ca2+] (pCa2 +50). Data were collected for sequential contractions at 40 Hz at 2 s intervals. Active force decreased over the first 1–4 contractions then increased. A force-pCa2+ curve was fit to each contraction, using the control values for the Hill slope and max force by adjusting pCa2+50 until the curve passed through the target contraction. Data are presented for three contractions for each fibre: first, maximum shift to the right, and last contraction. There was a significant shift to the right for pCa2+50 (decreased Ca2+ sensitivity), usually early in the series of intermittent contractions, then pCa2 +50 shifted to the left, but remained significantly different from the control value. Although potentiation is associated with increased Ca2+ sensitivity, this increase begins only after Ca2+ sensitivity has decreased and, in most cases, Ca2+ sensitivity does not increase above the control level.



中文翻译:

楼梯间连续不完全融合收缩时的钙敏感性

活性依赖性增强被认为是由肌球蛋白调节轻链的磷酸化引起的,增加了 Ca 2+敏感性。然而,Ca 2+敏感性在间歇性收缩期早期降低。本研究的目的是调查间歇性次最大强直性收缩期间Ca 2+敏感性的早期变化。在颈椎离断后从小鼠中解剖出趾短屈肌纤维。在 32°C 下用 Tyrode 溶液灌注纤维。长度设置为产生最大强直力。Indo-1 被显微注射到纤维中并使其消散 30 分钟。在 405 和 495 nm 波长处测量荧光,并且该比率用于估计 [Ca 2+]。控制力-Ca 2+关系通过在一定频率范围内的刺激来确定,产生斜率、最大力和半最大值[Ca 2+ ] (pCa 2 + 50 ) 的常数。以 40 Hz 的频率以 2 秒的间隔收集连续收缩的数据。主动力在前 1-4 次收缩时减少,然后增加。力-pCa 2+曲线适合每次收缩,使用希尔斜率和最大力的控制值,通过调整 pCa 2+ 50直到曲线通过目标收缩。提供了每种纤维的三种收缩的数据:第一次,最大向右移动,最后一次收缩。pCa 2+右移显着50(降低 Ca 2+敏感性),通常在一系列间歇性收缩的早期,然后 pCa 2 + 50向左移动,但仍与对照值显着不同。尽管增强与 Ca 2+敏感性增加有关,但这种增加仅在 Ca 2+敏感性降低后才开始,并且在大多数情况下,Ca 2+敏感性不会增加到高于对照水平。

更新日期:2020-01-08
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