Duchateau J, Hainaut K
J Muscle Res Cell Motil. 1986 Feb;7(1):18-24. doi: 10.1007/BF01756198.
Nonlinear summation of contractions is studied in single barnacle (Balanus nubilus) muscle fibres, loaded with the photoprotein aequorin. The results indicate that nonlinear summation of aequorin transients is indeed present and for short interpulse intervals (25-250 ms), a more-than-linear summation of transients, which suggest an increase of the cytosolic Ca2+ concentration in the second response, is observed. This augmented Ca2+ concentration is not merely due to summation with the preceding conditioning transient, but to an enlargement of the second transient in its own right. Furthermore, the enlargement of the second Ca2+ response is not the result of prolonged release, or slowing of re-uptake by intracellular organelles. On the contrary, Ca2+ release is found to be enhanced and for short depolarizations (20 ms), its time to half re-uptake is reduced. The intensified Ca2+ release, triggered by the second standard depolarization, is related to the level of cytosolic Ca2+ concentration reached in the conditioning response and, for example, appears to be larger in the presence of Dantrolene-sodium, which is known to reduce Ca2+ movements in a single twitch. It is concluded that contractile potentiation observed during nonlinear summation of contractions, is associated with a potentiation of intracellular Ca2+ movements, which interact to regulate the cytosolic Ca2+ concentration during contraction.
在装载了光蛋白水母发光蛋白的单个藤壶（Balanus nubilus）肌纤维中研究了收缩的非线性总和。结果表明，水母发光蛋白瞬变的非线性总和确实存在，并且对于短脉冲间隔（25 - 250毫秒），观察到瞬变的超线性总和，这表明在第二次反应中胞质Ca2+浓度增加。这种增加的Ca2+浓度不仅仅是由于与先前的条件瞬变总和，而是由于第二个瞬变本身的扩大。此外，第二个Ca2+反应的扩大不是延长释放或细胞内细胞器再摄取减慢的结果。相反，发现Ca2+释放增强，并且对于短去极化（20毫秒），其再摄取到一半的时间减少。由第二个标准去极化触发的增强的Ca2+释放与条件反应中达到的胞质Ca2+浓度水平有关，例如，在已知会减少单个抽搐中Ca2+运动的丹曲林钠存在的情况下，它似乎更大。得出的结论是，在收缩的非线性总和期间观察到的收缩增强与细胞内Ca2+运动的增强有关，这些运动在收缩过程中相互作用以调节胞质Ca2+浓度。
