Godt R E, Kirby A C, Gordon A M
Am J Physiol. 1984 Jan;246(1 Pt 1):C148-53. doi: 10.1152/ajpcell.1984.246.1.C148.
The influence of solution hypertonicity on contraction was studied in small bundles of tonic muscle fibers from the iliofibularis muscle of the frog Rana pipiens. Muscles were activated with high-K+ solutions that had osmolalities which were increased with tris(hydroxymethyl)aminomethanepropionate. Peak potassium contracture force decreased monotonically with tonicity and was zero in solutions with 2.5 or 3 times the osmolality of control Ringer. Contracture force at all tonicities studied (less than or equal to 3 X Ringer) was increased by increasing Ca2+ in the media 10-fold (to 20 mM) and/or by adding caffeine (10-20 mM). Nevertheless, this potentiated force also was diminished as tonicity increased. Force of single, mechanically skinned tonic fibers taken from these bundles was activated by Ca2+ over the same concentration range as that of twitch fibers. Moreover, maximal Ca2+-activated force, normalized per cross-sectional area, was similar in skinned tonic and twitch fibers. As was shown previously in twitch fibers, maximal Ca2+-activated force was decreased when ionic strength was increased. These data suggest that, as with twitch fibers, increased tonicity depresses contraction of tonic fibers by increasing the intracellular ionic strength, which in turn inhibits the ability of the contractile apparatus to generate force. Unlike twitch fibers, however, disruption of the excitation-contraction coupling process probably plays a more significant role in the action of hypertonicity on tonic fibers.
在豹蛙（Rana pipiens）髂腓肌的强直肌纤维小束中，研究了溶液高渗对收缩的影响。用高钾溶液激活肌肉，这些溶液的渗透压随着三（羟甲基）氨基甲烷丙酸盐而增加。钾挛缩峰值力随渗透压单调下降，在渗透压为对照林格液2.5倍或3倍的溶液中为零。在所研究的所有渗透压（小于或等于3倍林格液）下，通过将培养基中的Ca2+浓度增加10倍（至20 mM）和/或添加咖啡因（10 - 20 mM），挛缩力会增加。然而，随着渗透压增加，这种增强的力也会减小。从这些肌束中取出的单个机械去皮肤强直纤维的力，在与抽搐纤维相同的Ca2+浓度范围内被激活。此外，按横截面积归一化的最大Ca2+激活力，在去皮肤强直纤维和抽搐纤维中相似。如先前在抽搐纤维中所示，当离子强度增加时，最大Ca2+激活力会降低。这些数据表明，与抽搐纤维一样，渗透压增加通过增加细胞内离子强度来抑制强直纤维的收缩，这反过来又抑制了收缩装置产生力的能力。然而，与抽搐纤维不同的是，兴奋 - 收缩偶联过程的破坏可能在高渗对强直纤维的作用中起更重要的作用。
