Feher J J, Waybright T D, Fine M L
Department of Physiology, Virginia Commonwealth University, Richmond 23298-0551, USA.
J Muscle Res Cell Motil. 1998 Aug;19(6):661-74. doi: 10.1023/a:1005333215172.
The sonic muscle of the oyster toadfish, Opsanus tau, can produce unfused contractions at 300 Hz. Electron microscopy shows a great abundance of the Sarcoplasmic reticulum (SR) in this muscle, but no functional characterization of the capabilities of the SR has been reported. We measured the oxalate-supported Ca2+ uptake rate and capacities of homogenates of toadfish sonic muscle and rat extensor digitorum longus (EDL) muscle, and estimated the number of pump units by titration with thapsigargin, a high-affinity, specific inhibitor of the SR Ca-ATPase. The Ca2+ uptake rate averaged 70.9 +/- 9.5 mumol min -1 per g tissue for the toad fish sonic muscle, and 73.5 +/- 3.7 mumol min -1 g-1 for rat EDL. The capacity for Ca2+ -oxalate uptake was 161 +/- 20 mumol g -1 and 33 +/- 2 mumol g -1 for toadfish sonic muscle and rat EDL, respectively. Thus, the rates of Ca2+ uptake were similar in the two muscles, but the toadfish sonic muscle had about five times the capacity of the rat EDL. The number of pumps as estimated by thapsigargin titration was 68 +/- 4 nmol of Ca-ATPase per g tissue in the toadfish, and 42 +/- 5 nmol Ca-ATPase per g tissue in the rat EDL. The turnover number, defined as the Ca2+ uptake divided by the number of pumps, was 1065 +/- 150 min -1 for toadfish and 1786 +/- 230 min -1 for rat EDL (p < 0.05) at 37 degrees C. The Ca2+ uptake rate of toadfish sonic muscle at 22 degree C, a typical temperature for calling toadfish, averaged 42 +/- 1% of its rate at 37 degree C. At these operating temperatures, the toadfish SR is likely to be slower than the rat fast-twitch SR, yet the toadfish sonic muscle supports more rapid contractions. One explanation for this is that the voluminous SR provides activator Ca2+ for contraction, but the abundant parvalbumin plays a major role in relaxation.
海蟾蜍（Opsanus tau）的发声肌肉能够以300赫兹的频率产生不完全强直收缩。电子显微镜观察显示，该肌肉中肌浆网（SR）非常丰富，但尚未见有关肌浆网功能特性的报道。我们测定了海蟾蜍发声肌肉匀浆和大鼠趾长伸肌（EDL）匀浆的草酸盐支持的Ca2+摄取速率和摄取能力，并用毒胡萝卜素（一种对肌浆网Ca-ATP酶具有高亲和力的特异性抑制剂）滴定法估算了泵单位的数量。海蟾蜍发声肌肉的Ca2+摄取速率平均为每克组织70.9±9.5 μmol·min-1，大鼠EDL为73.5±3.7 μmol·min-1·g-1。海蟾蜍发声肌肉和大鼠EDL的Ca2+-草酸盐摄取能力分别为161±20 μmol·g-1和33±2 μmol·g-1。因此，两种肌肉的Ca2+摄取速率相似，但海蟾蜍发声肌肉的摄取能力约为大鼠EDL的五倍。用毒胡萝卜素滴定法估算的泵数量，海蟾蜍为每克组织68±4 nmol Ca-ATP酶，大鼠EDL为每克组织42±5 nmol Ca-ATP酶。在37℃时，周转率（定义为Ca2+摄取量除以泵数量）海蟾蜍为1065±150 min-1，大鼠EDL为1786±230 min-1（p<0.05）。在22℃（海蟾蜍鸣叫的典型温度）时，海蟾蜍发声肌肉的Ca2+摄取速率平均为其在37℃时速率的42±1%。在这些工作温度下，海蟾蜍的肌浆网可能比大鼠快肌的肌浆网慢，但海蟾蜍发声肌肉却能支持更快的收缩。对此的一种解释是，大量的肌浆网为收缩提供激活Ca2+，但丰富的小清蛋白在舒张过程中起主要作用。
