Abstract：
Unlike in the Cnidaria, where muscle cells are coupled together into an epithelium, ctenophore muscles are single, elongated, intramesogleal structures resembling vertebrate smooth muscle. Under voltage-clamp, these fibers can be separated into different classes with different sets of membrane ion channels. The ion channel makeup is related to the muscle\'s anatomical position and specific function. For example, Beroe ovata radial fibers, which are responsible for maintaining the rigidity of the body wall, generate sequences of brief action potentials whereas longitudinal fibers, which are concerned with mouth opening and body flexions, often produce single longer duration action potentials.Beroe muscle contractions depend on the influx of Ca2+. During an action potential the inward current is carried by Ca2+, and the increase in intracellular Ca2+ concentration generated can be monitored in FLUO-3-loaded cells. Confocal microscopy in line scan mode shows that the Ca2+ spreads from the outer membrane into the core of the fiber and is cleared from there relatively slowly. The rise in intracellular Ca2+ is linked to an increase in a Ca2+-activated K+ conductance (KCa), which can also be elicited by iontophoretic Ca2+ injection. Near the cell membrane, Ca2+ clearance monitored using FLUO3, matches the decline in the KCa conductance. For light loads, Ca2+ is cleared rapidly, but this fast system is insufficient when Ca2+ influx is maintained. Action potential frequency may be regulated by the slowly developing KCa conductance.
摘要：
与Cnidaria不同，肌肉细胞耦合在一起成为上皮，盘虫肌肉是单一的，细长的，类似于脊椎动物平滑肌的脑膜内结构。在电压钳下，这些纤维可以用不同组的膜离子通道分成不同的类别。离子通道组成与肌肉的解剖位置和特定功能有关。例如,Beroeovata放射状纤维，负责保持车身壁的刚度，产生短暂的动作电位序列，而纵向纤维，与张嘴和身体弯曲有关，经常产生单一持续时间较长的动作电位。Beroe肌肉收缩取决于Ca2的流入。在动作电位期间，内向电流由Ca2+携带，并且可以在负载FLUO-3的细胞中监测产生的细胞内Ca2+浓度的增加。线扫描模式中的共聚焦显微镜显示Ca2+从外膜扩散到纤维的芯中并且相对缓慢地从那里清除。细胞内Ca2+的增加与Ca2+激活的K+电导(KCa)的增加有关,也可以通过离子电渗Ca2注射引起。在细胞膜附近，使用FLUO3监测的Ca2+清除与KCa电导的下降相匹配。对于轻负载，Ca2+迅速清除，但是当Ca2+流入被维持时,这种快速系统是不够的。动作电位频率可以通过缓慢发展的KCa电导来调节。
