Maeno T, Hara N
Department of Physiology, Shimane Medical University, Izumo, Japan.
Acta Physiol Pharmacol Latinoam. 1989;39(4):375-82.
To elucidate the role of intracellular Ca ions in neuromuscular transmission, we investigated using frog neuromuscular preparations the effect of 1,2-bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid (BAPTA) on frequency augmentation-potentiation (formerly frequency facilitation), which have been shown to be useful in identifying the sites of actions of various cholinergic agents. Buffering of intracellular Ca ions by BAPTA was found to suppress only Ca-dependent component of frequency augmentation-potentiation (mo); its stimulation frequency dependent factor (k) remained unaffected. Depression by BAPTA treatment of the short-term facilitation of endplate potential (EPP) was the same in both the resting and augmented states. However, the effect of BAPTA was antagonized, but only partially, with the administration of Ca-ionophore, A23187. These suggest that Ca-buffering capability of the intracellularly loaded BAPTA was maintained during low frequency repetitive stimulation. In addition, the post-tetanic potentiation of miniature EPP frequency in Ca-free EGTA Ringer was practically unaffected with BAPTA treatment. Undoubtedly Ca ions were essential for transmitter release and short-term facilitation, but Ca ions were not solely responsible for all the changes of transmitter release. The contribution of transmitter mobilization to maintaining the synaptic transmission during repetitive stimulation should be reevaluated.
为阐明细胞内钙离子在神经肌肉传递中的作用，我们使用青蛙神经肌肉标本研究了1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸（BAPTA）对频率增强-增强作用（原频率易化）的影响，该作用已被证明有助于确定各种胆碱能药物的作用位点。发现BAPTA对细胞内钙离子的缓冲仅抑制频率增强-增强作用（mo）的钙依赖成分；其刺激频率依赖因子（k）不受影响。BAPTA处理对静息和增强状态下终板电位（EPP）短期易化的抑制作用相同。然而，通过给予钙离子载体A23187，BAPTA的作用被拮抗，但只是部分拮抗。这些结果表明，在低频重复刺激期间，细胞内加载的BAPTA的钙缓冲能力得以维持。此外，在无钙EGTA林格液中，BAPTA处理对微小EPP频率的强直后增强作用实际上没有影响。毫无疑问，钙离子对于递质释放和短期易化是必不可少的，但钙离子并非是递质释放所有变化的唯一原因。在重复刺激期间，递质动员对维持突触传递的贡献应重新评估。
