Bittar E E, Nwoga J
Comp Biochem Physiol C Comp Pharmacol Toxicol. 1984;78(1):89-98. doi: 10.1016/0742-8413(84)90052-5.
A study has been made of the effect of microinjected cholera toxin (CT) on the efflux in single barnacle muscle fibers. Characteristically, injected CT causes sustained stimulation of the ouabain-insensitive Na efflux but only after a lag phase. An effect is seen with as little as a 10(-7) M-solution of CT. Sustained stimulation after a lag phase is also seen following injection of subunit A fragment. Enrichment of fibers with NAD+ fails to enhance the response to CT. Prior injection of GTP or its non-hydrolyzeable analogue, Gpp(NH)p, markedly reduces the response to CT, whilst prior injection of CT reduces the response to guanine nucleotides. Evidence is also brought forward that omission of external Ca2+ reversibly reduces the response to CT and that pre- or postinjection of EGTA markedly reduces the response to CT. In addition, fibers preinjected with CT show increased aequorin light emission. Whereas verapamil and Cd2+ are ineffective, both Mg2+ and trace metals, e.g. Fe and Zn, reverse the response to CT following injection. Prior injection of protein kinase inhibitor reduces the response to CT. As for calmodulin inhibitors, e.g. chlorpromazine, imipramine and mepacrine, they are effective in reducing the response to CT but not calmodulin antibody (IgG). Collectively, the above results are compatible with the view that sustained stimulation of the ouabain-insensitive Na efflux by injected CT is due to persistent activation of adenylate cyclase by the toxin and that a fall in myoplasmic pCa facilitates or augments this activation mechanism.
一项关于微量注射霍乱毒素（CT）对单个藤壶肌纤维外流影响的研究已开展。典型地，注射的CT仅在延迟期后才会引起哇巴因不敏感的钠外流的持续刺激。低至10⁻⁷M的CT溶液就能产生这种效应。注射亚基A片段后也会出现延迟期后的持续刺激。用NAD⁺富集纤维并不能增强对CT的反应。事先注射GTP或其不可水解类似物Gpp(NH)p会显著降低对CT的反应，而事先注射CT则会降低对鸟嘌呤核苷酸的反应。还有证据表明，去除细胞外Ca²⁺会可逆地降低对CT的反应，而注射EGTA前后都会显著降低对CT的反应。此外，预先注射CT的纤维会显示水母发光蛋白的发光增加。维拉帕米和Cd²⁺无效，而Mg²⁺和微量金属（如Fe和Zn）在注射后会逆转对CT的反应。事先注射蛋白激酶抑制剂会降低对CT的反应。至于钙调蛋白抑制剂，如氯丙嗪、丙咪嗪和甲哌卡因，它们能有效降低对CT的反应，但钙调蛋白抗体（IgG）则无效。总体而言，上述结果与以下观点一致：注射的CT对哇巴因不敏感的钠外流的持续刺激是由于毒素对腺苷酸环化酶的持续激活，并且肌浆中pCa的下降促进或增强了这种激活机制。
