Matsumoto M, Riker W K
J Pharmacol Exp Ther. 1983 Oct;227(1):16-21.
Synaptic transmission in the isolated bullfrog sympathetic ganglion was studied during graded reductions in extracellular Ca++, from the normal of 1.8 mM, in the absence and in the presence of different concentrations of 3,4-diaminopyridine (3,4-DAP). In drug-free Ringer's synaptic transmission, measured as the amplitude of the postganglionic compound action potential, failed progressively as Ca++ was reduced from 1.8 to 0.47 mM. This Ca++-dependence curve of synaptic transmission was shifted to the left (lower Ca++) by 3,4-DAP in dose-related fashion with threshold at 0.1 microM and maximum shift at 10 microM 3,4-DAP. At maximum shift (4- to 5-fold) in the Ca++-dependence curve, compound action potential amplitude was normal at 0.33 mM Ca++ then failed progressively as Ca++ was reduced to 0.12 mM. Also 3,4-DAP causes stimulus-bound repetitive postganglionic responses (SBR) to single preganglionic stimuli (Apatoff and Riker, 1982). SBR were selectively abolished as Ca++ was reduced form 1.8 to 0.47 mM. The data reveal that 3,4-DAP facilitates presynaptic influx or binding of Ca++. Furthermore, the high Ca++ requirement for 3,4-DAP-induced SBR, as well as the difference between threshold drug concentrations for preserving transmission (0.1 microM) and for generating SBR (2-5 microM), lead to the speculation that there may be two presynaptic receptors for 3,4-DAP.
在细胞外钙离子浓度从正常的1.8 mM逐步降低的过程中，研究了分离的牛蛙交感神经节中的突触传递，实验分别在不存在和存在不同浓度的3,4 - 二氨基吡啶（3,4 - DAP）的情况下进行。在无药物的林格氏液中，以节后复合动作电位的幅度来衡量突触传递，当钙离子浓度从1.8 mM降低到0.47 mM时，突触传递逐渐失效。3,4 - DAP使这种突触传递的钙离子依赖性曲线以剂量相关的方式向左（更低的钙离子浓度）移动，阈值为0.1 microM，在10 microM 3,4 - DAP时移动最大。在钙离子依赖性曲线最大移动时（4至5倍），在0.33 mM钙离子浓度下复合动作电位幅度正常，然后随着钙离子浓度降低到0.12 mM而逐渐失效。此外，3,4 - DAP会引发对单个节前刺激的刺激束缚性节后重复反应（SBR）（阿帕托夫和里克，1982年）。当钙离子浓度从1.8 mM降低到0.47 mM时，SBR被选择性消除。数据表明，3,4 - DAP促进突触前钙离子的内流或结合。此外，3,4 - DAP诱导SBR对钙离子的高需求，以及维持传递（0.1 microM）和产生SBR（2 - 5 microM）的药物阈值浓度之间的差异，引发了一种推测，即3,4 - DAP可能存在两种突触前受体。
