Akasu T, Gallagher J P, Hirai K, Shinnick-Gallagher P
J Physiol. 1986 May;374:457-73. doi: 10.1113/jphysiol.1986.sp016091.
The effect of vasoactive intestinal polypeptide (VIP) on the neuronal membranes of isolated cat vesical pelvic ganglia and its underlying ionic mechanism were examined by means of intracellular recording and voltage-clamp techniques. Application of VIP (0.05-50 microM) to the neurones by pressure 'puff' ejection through a micropipette placed close to the neurones produced a depolarizing response (2-15 mV) in 83% of neurones tested; this effect was concentration dependent. The VIP-induced depolarization frequently evoked spontaneous action potentials in quiescent neurones and increased the frequency of action potentials in spontaneously firing neurones. The VIP depolarization was not blocked in a Ca2+-free, high-Mg2+ solution or in a solution containing hexamethonium (1 mM) and atropine (1 microM). Tetrodotoxin (TTX; 1 microM) also did not affect the VIP depolarization. The VIP depolarization was associated with an increase in membrane resistance and the slope of a current-voltage relation (I-V curve) was increased by VIP. Conditioning hyperpolarization and depolarization of the membrane increased and decreased the amplitude of the VIP depolarization, respectively. The VIP depolarization reversed polarity around--100 mV. The reversal potential shifted about 20 mV to a more positive level in a high-K+ (10 mM) solution in accord with the Nernst equation. Substituting Cl- with isethionate in the superfusate did not affect the reversal potential of the VIP depolarization. Closure of M-channels does not underlie VIP action since the VIP depolarization was enhanced by muscarine (10 microM) and unchanged in the presence of Ba (5 mM), or intracellular or extracellular Cs+, conditions known to block the M-channels (Adams, Brown & Constanti, 1982a, b). Tetraethylammonium (TEA; 20 mM) also did not affect the VIP depolarization. Voltage-clamp analyses showed that VIP applied by pressure ejection produced an inward current of 80-110 pA associated with a decrease in membrane conductance (from 2.8 to 3.5 nS) at a holding potential of--60 mV. VIP inward current was diminished by either repetitive or continuous application of VIP (5 microM) suggesting desensitization of the VIP receptor. It is concluded that VIP produces a depolarization in neurones of bladder parasympathetic ganglia by decreasing a K+ conductance, the pharmacological characteristics of which are unlike previously described K+ conductance mechanisms.
采用细胞内记录和电压钳技术，研究了血管活性肠肽（VIP）对离体猫膀胱盆神经节神经元膜的作用及其潜在的离子机制。通过靠近神经元放置的微吸管以压力 “吹注” 的方式将VIP（0.05 - 50 μM）施加于神经元，在83% 的受试神经元中产生了去极化反应（2 - 15 mV）；这种效应呈浓度依赖性。VIP诱导的去极化经常在静息神经元中引发自发动作电位，并增加自发放电神经元的动作电位频率。在无Ca2 +、高Mg2 +溶液或含有六甲铵（1 mM）和阿托品（1 μM）的溶液中，VIP诱导的去极化并未被阻断。河豚毒素（TTX；1 μM）也不影响VIP诱导的去极化。VIP诱导的去极化与膜电阻增加相关，并且VIP使电流 - 电压关系（I - V曲线）的斜率增大。对膜进行预处理的超极化和去极化分别增加和降低了VIP诱导的去极化幅度。VIP诱导的去极化在约 - 100 mV处极性反转。根据能斯特方程，在高K +（10 mM）溶液中，反转电位向更正的水平移动了约20 mV。用羟乙基磺酸替代灌流液中的Cl - 并不影响VIP诱导的去极化的反转电位。由于毒蕈碱（10 μM）增强了VIP诱导的去极化，并且在已知可阻断M通道的Ba（5 mM）、细胞内或细胞外Cs + 存在的情况下，该去极化未发生变化（Adams、Brown和Constanti，1982a，b），因此M通道的关闭不是VIP作用的基础。四乙铵（TEA；20 mM）也不影响VIP诱导的去极化。电压钳分析表明，通过压力喷射施加的VIP在 - 60 mV的钳制电位下产生了80 - 110 pA的内向电流，同时伴有膜电导降低（从2.8降至3.5 nS）。重复或持续施加VIP（5 μM）会使VIP内向电流减小，提示VIP受体脱敏。结论是，VIP通过降低K + 电导使膀胱副交感神经节神经元去极化，其药理学特性不同于先前描述的K + 电导机制。
