Effects of cyanide on a cation channel and catecholamine secretion

用制霉菌素法记录了豚鼠肾上腺嗜铬细胞的全细胞电流。应用5 mM氰化物可逆地产生内向电流，在负膜电位下没有明显延迟。在100%氮气饱和的低氧溶液中加入0.5mMNa_2S_2O_4，也能产生类似的电流。氰化物诱导的电流不受影响的取代蔗糖与葡萄糖。结果表明，氰化物的作用是由于化学缺氧引起的，氰化物电流的反转电位为-24 mV，电流-电压关系在-50 mV以下有一个负斜率区，这些特征与毒蕈碱受体诱导的非选择性阳离子（NS）电流相似。为了阐明是否暴露于氰化物引起的儿茶酚胺分泌，从一个单一的嗜铬细胞释放的儿茶酚胺测定电流。应用氰化物和毒蕈碱都能引起儿茶酚胺的分泌，而用Mg^2+取代浴中的Ca^2+离子或应用电压依赖性Ca^2+通道阻断剂Cd ^2+和D-600则能消除这种分泌。毒蕈碱和氰化物诱导的去极化伴随着强烈的放电，并增加了细胞内Ca^2+浓度，用Ca^2+指示剂Fluo-3 AM以外部Ca^2+依赖的方式测量。从这些结果中，我们得出结论，毒蕈碱和氰化物或化学性缺氧通过去极化和随后的电压依赖性Ca^2+通道的激活引起儿茶酚胺分泌，并且去极化至少部分是由于NS通道的激活。

The whole-cell current in an isolated adrenal chromaffin cell of guinea pig was recorded with the Nystatin method. Application of 5 mM cyanide reversibly produced an inward current without a noticeable delay at negative membrane potentials. A similar current was elicited by exposure to hypoxic solution, which was saturated with 100% nitrogen gas and 0.5mM Na_2S_2O_4 was added to. The cyanide-induced current was not affected by replacement of sucrose with glucose. The results indicate that the effect of cyanide is due to chemical hypoxia The reversal potential of the cyanide current was -24 mV and the current voltage relationship had a negative slope region below -50mV.These characteristics of the cyanide current were similar to those of the muscarinic receptor-induced nonselective cation (NS) current. To elucidate whether exposure to cyanide evokes catecholamine secretion, catecholamine released from a single chromaffin cell was measured with amperometry. Application of cyanide and of muscarine both evoked catecholamine secretion, and this secretion was abolished by replacement of bath Ca^<2+> ions with Mg^<2+> or by application of the voltage-dependent Ca^<2+> channel blockers, Cd^<2+> and D-600. Muscarine and cyanide induced depolarization with a robust of firings and increased intracellular Ca^<2+> concentrations measured with the Ca^<2+> indicator Fluo-3 AM in a external Ca^<2+>-dependent manner. From these results, we conclude that muscarine and cyanide or chemical hypoxia evoke catecholamine secretion through depolarization and the subsequent activation of voltage-dependent Ca^<2+> channels and that the depolarization is at least in part due to activation of NS channels.