Actions of barium and rubidium on membrane currents in canine Purkinje fibres.
Actions of barium and rubidium on membrane currents in canine Purkinje fibres.
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钡和铷对犬浦肯野纤维膜电流的作用。
DOI：
10.1113/jphysiol.1983.sp014691
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
Mulrine,NK
中科院分区：
文献类型：
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作者：
Cohen,IS;Falk,RT;Mulrine,NK
研究了本底K+电导阻断剂Ba2+和Rb+的作用。最近对有蹄类浦肯野纤维进行的研究表明，起搏电流是由超极化激活的内向电流。这一假说是基于Ba2+降低内向整流背景K+电导而不影响起搏电流的假设。在泰罗德浴液中加入5 mM-BaCl2可降低背景K+渗透率，并消除起搏电流的反转。当返回到不含Ba2+的泰罗德溶液时，反转现象再次出现。在4 mM-K+Tyrode溶液中，5 mM-BaCl2也使起搏电位正值下的时间依赖电流降低到-95 mV左右。Ba2+Tyrode溶液中的起搏器电流通常不具有指数时间过程，通常呈非单调衰减。它可能需要两分钟以上的时间才能达到稳定状态。膜电流的快速初始成分在浦肯野纤维的起搏电位范围内超极化时观察到，被称为“耗尽电流”，它仍然存在于Ba2+-Tyrode溶液中，但如果在Ba2+-Tyrode溶液中加入10 mM-CsCl2，则会减少或消除这种成分。Cs+的加入伴随着Ba2+-Tyrode溶液中膜电流的外移。Ba2+以剂量依赖的方式降低背景K+通透性。添加0.5至1 mM的BaCl2可获得最大效果。将BaCl2的量提高到这个水平以上，即使没有观察到对背景渗透率的进一步影响，也会降低随时间变化的电流。Rb+对K+的替代降低了起搏电流在正向至-100 mV时的幅度，消除了起搏电流的反转，使起搏电流的激活范围向更负的电位移动，并降低了起搏电流动力学的电压依赖性。加入Rb+到-90 mV时，对起搏电流的大小或时间进程几乎没有影响，但使起搏电流的反转向更负的方向移动。现有证据表明，Ba2+-Tyrode溶液中的起搏电流为超极化激活的内向电流。然而，Ba2+以剂量依赖的、可能的电压依赖的方式阻断起搏电流的未知部分。此外，起搏器衰退的缓慢成分的存在表明，用于分析起搏器电流的标准霍奇金-赫胥黎形式主义是不合适的。
The actions of Ba2+ and Rb+, two blockers of background K+ conductance, were investigated. Recent studies performed on ungulate Purkinje fibres have suggested that the pace‐maker current is an inward current activated by hyperpolarization. This hypothesis is based on the assumption that Ba2+ reduces the inwardly rectifying background K+ conductance without affecting the pace‐maker current. Addition of 5 mM‐BaCl2 to the bathing Tyrode solution decreases background K+ permeability and eliminates the reversal of the pace‐maker current. The reversal reappears on return to Ba2+‐free Tyrode solution. 5 mM‐BaCl2 also reduces the time‐dependent current at pace‐maker potentials positive to about ‐95 mV in 4 mM‐K+ Tyrode solution. The pace‐maker current in Ba2+ Tyrode solution usually does not have an exponential time course, and often decays non‐monotonically. It can take more than two minutes to reach a steady state. The fast initial component of membrane current, which is observed on hyperpolarizing in the pace‐maker potential range in Purkinje fibres and which has been called the ‘depletion current', is still present in Ba2+ Tyrode solution, but is reduced or eliminated if 10 mM‐CsCl is added to the Ba2+ Tyrode solution. The addition of Cs+ is accompanied by an outward shift in membrane current in Ba2+ Tyrode solution. Ba2+ reduces the background K+ permeability in a dose‐dependent manner. Addition of between 0.5 and 1 mM‐BaCl2 achieves a maximum effect. Raising the amount of BaCl2 above this level reduces the time‐dependent current even when no further effect on background permeability is observed. Rb+ substitution for K+ reduces the magnitude of the pace‐maker current at potentials positive to ‐100 mV, eliminates the reversal of the pace‐maker current, shifts the activation range to more negative potentials, and decreases the voltage dependence of pace‐maker current kinetics. Rb+ addition to Tyrode solution has little effect on pace‐maker current magnitude or time course positive to ‐90 mV, but does shift the reversal to more negative potentials. The available evidence suggests that the pace‐maker current in Ba2+ Tyrode solution is an inward current activated by hyperpolarization. However, Ba2+ blocks an unknown fraction of the pace‐maker current in a dose‐dependent, and possibly voltage‐dependent manner. Also, the presence of a slow component of pace‐maker decay suggests that the standard Hodgkin‐Huxley formalism for the analysis of pace‐maker currents is inappropriate.