Fink R, Hase S, Lüttgau H C, Wettwer E
J Physiol. 1983 Mar;336:211-28. doi: 10.1113/jphysiol.1983.sp014577.
The increase in K+ conductance induced by repetitive stimulation in metabolically poisoned sartorius muscle fibres of the frog was investigated, using a two-micro-electrode voltage-clamp technique. After the inhibition of creatine kinase by 0.4 mM-1-fluoro-2,4-dinitrobenzene (FDNB) and a complete and irreversible exhaustion of contractility, a nearly linear current-voltage relation was measured between -100 and 0 mV. In the presence of CN- (4 mM) an 'intermediate state' could be established by repetitive stimulation towards complete mechanical exhaustion. In this labile state, the high and potential-independent K+ conductance could be induced by repetitive voltage-clamp pulses (100 ms duration) from -85 to 0 mV membrane potential. After the pulses had ceased, fibres regained their original membrane conductance within several minutes. After the electrophoretic injection of the Ca2+-chelating agent H2EGTA2- into fibres in the intermediate state, an increase in membrane conductance by repetitive voltage-clamp pulses could no longer be induced. Fibres in the intermediate state into which H2EGTA2- -buffered Ca2+ (free Ca2+ approximately 10(-5) M) was injected, or to which external caffeine (1.5 mM) was applied, showed a spontaneous and reversible increase in membrane conductance. In metabolically poisoned and mechanically exhausted sartorius muscles the concentrations of creatine phosphate (CP) and ATP were estimated using biochemical standard methods. The concentration of CP remained basically unchanged after FDNB poisoning. In solutions containing CN- plus iodoacetate CP fell below the detectable concentration of about 0.5-1% of the normal value. ATP decreased to slightly less than 20% under both conditions. It is concluded that internal free Ca2+ promotes the activation of the K+ conductance in exhausted muscle fibres, and that a shortage of energy reserves increases the 'sensitivity' of K+ channels to Ca2+ ions.
采用双微电极电压钳技术，研究了蛙缝匠肌纤维在代谢中毒情况下重复刺激所诱导的钾离子电导增加。在用0.4 mM的1-氟-2,4-二硝基苯（FDNB）抑制肌酸激酶且收缩力完全不可逆耗尽后，在-100至0 mV之间测量到了近乎线性的电流-电压关系。在存在4 mM氰化物（CN-）的情况下，通过向完全机械性疲劳方向重复刺激可建立一种“中间状态”。在这种不稳定状态下，从-85至0 mV膜电位的重复电压钳脉冲（持续时间100 ms）可诱导出高且与电位无关的钾离子电导。脉冲停止后，纤维在几分钟内恢复其原来的膜电导。向处于中间状态的纤维中电泳注入钙离子螯合剂乙二醇双（2-氨基乙醚）四乙酸（H2EGTA2-）后，重复电压钳脉冲不再能诱导膜电导增加。向处于中间状态的纤维中注入H2EGTA2-缓冲的钙离子（游离钙离子约10^(-5) M）或施加外部咖啡因（1.5 mM）后，纤维的膜电导出现自发且可逆的增加。使用生化标准方法估计了代谢中毒且机械性疲劳的缝匠肌中磷酸肌酸（CP）和三磷酸腺苷（ATP）的浓度。FDNB中毒后CP浓度基本保持不变。在含有CN-加碘乙酸盐的溶液中，CP降至低于约为正常值0.5 - 1%的可检测浓度。在两种情况下，ATP均降至略低于20%。结论是，细胞内游离钙离子促进疲劳肌纤维中钾离子电导的激活，并且能量储备的短缺增加了钾离子通道对钙离子的“敏感性”。
