Comtois A, Light P, Renaud J M, Kong M
University of Ottawa, Department of Physiology, Ontario, Canada.
Eur J Pharmacol. 1993 Sep 21;242(1):65-73. doi: 10.1016/0014-2999(93)90011-6.
The goal of this study was to characterize the effects of tolbutamide and glyburide, two known KATP channel blockers, on intact, unfatigued sartorius muscle fibres of the frog, Rana pipiens. Tetanic contractions were elicited by field stimulation with 200 ms long train of pulses (0.5 ms, 6 V, 140 Hz). Resting and action potentials were measured using conventional microelectrodes. At pHo 7.2 (extracellular pH), the tetanic force was unaffected by 0.5 mM and 1.0 mM tolbutamide, but at 2.0 mM it decreased by 15.5 +/- 1.0%. The effect of tolbutamide on the tetanic force was significantly greater at pHo 6.4: all three tolbutamide concentrations caused a significant decrease in tetanic force, being 62.3 +/- 9.4% at 2 mM. In the presence of tolbutamide a large number of fibres became unexcitable at pHo 6.4, but not at pHo 7.2. Glyburide at 10 microM, on the other hand, caused a 5-7% decrease in tetanic force at both pHo 6.4 and 7.2, but no further decreases in tetanic force were observed when the glyburide concentration was increased up to 100 microM. Unlike tolbutamide, glyburide did not affect the excitability of muscle fibres, but significantly prolonged the repolarization phase of action potentials, especially at pHo 6.4. We suggest that several of the tolbutamide effects reported in this study cannot be accounted for by a direct effect on KATP channels, and that the large decrease in membrane excitability and muscle contractility in the presence of tolbutamide must seriously be taken into consideration when this channel blocker is used to study the physiological role of KATP channels in intact muscle fibres.
本研究的目的是表征两种已知的ATP敏感性钾通道（KATP通道）阻滞剂甲苯磺丁脲和格列本脲对完整、未疲劳的牛蛙（Rana pipiens）缝匠肌纤维的影响。通过施加200 ms长的脉冲串（0.5 ms，6 V，140 Hz）进行场刺激来引发强直收缩。使用传统微电极测量静息电位和动作电位。在细胞外pH值（pHo）为7.2时，0.5 mM和1.0 mM的甲苯磺丁脲对强直力没有影响，但在2.0 mM时，强直力下降了15.5±1.0%。在pHo为6.4时，甲苯磺丁脲对强直力的影响显著更大：所有三种甲苯磺丁脲浓度均导致强直力显著下降，在2 mM时为62.3±9.4%。在甲苯磺丁脲存在的情况下，大量纤维在pHo为6.4时变得不可兴奋，但在pHo为7.2时并非如此。另一方面，10 μM的格列本脲在pHo为6.4和7.2时均导致强直力下降5 - 7%，但当格列本脲浓度增加至100 μM时，未观察到强直力进一步下降。与甲苯磺丁脲不同，格列本脲不影响肌肉纤维的兴奋性，但显著延长了动作电位的复极化阶段，尤其是在pHo为6.4时。我们认为，本研究中报道的甲苯磺丁脲的几种作用不能通过对KATP通道的直接作用来解释，并且在使用这种通道阻滞剂研究完整肌肉纤维中KATP通道的生理作用时，必须认真考虑甲苯磺丁脲存在时膜兴奋性和肌肉收缩性的大幅下降。
