Alvarez Maubecin V, Sanchez V N, Rosato Siri M D, Cherksey B D, Sugimori M, Llinás R, Uchitel O D
Institute of Cellular Biology, School of Medicine, University of Buenos Aires, Argentina.
J Neurochem. 1995 Jun;64(6):2544-51. doi: 10.1046/j.1471-4159.1995.64062544.x.
The voltage-dependent calcium channels present in mammalian and chicken brain synaptosomes were characterized pharmacologically using specific blockers of L-type channels (1,4-dihydropyridines), N-type channels (omega-conotoxin GVIA), and P-type channels [funnel web toxin (FTX) and omega-agatoxin IVA]. K(+)-induced Ca2+ uptake by chicken synaptosomes was blocked by omega-conotoxin GVIA (IC50 = 250 nM). This toxin at 5 microM did not block Ca2+ entry into rat frontal cortex synaptosomes. FTX and omega-agatoxin IVA blocked Ca2+ uptake by rat synaptosomes (IC50 = 0.17 microliter/ml and 40 nM, respectively). Likewise, in chicken synaptosomes, FTX and omega-agatoxin IVA affected Ca2+ uptake, FTX (3 microliters/ml) exerted a maximal inhibition of 40% with an IC50 similar to the one obtained in rat preparations, whereas with omega-agatoxin IVA saturation was not reached even at 5 microM. In chicken preparations, the combined effect of saturating concentrations of FTX (1 microliter/ml) and different concentrations of omega-conotoxin GVIA showed no additive effects. However, the effect of saturating concentrations of FTX and omega-conotoxin GVIA was never greater than the one observed with omega-conotoxin GVIA. We also found that 60% of the Ca2+ uptake by rat and chicken synaptosomes was inhibited by omega-conotoxin MVIID (1 microM), a toxin that has a high index of discrimination against N-type channels. Conversely, nitrendipine (10 microM) had no significant effect on Ca2+ uptake in either the rat or the chicken. In conclusion, Ca2+ uptake by rat synaptosomes is potently inhibited by different P-type Ca2+ channel blockers, thus indicating that P-type channels are predominant in this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
利用L型通道特异性阻滞剂（1,4 - 二氢吡啶）、N型通道特异性阻滞剂（ω - 芋螺毒素GVIA）和P型通道特异性阻滞剂[漏斗网毒素（FTX）和ω - 阿加毒素IVA]，从药理学角度对存在于哺乳动物和鸡脑突触体中的电压依赖性钙通道进行了表征。ω - 芋螺毒素GVIA可阻断K⁺诱导的鸡突触体Ca²⁺摄取（IC50 = 250 nM）。该毒素在5 μM时并不阻断Ca²⁺进入大鼠额叶皮质突触体。FTX和ω - 阿加毒素IVA可阻断大鼠突触体的Ca²⁺摄取（IC50分别为0.17 μl/ml和40 nM）。同样，在鸡突触体中，FTX和ω - 阿加毒素IVA也影响Ca²⁺摄取，FTX（3 μl/ml）产生的最大抑制率为40%，其IC50与在大鼠制剂中获得的相似，而即使在5 μM时，ω - 阿加毒素IVA也未达到饱和。在鸡制剂中，饱和浓度的FTX（1 μl/ml）与不同浓度的ω - 芋螺毒素GVIA的联合作用未显示出相加效应。然而，饱和浓度的FTX和ω - 芋螺毒素GVIA的作用从未大于单独使用ω - 芋螺毒素GVIA时观察到的作用。我们还发现，ω - 芋螺毒素MVIID（1 μM）可抑制大鼠和鸡突触体60%的Ca²⁺摄取，该毒素对N型通道具有高度的区分指数。相反，尼群地平（10 μM）对大鼠或鸡的Ca²⁺摄取均无显著影响。总之，不同的P型钙通道阻滞剂可有效抑制大鼠突触体的Ca²⁺摄取，这表明P型通道在该制剂中占主导地位。（摘要截短至250字）
