不同离子对烟草根皮层细胞质膜内向K^＋通道的影响

Effects of Different Ions on the Inward K^+ -Channels in the Plasma Membrane of Protoplasts of Tobacco Root Cortex

以烟草(Nivotiana tobacum L.)为材料,利用膜片钳技术分析钙、钠、钾、锂4种离子对根皮层细胞质膜上内向钾通道的影响.结果表明,烟草根皮层细胞质膜上的内向钾通道对Na^+,Li^+敏感,并可被其抑制.且当胞外溶液中的K^+完全被Na^+和Li^+取代时,没有出现明显的内向电流.表明内向型钾通道对Na^+/K^+和Li^+/K^+具有极高的选择透性.当电压达到-170 mV时,同时增大胞外K^+浓度,由Ca^(2+)(7 mmol·L^(-1))处理的细胞质膜上内向钾通道的电流增加,而Mg^(2+)(25 mmol·L^(-1))处理的细胞质膜上内向钾通道的电流下降.暗示钙和镁虽属同族元素,且结构近似,但对烟草根皮层质膜上的内向钾通道在超级化作用下具有不同的作用机制.

In an attempt to understand the effect of Ca^2＋, Mg^2＋ , Na^＋ , Li^＋ on the electrical and physiological characteristic of inward K^＋-channels, the patch clamp whole-cell recording techniques were applied to protoplasts which were isolated from tobacco （Nicotiana tobacum L. ）root cortex. The results showed that the K^＋-channels in tobacco root cortex membrane were sensitive to either Na^＋ or Li^＋ , and could be partly inhibited by them. No obvious inward current was observed when the K^＋ in the bath solution was substituted for Li^＋. The K^＋ -channels were inhibited by external high concentrations of Ca^2＋ （7 mmol · L^-1） or Mg^2＋ （25 mmol · L^-1 ）. Butat - 170 mV, augmenting the external K^＋concentration at the same time, the experiments treated by Ca^2＋ or Mg^2＋ would present contrary phenomena. The currents treated by Ca^2＋ increased but another decreased. This demonstrated the mechanisms of Mg^2＋ and Ca^2＋ affecting K^＋ channel were different.