Analysis of inhibitory mechanisms on Ca^<2+>-dependent K^+ channel influenced by exposure to a time-varying strong magnetic field.

我们测试了暴露于以下两种磁场（MF）对培养细胞的影响。(a)时变MF在0.07和1.7 T之间以3秒的间隔变化。(b)极低频（ELF）ME（800高斯，50 Hz）。(1)ME（a）对HeLa细胞的作用：用高K^+培养液代替正常培养液，可激活HeLa细胞K^+摄取，增加细胞内Ca^2+浓度。研究发现，一种具有膜渗透性的Ca^2+螯合剂和Ca^2+依赖性K^+通道抑制剂可以降低K^+的摄取。在高K^+培养基中，暴露于MF可部分抑制药物敏感性K^+摄取，并完全抑制细胞内Ca^<2+>的增加。但加入Ca^<2+>离子载体不能恢复MF对K^+吸收的抑制作用。K^+通量的抑制可能与细胞表面电性质的改变以及Ca^2+内流或Ca^2+从细胞Ca^2+库释放的抑制有关。(2)FT-IR光谱分析ELF MF（B）对HeLa细胞的作用：在1500-1700 cm ~（-1）区的光谱分析中<-1>，MF使酰胺Ⅱ模式（1540 cm ~（-1））的吸光度降低，使1600 cm ~（-1）附近的吸收<-1>带瞬间增加，后者吸光度的增加表明游离羧基的C=O对称振动增加。这一结果表明，细胞膜的蛋白质结构和细胞表面的电特性的变化。(3)ELF MF（a）对牛肾上腺嗜铬细胞的影响：我们检测了暴露于随时间变化的MF（a）对由缓激肽刺激的嗜铬细胞内Ca^&lt;2+&gt;瞬时升高的影响。加入缓激肽可在几分钟内引起细胞内Ca^&lt;2+&gt;的增加，而在无Ca^&lt;2 +&gt;的培养基中，MF可完全抑制细胞内Ca^&lt;2 +&gt;的增加。当最大磁场强度大于1.4 T时，抑制作用持续15 min，表明磁场对细胞囊泡Ca^2+释放有抑制作用。

We tested the effects of exposure to following two magnetic fields (MF) on cultured cells.(a) A time-varying MF changing between 0.07 and 1.7 T at an interval of 3 sec.(b) Extremely-low-frequency (ELF) ME (800 gauss, 50 Hz).(1) Effects of ME (a) on HeLa cells :K^+ uptake was activated and the intracellular Ca^<2+> concentration was increased by replacement of normal medium to high K^+ medium. A membrane-permeable Ca^<2+> chelating agent and Ca^<2+>-dependent K^+ channel inhibitors were found to reduce the K^+ uptake. Exposure to the MF partly inhibited the drug-sensitive K^+ uptake and completely suppressed the increase in intracellular Ca^<2+> in the high K^+ medium. But the inhibition of K^+ uptake by the MF was not restored by addition of Ca^<2+> ionophore. The suppression of K^+ fluxes could relate to a change in electric properties of cell surface and an inhibition of Ca^<2+> influx or Ca^<2+> release from cellular Ca^<2+> stores.(2) Analysis of ELF MF(b) effects on HeLa cells by FT-IR spectra :In analysis of the spectra of the 1500-1700 cm^<-1> region, absorbance of amide II mode (1540 cm-1)was decreased and a band about 1600 cm^<-1> was increased instantly by the MF.Increase in absorbance of the latter band reveals the increase on C=O symmetric vibration of free carboxyl. This results suggest changes in the protein structure of cell membrane and electric properties of cell surface.(3) Effects of ELF MF(a) on bovine adrenal chromaffin cells :We tested the effects of exposure to the time-varying MF(a) on transient increase in intracellular Ca^<2+> stimulated by bradykinin in chromaffin cells. Addition of bradykinin induced the increase in intracellular Ca^<2+> within few minutes.The exposure to the MF perfectly suppressed thc increase in cellular Ca^<2+> in Ca^<2+>-free medium. The inhibition occurred for 15 rain when the maximum magnetic flux density was more than 1.4 T.These results suggest that the exposure inhibits Ca^<2+> release from cellular vesicles.