菠菜叶片类囊体膜上K^+通道的直接测定及其离子选择性

DIRECT MEASUREMENT OF THE K^+ CHANNEL AND ITS ION SELECTIVITY IN THE THYLAKOID MEMBRANE FROM SPINACH (SPINACEA OLERACEA L.) LEAVES

将经蔗糖密度梯度离心纯化的菠菜（Ｓｐｉｎａｃｅａ ｏｌｅｒａｃｅａ Ｌ．） 叶片类囊体膜微囊泡嵌入平面脂双层（ｐｌａｎａｒ ｌｉｐｉｄ ｂｉｌａｙｅｒｓ），至少检测到一种Ｋ＋ 单通道信号， 其电导约为５５ ｐＳ，具有电压依赖特性，对ＴＥＡ（ｔｅｔｒａｅｔｈｙｌａｍ ｍ ｏｎｉｕｍ ｃｈｌｏｒｉｄｅ）敏感，这一通道的ＰＫ＋ ／ＰＣｌ－ 通透比约为１４．９。离子通道的选择性可以在对称的离子条件下测定不同离子的电导，或者在双离子条件下测定反转电位确定，其对单价阳离子的选择顺序为：Ｋ＋ ＞ Ｎａ＋ ＞ Ｌｉ＋ ＞ ＮＨ＋４ ＞ Ｃｓ＋ 。

Thylakoid vesicles were purified from spinach(Spinacea oleracea L.) leaves by sucrose density gradient centrifugation and incorporated into planar lipid bilayers by stirring. At least one type of voltage dependent K + single channel currents was found. Its conductance(between +60 mV and -60 mV ) was about 55 pS in symmetrical (cis∶trans) 250 mmol/L KCl.This channel was sensitive to TEA (tetraethylammonium chloride) and the permeability ratio(P K + /P Cl - ) was about 14.9. The selectivity of 55 pS channel determined from both reversal potentials under bi ionic conditions or from conductance measurements in symmetrical solutions, was in the seguence of K + >Na +>Li +>NH + 4 > Cs + . This potassium channel could act as involved in charge balancing during light driven proton uptake by thylakoid.