Bellemare F, Dubé L, Sauvé R
Département de physiologie, Faculté de médicine, Université de Montréal, QC, Canada.
Can J Physiol Pharmacol. 1996 Mar;74(3):265-72.
The presence of nonselective ionic channels at the apical membrane of rabbit proximal tubule cells was investigated by fusion of proximal tubule brush border membrane vesicles onto a planar bilayer and by means of patch clamp measurements on primary cultured proximal tubule cells. The fusion of brush border membrane vesicles onto a phosphatidylethanolamine-phosphatidylcholine (1:1) planar bilayer led to the identification of a nonselective channel of 115 pS in 200 mM NaCl conditions with an ionic permeability sequence for Na+, K+, and Cl- corresponding to PNa/PK = 0.3 and PNa/PCl = 3, respectively. This channel showed an increased open probability at depolarizing potentials, but its activity was independent of the Ca2+ concentration in both the cis and trans compartments. These findings were subsequently confirmed in inside-out patch clamp experiments carried out on primary cultured proximal tubule cells. This channel was seldom seen in cell-attached recordings on resting cells, but its presence was observed with a higher probability in patch excised experiments performed following superfusion of the cells with a hypotonic solution. It is suggested on the basis of these observations that the apical membrane of rabbit proximal tubule cells contains a voltage-dependent nonselective channel, the activity of which may contribute to the regulation of the membrane potential.
通过将近端小管刷状缘膜囊泡融合到平面双层膜上，并对原代培养的近端小管细胞进行膜片钳测量，研究了兔近端小管细胞顶端膜上非选择性离子通道的存在情况。刷状缘膜囊泡与磷脂酰乙醇胺 - 磷脂酰胆碱（1:1）平面双层膜的融合，使得在200 mM NaCl条件下鉴定出一个115 pS的非选择性通道，其对Na⁺、K⁺和Cl⁻的离子通透序列分别对应PNa/PK = 0.3和PNa/PCl = 3。该通道在去极化电位下开放概率增加，但其活性在顺式和反式隔室中均与Ca²⁺浓度无关。这些发现随后在对原代培养的近端小管细胞进行的内向外膜片钳实验中得到证实。在静息细胞的细胞贴附记录中很少见到该通道，但在用低渗溶液对细胞进行灌流后进行的膜片切除实验中，观察到其存在的概率更高。基于这些观察结果，提示兔近端小管细胞的顶端膜含有一种电压依赖性非选择性通道，其活性可能有助于调节膜电位。
