Adams C M, Price M P, Snyder P M, Welsh M J
Howard Hughes Medical Institute and Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242 USA.
Biophys J. 1999 Mar;76(3):1377-83. doi: 10.1016/S0006-3495(99)77299-1.
The brain Na+ channel-1 (BNC1, also known as MDEG1 or ASIC2) is a member of the DEG/ENaC cation channel family. Mutation of a specific residue (Gly430) that lies N-terminal to the second membrane-spanning domain activates BNC1 and converts it from a Na+-selective channel to one permeable to both Na+ and K+. Because all K+ channels are blocked by tetraethylammonium (TEA), we asked if TEA would inhibit BNC1 with a mutation at residue 430. External TEA blocked BNC1 when residue 430 was a Val or a Thr. Block was steeply voltage-dependent and was reduced when current was outward, suggesting multi-ion block within the channel pore. Block was dependent on the size of the quaternary ammonium; the smaller tetramethylammonium blocked with similar properties, whereas the larger tetrapropylammonium had little effect. When residue 430 was Phe, the effects of tetramethylammonium and tetrapropylammonium were not altered. In contrast, block by TEA was much less voltage-dependent, suggesting that the Phe mutation introduced a new TEA binding site located approximately 30% of the way across the electric field. These results provide insight into the structure and function of BNC1 and suggest that TEA may be a useful tool to probe function of this channel family.
脑钠离子通道1（BNC1，也称为MDEG1或ASIC2）是DEG/ENaC阳离子通道家族的成员。位于第二个跨膜结构域N端的一个特定残基（Gly430）发生突变会激活BNC1，并使其从一个钠离子选择性通道转变为一个对钠离子和钾离子都通透的通道。由于所有钾离子通道都被四乙铵（TEA）阻断，我们探究了TEA是否会抑制残基430发生突变的BNC1。当残基430为缬氨酸或苏氨酸时，胞外TEA会阻断BNC1。阻断作用强烈依赖电压，且当电流外向时阻断作用减弱，这表明通道孔内存在多离子阻断。阻断作用取决于季铵盐的大小；较小的四甲铵以类似的特性进行阻断，而较大的四丙铵几乎没有作用。当残基430为苯丙氨酸时，四甲铵和四丙铵的作用没有改变。相比之下，TEA的阻断作用对电压的依赖性要小得多，这表明苯丙氨酸突变引入了一个新的TEA结合位点，该位点位于电场约30%的位置。这些结果为深入了解BNC1的结构和功能提供了线索，并表明TEA可能是探究该通道家族功能的有用工具。
