Brenner R, Jegla T J, Wickenden A, Liu Y, Aldrich R W
Howard Hughes Medical Institute, Molecular and Cellular Physiology, Stanford School of Medicine, Stanford, California 94305, USA.
J Biol Chem. 2000 Mar 3;275(9):6453-61. doi: 10.1074/jbc.275.9.6453.
We present the cloning and characterization of two novel calcium-activated potassium channel beta subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and brain, respectively. We compare and contrast the steady state and kinetic properties of these beta subunits with the previously cloned mouse beta1 (mKCNMB1) and the human beta2 subunit (hKCNMB2). Once inactivation is removed, we find that hKCNMB2 has properties similar to mKCNMB1. hKCNMB2 slows Hslo1 channel gating and shifts the current-voltage relationship to more negative potentials. hKCNMB3 and hKCNMB4 have distinct effects on slo currents not observed with mKCNMB1 and hKCNMB2. Although we found that hKCNMB3 does interact with Hslo channels, its effects on Hslo1 channel properties were slight, increasing Hslo1 activation rates. In contrast, hKCNMB4 slows Hslo1 gating kinetics, and modulates the apparent calcium sensitivity of Hslo1. We found that the different effects of the beta subunits on some Hslo1 channel properties are calcium-dependent. mKCNMB1 and hKCNMB2 slow activation at 1 microM but not at 10 microM free calcium concentrations. hKCNMB4 decreases Hslo1 channel openings at low calcium concentrations but increases channel openings at high calcium concentrations. These results suggest that beta subunits in diverse tissue types fine-tune slo channel properties to the needs of a particular cell.
我们展示了两个新的钙激活钾通道β亚基hKCNMB3和hKCNMB4的克隆及特性，它们分别在睾丸和大脑中富集。我们将这些β亚基的稳态和动力学特性与先前克隆的小鼠β1（mKCNMB1）和人类β2亚基（hKCNMB2）进行了比较和对比。一旦去除失活，我们发现hKCNMB2具有与mKCNMB1相似的特性。hKCNMB2减缓了Hslo1通道的门控，并将电流-电压关系向更负的电位移动。hKCNMB3和hKCNMB4对slo电流有独特的影响，而mKCNMB1和hKCNMB2未观察到这种影响。虽然我们发现hKCNMB3确实与Hslo通道相互作用，但其对Hslo1通道特性的影响很小，只是增加了Hslo1的激活速率。相比之下，hKCNMB4减缓了Hslo1的门控动力学，并调节了Hslo1的表观钙敏感性。我们发现β亚基对某些Hslo1通道特性的不同影响是钙依赖性的。mKCNMB1和hKCNMB2在游离钙浓度为1微摩尔时减缓激活，但在10微摩尔时则不然。hKCNMB4在低钙浓度下减少Hslo1通道的开放，但在高钙浓度下增加通道开放。这些结果表明，不同组织类型中的β亚基根据特定细胞的需求对slo通道特性进行微调。
