Lee Urvi S, Cui Jianmin
Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, MO 63130, USA.
J Physiol. 2009 Apr 1;587(Pt 7):1481-98. doi: 10.1113/jphysiol.2009.169243. Epub 2009 Feb 9.
Large conductance Ca(2+)-activated K(+) (BK) channels modulate many physiological processes including neuronal excitability, synaptic transmission and regulation of myogenic tone. A gain-of-function (E/D) mutation in the pore-forming alpha subunit (Slo1) of the BK channel was recently identified and is linked to human neurological diseases of coexistent generalized epilepsy and paroxysmal dyskinesia. Here we performed macroscopic current recordings to examine the effects of the E/D mutation on the gating kinetics, and voltage and Ca(2+) dependence of the BK channel activation in the presence of four different beta subunits (beta1-4). These beta subunits are expressed in a tissue-specific pattern and modulate BK channel function differently, providing diversity and specificity for BK channels in various physiological processes. Our results show that in human (h) Slo1-only channels, the E/D mutation increased the rate of opening and decreased the rate of closing, allowing a greater number of channels to open at more negative potentials both in the presence and absence of Ca(2+) due to increased Ca(2+) affinity and enhanced activation compared with the wild-type channels. Even in the presence of beta subunits, the E/D mutation exhibited these changes with the exception of beta3b, where Ca(2+) sensitivity changed little. However, quantitative examination of these changes shows the diversity of each beta subunit and the differential modulation of these subunits by the E/D mutation. For example, in the presence of the beta1 subunit the E/D mutation increased Ca(2+) sensitivity less but enhanced channel activation in the absence of Ca(2+) more than in hSlo1-only channels, while in the presence of the beta2 subunit the E/D mutation also altered inactivation properties. These findings suggest that depending on the distribution of the various beta subunits in the brain, the E/D mutation can modulate BK channels differently to contribute to the pathophysiology of epilepsy and dyskinesia. Additionally, these results also have implications on physiological processes in tissues other than the brain where BK channels play an important role.
大电导钙激活钾（BK）通道调节许多生理过程，包括神经元兴奋性、突触传递和肌源性张力调节。最近在BK通道的孔形成α亚基（Slo1）中发现了一种功能获得性（E/D）突变，该突变与共存的全身性癫痫和发作性运动障碍的人类神经疾病有关。在这里，我们进行了宏观电流记录，以研究E/D突变对门控动力学以及在四种不同β亚基（β1-4）存在下BK通道激活的电压和钙依赖性的影响。这些β亚基以组织特异性模式表达，并以不同方式调节BK通道功能，为BK通道在各种生理过程中提供多样性和特异性。我们的结果表明，在仅含人（h）Slo1的通道中，E/D突变增加了开放速率并降低了关闭速率，与野生型通道相比，由于钙亲和力增加和激活增强，在有和没有钙的情况下，更多数量的通道在更负的电位下开放。即使在存在β亚基的情况下，除了β3b外，E/D突变也表现出这些变化，其中钙敏感性变化很小。然而，对这些变化的定量检查显示了每个β亚基的多样性以及E/D突变对这些亚基的差异调节。例如，在存在β1亚基的情况下,E/D突变增加钙敏感性的程度较小，但在没有钙的情况下比仅含hSlo1的通道更能增强通道激活，而在存在β2亚基的情况下，E/D突变也改变了失活特性。这些发现表明，根据大脑中各种β亚基的分布，E/D突变可以对BK通道进行不同的调节，从而导致癫痫和运动障碍的病理生理过程。此外，这些结果也对大脑以外的其他组织中的生理过程有影响，在这些组织中BK通道起着重要作用。
