Functional and molecular evidence of MaxiK channel β1 subunit decrease with coronary artery ageing in the rat
Functional and molecular evidence of MaxiK channel β1 subunit decrease with coronary artery ageing in the rat
复制标题
DOI：
10.1113/jphysiol.2004.068676
复制
发表时间：
2004-09-15
影响因子：
5.5
通讯作者：
Toro, L
中科院分区：
文献类型：
--
作者：
Nishimaru, K;Eghbali, M;Toro, L
大电导、电压和钙离子激活的钾离子通道（MaxiK，BK）是血管张力的关键调节因子。血管中的MaxiK由形成孔道的α亚基和调节性的β1亚基组成，β1亚基赋予通道独特的动力学特性、钙离子/电压敏感性和药理学特性。随着年龄增长，冠状动脉心肌细胞中α亚基的功能表达和蛋白质水平降低。然而，衰老是否会改变β1亚基的表达以及α亚基减少的机制尚不清楚。因此，我们检测了年轻和年老的F344大鼠冠状动脉心肌细胞中MaxiK的功能和药理学特性，以及α和β1转录本水平。年龄依赖性的α亚基蛋白质减少的机制涉及到其转录本的下调。在老年心肌细胞中也检测到β1转录本的相应缺失，这表明β1与α亚基蛋白质呈年龄依赖性的成比例减少。实际上，由β1和α亚基共同组装所定义的MaxiK通道特性在年轻和年老的细胞中是相同的，例如在（i）激活动力学，（ii）对大于1μM的钙离子水平的敏感性，（iii）去氢大豆皂苷-I诱导的激活，以及（iv）伊贝毒素阻断方面。与老年心肌细胞中MaxiK表达/功能降低一致，随着年龄增长，伊贝毒素使冠状动脉环收缩的能力降低了约50%，这证实了我们之前的发现。在年轻的冠状动脉中，伊贝毒素预处理降低5 - 羟色胺（5 - HT）收缩效能的程度大于年老的冠状动脉（这是由于伊贝毒素在年轻冠状动脉中诱导的收缩更大，以及年轻与年老相比5 - HT收缩的动态范围减小），而硝酸甘油诱导的舒张没有明显差异。我们提出，与年龄相关的MaxiK减少涉及通过转录本下调机制使α和β1功能表达平行降低；对基础的以及可能受刺激的冠状动脉收缩的重大影响可能导致老年人冠状动脉血流调节改变和冠状动脉疾病的发生。
Large-conductance, voltage- and Ca2+-activated K+ channels (MaxiK, BK) are key regulators of vascular tone. Vascular MaxiK are formed by the pore-forming alpha subunit and the modulatory beta1 subunit, which imprints unique kinetics, Ca2+/voltage sensitivities and pharmacology to the channel. As age progresses, alpha subunit functional expression and protein levels diminish in coronary myocytes. However, whether ageing modifies beta1 subunit expression or the mechanism of alpha subunit reduction is unknown. Thus, we examined functional and pharmacological characteristics of MaxiK, as well as alpha and beta1 transcript levels in coronary myocytes from young and old F344 rats. The mechanism of age-dependent alpha subunit protein reduction involves its transcript downregulation. A corresponding loss of beta1 transcripts was also detected in old myocytes, suggesting a proportional age-dependent decrease of beta1 to alpha subunit protein. Indeed, MaxiK channel properties, defined by coassembly of beta1 and a subunits, were equivalent in young versus old, for example in terms of (i) activation kinetics, (ii) sensitivity to Ca2+ levels > 1 mum (iii) dehydrosoyasaponin-I-induced activation, and (iv) iberiotoxin blockade. Consistent with less MaxiK expression/function in older myocytes, the ability of iberiotoxin to contract coronary rings was reduced similar to50% with ageing confirming our previous findings. 5-Hydroxytryptamine (5-HT) contractile efficacy was reduced by iberiotoxin pretreatment in young > old coronary arteries (explained by larger iberiotoxin-induced contraction and decreased dynamic range for 5-HT contraction in young versus old) with no apparent differences in nitroglycerine-induced relaxation. We propose that the age-related MaxiK reduction involves a parallel decrease of alpha and beta1 functional expression via a transcript downregulatory mechanism; a major impact on basal and possibly stimulated coronary contraction may contribute to altered coronary flow regulation and coronary morbidity in the elderly.