Caffeine-activated large-conductance plasma membrane cation channels in cardiac myocytes: characteristics and significance.
Caffeine-activated large-conductance plasma membrane cation channels in cardiac myocytes: characteristics and significance.
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咖啡因激活心肌细胞大电导质膜阳离子通道：特征和意义。
DOI：
10.1152/ajpheart.00032.2007
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Zou,Hui
中科院分区：
文献类型：
--
作者：
Zhang,Yu-An;Tuft,RichardA;Lifshitz,LawrenceM;Fogarty,KevinE;Singer,JoshuaJ;Zou,Hui
咖啡因激活的，大电导，非选择性阳离子通道（LCC）已被发现在分离的心肌细胞的质膜在几个物种。然而，人们对开放这些渠道的影响知之甚少。为了研究这种效应并进一步了解咖啡因激活机制，我们使用全细胞膜片钳技术对大鼠和小鼠新鲜分离的心肌细胞进行了研究。与以前的研究不同，使用毒胡萝卜素，使得打开LCC的效果和咖啡因的作用都不依赖于细胞内储存的Ca 2+释放。这些Ca 2 +-可渗透的LCC被发现在大多数的细胞从心房和心室，在大鼠心房的电导为10370 pS。咖啡因及其直接代谢产物（茶碱、可可碱和副黄嘌呤）激活了该通道，而异咖啡因则没有。虽然它们与兰尼碱受体（RyR，其开口引起Ca 2+火花）有一些相似之处，但LCC也显示出一些不同的特征。与同时的Ca 2+成像和电流记录，局部荧光增加由于Ca 2+进入通过一个单一的开口的LCC（SCCaFT）被检测到。当记录膜电位而不是电流时，发现SCCaFT样荧光瞬变（指示单个LCC开口）伴随膜去极化。据我们所知，这是第一份直接将膜电位变化与离子通道的单一开放联系起来的报告。此外，心肌细胞中的这些事件表明咖啡因和茶碱有助于产生心律失常的可能的额外机制。
Caffeine-activated, large-conductance, nonselective cation channels (LCCs) have been found in the plasma membrane of isolated cardiac myocytes in several species. However, little is known about the effects of opening these channels. To examine such effects and to further understand the caffeine-activation mechanism, we carried out studies using whole-cell patch-clamp techniques with freshly isolated cardiac myocytes from rats and mice. Unlike previous studies, thapsigargin was used so that both the effect of opening LCCs and the action of caffeine were independent of Ca2+release from intracellular stores. These Ca2+-permeable LCCs were found in a majority of the cells from atria and ventricles, with a conductance of ∼370 pS in rat atria. Caffeine and all its direct metabolic products (theophylline, theobromine, and paraxanthine) activated the channel, while isocaffeine did not. Although they share some similarities with ryanodine receptors (RyRs, the openings of which give rise to Ca2+sparks), LCCs also showed some different characteristics. With simultaneous Ca2+imaging and current recording, the localized fluorescence increase due to Ca2+entry through a single opening of an LCC (SCCaFT) was detected. When membrane potential, instead of current, was recorded, SCCaFT-like fluorescence transients (indicating single LCC openings) were found to accompany membrane depolarizations. To our knowledge, this is the first report directly linking membrane potential changes to a single opening of an ion channel. Moreover, these events in cardiac cells suggest a possible additional mechanism by which caffeine and theophylline contribute to the generation of cardiac arrhythmias.