Guo W, Kamiya K, Hojo M, Kodama I, Toyama J
Department of Circulation, Nagoya University, Chikusa-ku, Japan.
J Mol Cell Cardiol. 1998 Jul;30(7):1449-55. doi: 10.1006/jmcc.1998.0730.
Postnatal development and myocardial hypertrophy are associated with alterations in cardiac voltage-gated K+ channels. To investigate mechanisms underlying this K+ channel remodeling, expression of Kv4.2 and Kv1.4 K+ channel alpha-subunits was examined in cultured newborn rat ventricular myocytes by Western blot analysis using polyclonal antibodies against each of the subunits. At day 5 of cell culture, Kv1.4 protein was expressed at higher level than Kv4.2; as the age of culture progressed, Kv1.4 was significantly diminished while Kv4.2 increased with time in culture and became the predominant K+ channel protein. Such K+ channel isoform switch from Kv1.4 to Kv4.2 resembles that of the development in vivo. A 72-h treatment with exogenous triiodothyronine (T3, 0.1 microM) to cultured neonatal myocytes enhanced the expression of Kv4.2 by 73% and decreased the Kv1.4 expression by 22%. The effects of T3 were associated with an increase in the protein-to-DNA ratio indicating myocyte hypertrophy. On the other hand, a 72-h treatment with cardiac non-myocyte cell (NMC)-conditioned growth medium (NCGM) or phenylephrine (20 microM) induced similar cell hypertrophy, but in sharp contrast to T3, both markedly suppressed the Kv4.2 channel protein level. In addition, the trophic and the Kv4.2-downregulating effects of NCGM could be mimicked by exogenous endothelin-1 (0.1 microM), a paracrine factor secreted from cardiac NMCs. Our observations for the first time suggest that cardiac Kv4.2 and Kv1.4 K+ channel alpha-subunits are differentially regulated by a variety of myocardial hypertrophic factors. That T3 accelerated the developmental K+ channel isoform switch from Kv1.4 to Kv4.2 in vitro indicates the critical importance of thyroid hormone in postnatal K+ channel remodeling. Cardiac NMCs and alpha-adrenoceptor activation may contribute to the reduced outward K+ channel density in hypertrophied cardiomyocytes.
出生后发育和心肌肥大与心脏电压门控钾通道的改变有关。为了研究这种钾通道重塑的潜在机制，通过使用针对每个亚基的多克隆抗体进行蛋白质印迹分析，检测了培养的新生大鼠心室肌细胞中Kv4.2和Kv1.4钾通道α亚基的表达。在细胞培养的第5天，Kv1.4蛋白的表达水平高于Kv4.2；随着培养时间的延长，Kv1.4显著减少，而Kv4.2随培养时间增加并成为主要的钾通道蛋白。这种从Kv1.4到Kv4.2的钾通道亚型转换类似于体内的发育情况。用外源性三碘甲状腺原氨酸（T3，0.1微摩尔）对培养的新生心肌细胞进行72小时处理，可使Kv4.2的表达增加73%，并使Kv1.4的表达降低22%。T3的作用与蛋白质与DNA比值的增加有关，表明心肌细胞肥大。另一方面，用心脏非心肌细胞（NMC）条件培养基（NCGM）或去氧肾上腺素（20微摩尔）进行72小时处理可诱导类似的细胞肥大，但与T3形成鲜明对比的是，两者均显著抑制Kv4.2通道蛋白水平。此外，外源性内皮素-1（0.1微摩尔）可模拟NCGM的营养作用和下调Kv4.2的作用，内皮素-1是心脏NMC分泌的一种旁分泌因子。我们的观察首次表明，心脏Kv4.2和Kv1.4钾通道α亚基受到多种心肌肥大因子的差异调节。T3在体外加速了从Kv1.4到Kv4.2的发育性钾通道亚型转换，这表明甲状腺激素在出生后钾通道重塑中至关重要。心脏NMC和α肾上腺素能受体激活可能导致肥大心肌细胞外向钾通道密度降低。
