Gating of cx46 gap junction hemichannels by calcium and voltage
Gating of cx46 gap junction hemichannels by calcium and voltage
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DOI：
10.1007/s004240050788
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发表时间：
1999-02-01
影响因子：
4.5
通讯作者：
Dahl, G
中科院分区：
文献类型：
--
作者：
Pfahnl, A;Dahl, G
连接蛋白46（Connexin 46，cx46）在非洲爪蟾卵母细胞中表达后，不仅在成对细胞间形成典型的缝隙连接通道，而且在单个细胞的质膜上形成开放的缝隙连接半通道。差距连接半通道在渗透性和门控方面与完整间隙连接通道共享特性。在这里，我们的特点门，关闭半通道响应钙浓度增加与全细胞和单通道记录。通道在细胞外钙浓度（1-2 mM）的窄范围内关闭，所述浓度包括在cx 46表达的主要位点（透镜）中占优势的钙浓度。钙离子对通道的影响取决于电压。使用cx46的半胱氨酸突变体cx46 L35 C来确定门的定位。实验证据表明，位置35是孔衬里。定位方案测试位置35对于细胞外或细胞内应用于由钙封闭的通道的硫醇试剂的可及性。钙离子通道关闭将硫醇试剂从外部排除，但不从内部排除。因此，门导致孔的区域性关闭，并且其位于cx46的位置35的细胞外。目前的数据还表明，cx46缝隙连接半通道可能发挥生理功能的透镜。考虑到钙与白内障形成的关系，cx46缝隙连接半通道的失调可能是白内障的原因之一。
Connexin 46 (cx46), when expressed in Xenopus oocytes, not only forms typical gap junction channels between paired cells but also forms open gap junction hemichannels in the plasma membrane of single cells. The gap junction hemichannels share properties with complete gap junction channels in terms of permeability and gating. Here we characterize the gate that closes hemichannels in response to increased calcium concentration with whole-cell and single-channel records. The channels close within a narrow range of extracellular calcium concentrations (1-2 mM) which includes the calcium concentration prevailing in the primary site of cx46 expression, the lens. The effect of calcium on the channels is determined by voltage. A cysteine mutant of cx46, cx46L35C, was used to determine the localization of the gate. Experimental evidence suggests that position 35 is pore lining. The localization protocol tests the accessibility of position 35 for thiol reagents applied extra- or intracellularly to the channel closed by calcium. Channel closure by calcium excluded the thiol reagent from the outside but not from the inside. Consequently, the gate results in a regional closure of the pore and it is located extracellular to the position 35 of cx46. The present data also suggest that the cx46 gap junction hemichannel may exert a physiological function in the lens. Considering the association of calcium with cataract formation, it is feasible that misregulation of cx46 gap junction hemichannels could be a cause for cataract.