Bevans C G, Kordel M, Rhee S K, Harris A L
Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Biol Chem. 1998 Jan 30;273(5):2808-16. doi: 10.1074/jbc.273.5.2808.
Intercellular connexin channels (gap junction channels) have long been thought to mediate molecular signaling between cells, but the nature of the signaling has been unclear. This study shows that connexin channels from native tissue have selective permeabilities, partially based on pore diameter, that discriminate among cytoplasmic second messenger molecules. Permeability was assessed by measurement of selective loss/retention of tracers from liposomes containing reconstituted connexin channels. The tracers employed were tritiated cyclic nucleotides and a series of oligomaltosaccharides derivatized with a small uncharged fluorescent moiety. The data define different size cut-off limits for permeability through homomeric connexin-32 channels and through heteromeric connexin-32/connexin-26 channels. Connexin-26 contributes to a narrowed pore. Both cAMP and cGMP were permeable through the homomeric connexin-32 channels. cAMP was permeable through only a fraction of the heteromeric channels. Surprisingly, cGMP was permeable through a substantially greater fraction of the heteromeric channels than was cAMP. The data suggest that isoform stoichiometry and/or arrangement within a connexin channel determines whether cyclic nucleotides can permeate, and which ones. This is the first evidence for connexin-specific selectivity among biological signaling molecules.
长期以来，人们一直认为细胞间连接蛋白通道（间隙连接通道）介导细胞间的分子信号传导，但信号传导的本质尚不清楚。这项研究表明，来自天然组织的连接蛋白通道具有选择性通透性，部分基于孔径，能够区分细胞质中的第二信使分子。通过测量含有重组连接蛋白通道的脂质体中示踪剂的选择性损失/保留来评估通透性。所使用的示踪剂是氚标记的环核苷酸和一系列用小的不带电荷的荧光部分衍生化的低聚麦芽糖。数据确定了通过同型连接蛋白32通道和异型连接蛋白32/连接蛋白26通道的通透性的不同大小截止极限。连接蛋白26导致孔径变窄。cAMP和cGMP都可通过同型连接蛋白32通道。cAMP仅可通过一部分异型通道。令人惊讶的是，cGMP可通过的异型通道比例远大于cAMP。数据表明，连接蛋白通道内的异构体化学计量和/或排列决定了环核苷酸是否能够通透以及哪些环核苷酸能够通透。这是生物信号分子之间连接蛋白特异性选择性的首个证据。
