Cho W J, Drescher M J, Hatfield J S, Bessert D A, Skoff R P, Drescher D G
Department of Otolaryngology, Wayne State University School of Medicine, Lande Medical Research Building, 540 East Canfield Avenue, Detroit, MI 48201, USA.
Neuroscience. 2003;118(2):525-34. doi: 10.1016/s0306-4522(02)00913-2.
The expression of transcript for hyperpolarization-activated, cyclic nucleotide-sensitive cation channel (HCN) isoforms underlying hyperpolarization-activated, inward current (I(h)) has been determined for a model hair-cell preparation from the saccule of the rainbow trout, Oncorhynchus mykiss. Based upon identification from homology to known vertebrate HCN cDNA sequence, cloning of PCR products amplified with degenerate primers indicated an expression frequency of 7:2:1 (HCN1:HCN2:HCN4) for the hair-cell sheet compared with 1:1:7 for brain. Full-length sequence has been obtained for the HCN1-like isoform representing the primary HCN transcript expressed in the hair-cell preparation. The channel protein is 938 amino acids in length with 93% amino acid identity for the region extending from the S1-S6 membrane spanning domains through the voltage-pore and cyclic nucleotide-binding domains, compared with HCN1 for rabbit, rat, mouse and human. The N- and C-terminal regions are less homologous, with 39-51% and 43-44% amino acid identities, respectively. Compared with other vertebrate HCN1, the hair-cell HCN1 contains additional consensus phosphorylation sites associated with unique repeats in the carboxy terminus. The HCN1-like transcript has been localized to hair cells of the saccular sensory epithelia by in situ hybridization. Previous electrophysiological studies have identified I(h) as the sole inwardly rectifying ion channel in a specific population of hair cells of the saccule of frogs [J Neurophysiol (1995) 73:1484] and fish [J Physiol (1996) 495:665]. I(h) is an important determinant of the resting membrane potential, and for this population of hair cells, is predicted to maintain the membrane potential within a voltage range allowing the voltage-gated calcium channels to open, permitting "spontaneous" release of transmitter. The molecular properties of the HCN1-like isoform underlying I(h) expressed in the saccular hair cells of the teleost, trout, may consequently impact spontaneous release of transmitter from hair cells of the saccule.
针对虹鳟（Oncorhynchus mykiss）球囊的一种模型毛细胞制备物，已经确定了超极化激活的内向电流（I(h)）背后的超极化激活的环核苷酸敏感阳离子通道（HCN）亚型转录本的表达情况。基于与已知脊椎动物HCN cDNA序列的同源性鉴定，用简并引物扩增的PCR产物的克隆表明，毛细胞片层中HCN的表达频率为7:2:1（HCN1:HCN2:HCN4），而脑内的表达频率为1:1:7。已经获得了代表毛细胞制备物中表达的主要HCN转录本的HCN1样亚型的全长序列。与兔、大鼠、小鼠和人类的HCN1相比，该通道蛋白长度为938个氨基酸，从S1 - S6跨膜结构域延伸穿过电压孔和环核苷酸结合结构域的区域具有93%的氨基酸同一性。N端和C端区域的同源性较低，氨基酸同一性分别为39 - 51%和43 - 44%。与其他脊椎动物的HCN1相比，毛细胞的HCN1在羧基末端含有与独特重复序列相关的额外共有磷酸化位点。通过原位杂交，已将HCN1样转录本定位到球囊感觉上皮的毛细胞中。先前的电生理研究已将I(h)鉴定为青蛙[《神经生理学杂志》（1995年）73:1484]和鱼类[《生理学杂志》（1996年）495:665]球囊特定毛细胞群体中唯一的内向整流离子通道。I(h)是静息膜电位的重要决定因素，对于该毛细胞群体，预计它能将膜电位维持在一个电压范围内，使电压门控钙通道开放，从而允许递质“自发”释放。因此，硬骨鱼虹鳟球囊毛细胞中表达的I(h)背后的HCN1样亚型的分子特性可能会影响球囊毛细胞递质的自发释放。
