Walker R L, Hume J R, Horowitz B
Department of Physiology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
Am J Physiol Cell Physiol. 2001 May;280(5):C1184-92. doi: 10.1152/ajpcell.2001.280.5.C1184.
Nonselective cation channels (NSCC) are targets of excitatory agonists in smooth muscle, representing the nonselective cation current I(cat). Na(+) influx through NSCC causes depolarizations and activates voltage-dependent Ca(2+) channels, resulting in contraction. The molecular identity of I(cat) in smooth muscle has not been elucidated; however, products of the transient receptor potential (TRP) genes have characteristics similar to native I(cat). We have determined the levels of TRP transcriptional expression in several murine and canine gastrointestinal and vascular smooth muscles and have analyzed the alternative processing of these transcripts. Of the seven TRP gene family members, transcripts for TRP4, TRP6, and TRP7 were detected in all murine and canine smooth muscle cell preparations. TRP3 was detected only in canine renal artery smooth muscle cells. The full-length cDNAs for TRP4, TRP6, and TRP7, as well as one splice variant of TRP4 and two splice variants of TRP7, were cloned from murine colonic smooth muscle. Quantitative RT-PCR determined the relative amounts of TRP4, TRP6, and TRP7 transcripts, as well as that of the splice variants, in several murine smooth muscles. TRP4 is the most highly expressed, while TRP6 and TRP7 are expressed at a lower level in the same tissues. Splice variants for TRP7, deleted for exons encoding amino acids including transmembrane segment S1, predominated in murine smooth muscles, while the full-length form of the transcript was expressed in canine smooth muscles.
非选择性阳离子通道（NSCC）是平滑肌中兴奋性激动剂的作用靶点，代表非选择性阳离子电流I（cat）。通过NSCC的Na（+）内流导致去极化并激活电压依赖性Ca（2+）通道，从而引起收缩。平滑肌中I（cat）的分子身份尚未阐明；然而，瞬时受体电位（TRP）基因的产物具有与天然I（cat）相似的特征。我们已经确定了几种小鼠和犬类胃肠道及血管平滑肌中TRP转录表达的水平，并分析了这些转录本的可变剪接。在七个TRP基因家族成员中，在所有小鼠和犬类平滑肌细胞制剂中均检测到TRP4、TRP6和TRP7的转录本。仅在犬肾动脉平滑肌细胞中检测到TRP3。从鼠结肠平滑肌中克隆了TRP4、TRP6和TRP7的全长cDNA，以及TRP4的一个剪接变体和TRP7的两个剪接变体。定量RT-PCR确定了几种小鼠平滑肌中TRP4、TRP6和TRP7转录本以及剪接变体的相对含量。TRP4表达最高，而TRP6和TRP7在相同组织中的表达水平较低。在小鼠平滑肌中，缺失编码包括跨膜段S1在内的氨基酸的外显子的TRP7剪接变体占主导地位，而转录本的全长形式则在犬平滑肌中表达。
