Maruyama Yoshiaki, Nakanishi Yuko, Walsh Emma J, Wilson David P, Welsh Donald G, Cole William C
Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, Alberta, Canada.
Circ Res. 2006 Jun 23;98(12):1520-7. doi: 10.1161/01.RES.0000226495.34949.28. Epub 2006 May 11.
The molecular identity of receptor-operated, nonselective cation channels (ROCs) of vascular smooth muscle (VSM) cells is not known for certain. Mammalian homologues of the Drosophila canonical transient receptor potential channels (TRPCs) are possible candidates. This study tested the hypothesis that heteromultimeric TRPC channels contribute to ROC current of A7r5 VSM cells activated by [Arg(8)]-vasopressin. A7r5 cells expressed transcripts encoding TRPC1, TRPC4beta, TRPC6, and TRPC7. TRPC4, TRPC6, and TRPC7 protein expression was confirmed by immunoblotting and association of TRPC6 with TRPC7, but not TRPC4beta, was detected by coimmunoprecipitation. The amplitude of arginine vasopressin (AVP)-induced ROC current was suppressed by dominant-negative mutant TRPC6 (TRPC6(DN)) but not TRPC5 (TRPC5(DN)) mutant subunit expression. These data indicate a role for TRPC6- and/or TRPC7-containing channels and rule a more complex subunit composition including TRPC1 and TRPC4. Increasing extracellular Ca(2+) concentration (Ca(2+)) from 0.05 to 1 mmol/L suppressed currents owing to native, TRPC7, and heteromultimeric TRPC6-TRPC7 channels, but not TRPC6 current, which was slightly enhanced. The relative changes in native and heteromultimeric TRPC6-TRPC7 current amplitudes for Ca(2+) between approximately 0.01 and 1 mmol/L were identical, but the changes in homomultimeric TRPC6 and TRPC7 currents were significantly less and greater, respectively, compared with the native channels. Taken together, the data provide biochemical and functional evidence supporting the view that heteromultimeric TRPC6-TRPC7 channels contribute to receptor-activated, nonselective cation channels of A7r5 VSM cells.
血管平滑肌（VSM）细胞中受体操纵的非选择性阳离子通道（ROC）的分子特性尚未完全明确。果蝇经典瞬时受体电位通道（TRPC）的哺乳动物同源物可能是候选对象。本研究检验了以下假说：异源多聚体TRPC通道参与了由[精氨酸（8）] - 血管加压素激活的A7r5 VSM细胞的ROC电流。A7r5细胞表达编码TRPC1、TRPC4β、TRPC6和TRPC7的转录本。通过免疫印迹证实了TRPC4、TRPC6和TRPC7蛋白的表达，并且通过共免疫沉淀检测到TRPC6与TRPC7而非TRPC4β的结合。精氨酸血管加压素（AVP）诱导的ROC电流幅度被显性负性突变体TRPC6（TRPC6（DN））抑制，但未被TRPC5（TRPC5（DN））突变亚基的表达所抑制。这些数据表明含TRPC6和/或TRPC7的通道发挥了作用，并排除了包括TRPC1和TRPC4在内的更复杂亚基组成。将细胞外钙浓度（[Ca（2 +）]（o））从0.05 mmol/L增加到1 mmol/L会抑制天然通道、TRPC7以及异源多聚体TRPC6 - TRPC7通道的电流，但不会抑制TRPC6电流，反而会使其略有增强。在大约0.01至1 mmol/L之间，[Ca（2 +）]（o）变化时，天然通道和异源多聚体TRPC6 - TRPC7电流幅度的相对变化是相同的，但与天然通道相比，同型多聚体TRPC6和TRPC7电流的变化分别明显更小和更大。综上所述，这些数据提供了生化和功能证据，支持异源多聚体TRPC6 - TRPC7通道参与A7r5 VSM细胞受体激活的非选择性阳离子通道的观点。
