Towards understanding physiological function of TRPM6/7 like channel in a HCO_3-secreting epithelium

反刍动物腮腺即使在休息时也能持续分泌大量富含HCO3的唾液，但其潜在的分子机制尚不清楚。由于反刍动物腮腺分泌细胞含有多个可受细胞内钙离子和镁离子调节的离子通道，这些二价阳离子的静息动态平衡也可能在持续的HCO3分泌中起重要作用。为了更好地了解腮腺HCO3分泌的机制，本项目重点研究了TRPM6和TRPM7，它们是已知的对二价阳离子(如Ca^&lt；2+&gt；和Mg^&lt；2+&gt；)具有通透性的阳离子通道。利用电生理和分子生物学技术发现：1)牛腮腺腺泡细胞具有膜电流，该电流对重组的TRPM7和TRPM6电流敏感；2)牛腮腺细胞表达TRPM6和TRPM7转录本；3)从牛腮腺克隆的TRPM7在异源表达系统中具有功能。这些基本结果将有助于进一步研究牛腮腺腺泡细胞天然TRPM6/7样电导的分子基础和细胞调控，以及TRPM6和TRPM7在上皮HCO3分泌中的作用。

Ruminant parotid glands secrete continuously large volumes of HCO_3-rich saliva even at resting, but the underlying molecular mechanism remains unclear. Since ruminant parotid secretory cells contain several ion channels that can be regulated by intracellular Ca^<2+> and Mg^<2+>, resting cellular homeostasis of these divalent cations might also play an important role in the continuous HCO_3 secretion. Towards better understanding the mechanism of the parotid HCO_3 secretion, this project focused on TRPM6 and TRPM7 that are known to be cation channels permeable to divalent cations such as Ca^<2+> and Mg^<2+>. Using electrophysiological and molecular biological techniques, it was found that 1) bovine parotid acinar cells exhibit a membrane current, which is sensitive to intracellular Mg^<2+> as reported for recombinant TRPM7 and TRPM6 currents, 2) bovine parotid cells express transcripts of TRPM6 and TRPM7, 3) TRPM7 that was cloned from bovine parotid was functional in a heterologous expression system. These basic results would be useful for future studies to address the issues as to not only the molecular basis and cellular regulation of the native TRPM6/7-like conductance in bovine parotid acinar cells, but also the role of TRPM6 and TRPM7 in epithelial HCO_3 secretion.