Hossain Saad Md Zubayer, Xiang Liuruimin, Liao Yan-Shin, Reznikov Leah R, Du Jianyang
Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, United States.
Department of Biological Sciences, University of Toledo, Toledo, OH, United States.
Front Pharmacol. 2021 Feb 2;12:632711. doi: 10.3389/fphar.2021.632711. eCollection 2021.
Transient receptor potential melastatin 3 channel (TRPM3) is a calcium-permeable nonselective cation channel that plays an important role in modulating glucose homeostasis in the pancreatic beta cells. However, how TRPM3 is regulated under physiological and pathological conditions is poorly understood. In this study, we found that both intracellular and extracellular protons block TRPM3 through its binding sites in the pore region. We demonstrated that external protons block TRPM3 with an inhibitory pH of 5.5. whereas internal protons inhibit TRPM3 with an inhibitory pH of 6.9. We identified three titratable residues, D1059, D1062, and D1073, at the vestibule of the channel pore that contributes to pH sensitivity. The mutation of D1073Q reduced TRPM3 current by low external pH 5.5 from 62 ± 3% in wildtype to 25 ± 6.0% in D1073Q mutant. These results indicate that D1073 is essential for pH sensitivity. In addition, we found that a single mutation of D1059 or D1062 enhanced pH sensitivity. In summary, our findings identify molecular determinants respionsible for the pH regulation of TRPM3. The inhibition of TRPM3 by protons may indicate an endogenous mechanism governing TRPM3 gating and its physiological/pathological functions.
瞬时受体电位褪黑素3通道（TRPM3）是一种钙通透性非选择性阳离子通道，在调节胰腺β细胞的葡萄糖稳态中起重要作用。然而，人们对TRPM3在生理和病理条件下如何被调节知之甚少。在本研究中，我们发现细胞内和细胞外的质子通过其在孔区域的结合位点阻断TRPM3。我们证明外部质子以pH 5.5的抑制性pH值阻断TRPM3，而内部质子以pH 6.9的抑制性pH值抑制TRPM3。我们在通道孔的前庭确定了三个可滴定残基D1059、D1062和D1073，它们有助于pH敏感性。D1073Q突变使低外部pH 5.5时的TRPM3电流从野生型的62±3%降低到D1073Q突变体的25±6.0%。这些结果表明D1073对pH敏感性至关重要。此外，我们发现D1059或D1062的单一突变增强了pH敏感性。总之，我们的研究结果确定了负责TRPM3 pH调节的分子决定因素。质子对TRPM3的抑制可能表明一种控制TRPM3门控及其生理/病理功能的内源性机制。
