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 intracellular binding sites. We demonstrated that external protons indirectly block TRPM3, whereas internal protons inhibit TRPM3 directly with an inhibitory pH50 of 6.9. We identified three titratable residues, D1059, D1062, and D1073, at the inner vestibule of the channel pore that contributes to pH sensitivity. The mutation of D1073Q reduces TRPM3 current intensity and pH sensitivity; Replacement of Asp 1073 by Gln 1073 changes the reduction of TRPM3 outward current by low external pH 5.5, from 62% in WT to 25% in D1073Q. These results indicate that D1073 is not only essential for intracellular pH sensitivity, but it is also crucial for TRPM3 channel gating. In addition, a single mutation of D1059 or D1062 enhances pH sensitivity. In summary, our findings provide a novel molecular determinant for pH regulation of TRPM3. The inhibition of TRPM3 by protons may indicate an endogenous mechanism governing TRPM3 gating and its physiological/ pathological functions.

中文翻译：

---

质子通过其细胞内结合位点调节瞬时受体电位褪黑素3

瞬时受体电位褪黑素3通道（TRPM3）是钙可渗透的非选择性阳离子通道，在调节胰岛β细胞的葡萄糖稳态中起重要作用。然而，人们对如何在生理和病理条件下调节TRPM3知之甚少。在这项研究中，我们发现细胞内和细胞外质子均通过其细胞内结合位点阻断TRPM3。我们证明了外部质子间接阻断TRPM3，而内部质子直接抑制TRPM3，其抑制pH50为6.9。我们在通道孔的内部前庭中发现了三个可滴定的残基D1059，D1062和D1073，这有助于pH敏感性。D1073Q的突变降低了TRPM3的电流强度和pH敏感性；用Gln 1073替代Asp 1073，可通过较低的外部pH 5.5改变TRPM3向外电流的降低，从WT中的62％降低到D1073Q中的25％。这些结果表明，D1073不仅对细胞内pH敏感性至关重要，而且对TRPM3通道门控也至关重要。此外，D1059或D1062的单个突变可增强pH敏感性。总之，我们的发现为TRPM3的pH调节提供了一个新的分子决定因素。质子对TRPM3的抑制可能表明控制TRPM3门控及其生理/病理功能的内源性机制。D1059或D1062的单个突变可增强pH敏感性。总之，我们的发现为TRPM3的pH调节提供了一个新的分子决定因素。质子对TRPM3的抑制可能表明控制TRPM3门控及其生理/病理功能的内源性机制。D1059或D1062的单个突变可增强pH敏感性。总之，我们的发现为TRPM3的pH调节提供了一个新的分子决定因素。质子对TRPM3的抑制可能表明控制TRPM3门控及其生理/病理功能的内源性机制。