Department of Physiology and Biophysics, VCU Program in Enteric Neuromuscular Sciences, Virginia Commonwealth University, Richmond, VA, USA.
Neurogastroenterol Motil. 2020 Feb;32(2):e13737. doi: 10.1111/nmo.13737. Epub 2019 Nov 12.
l-amino acids, such as monosodium glutamate (MSG), activate the umami receptor T1R1/T1R3. We previously showed increased peristalsis in response to activation of T1R1/T1R3 by MSG in mouse colon. However, the expression and function of these receptors in the different regions of the stomach are not clear.
Mouse gastric smooth muscle cells (SMCs) were isolated and cultured in Dulbecco's Modified Eagle Medium. Expression of T1R1 and T1R3 was measured by RT-PCR and Western blot. The effect of MSG with and without inosine monophosphate (IMP, an allosteric activator of T1R1/T1R3) on acetylcholine (ACh)-induced contraction was measured in muscle strips and isolated SMCs by scanning micrometry. The effect of MSG with or without IMP on activation of G proteins and ACh-induced Ca release was measured in SMCs.
Monosodium glutamate inhibited ACh-induced contractions in muscle strips from both antrum and fundus and the effect of MSG was augmented by IMP; the effects were concentration-dependent and not affected by the nitric oxide synthase inhibitor, L-NNA, or tetrodotoxin suggesting a direct effect on SMCs. In isolated gastric SMCs, T1R1 and T1R3 transcripts and protein were identified. Addition of MSG with or without IMP inhibited ACh-induced Ca release and muscle contraction; the effect on contraction was blocked by pertussis toxin suggesting activation of Gα proteins. MSG in the presence of IMP selectively activated Gα .
Umami receptors (T1R1/T1R3) are present on SMCs of the stomach, and activation of these receptors induces muscle relaxation by decreasing [Ca ] via Gα .
l-氨基酸，如谷氨酸单钠（MSG），可激活鲜味受体 T1R1/T1R3。我们之前的研究表明，在小鼠结肠中，MSG 通过激活 T1R1/T1R3 可增加蠕动。然而，这些受体在胃的不同区域的表达和功能尚不清楚。
从小鼠胃平滑肌细胞（SMCs）中分离并在 Dulbecco 改良 Eagle 培养基中培养。通过 RT-PCR 和 Western blot 测量 T1R1 和 T1R3 的表达。使用扫描微测法在肌条和分离的 SMC 中测量 MSG（鲜味受体的激动剂）与肌苷酸（IMP，T1R1/T1R3 的别构激活剂）共同作用或分别作用对乙酰胆碱（ACh）诱导的收缩的影响。在 SMC 中测量 MSG 与或不与 IMP 对 G 蛋白的激活和 ACh 诱导的 Ca 释放的影响。
MSG 抑制了来自胃窦和胃底的肌条中 ACh 诱导的收缩，IMP 增强了 MSG 的作用；这种作用具有浓度依赖性，不受一氧化氮合酶抑制剂 L-NNA 或河豚毒素的影响，表明其对 SMC 具有直接作用。在分离的胃 SMC 中，鉴定出 T1R1 和 T1R3 的转录本和蛋白质。加入 MSG 与或不与 IMP 抑制了 ACh 诱导的 Ca 释放和肌肉收缩；这种收缩作用被百日咳毒素阻断，表明 Gα 蛋白被激活。IMP 存在时 MSG 选择性地激活 Gα 。
鲜味受体（T1R1/T1R3）存在于胃的 SMC 上，这些受体的激活通过降低[Ca]来诱导肌肉松弛，从而通过 Gα 实现。
