Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA.
Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA.
Mol Metab. 2018 Mar;9:84-97. doi: 10.1016/j.molmet.2018.01.016. Epub 2018 Jan 31.
Single-cell RNA sequencing studies have revealed that the type-2 diabetes associated two-pore domain K (K2P) channel TALK-1 is abundantly expressed in somatostatin-secreting δ-cells. However, a physiological role for TALK-1 in δ-cells remains unknown. We previously determined that in β-cells, K flux through endoplasmic reticulum (ER)-localized TALK-1 channels enhances ER Ca leak, modulating Ca handling and insulin secretion. As glucose amplification of islet somatostatin release relies on Ca-induced Ca release (CICR) from the δ-cell ER, we investigated whether TALK-1 modulates δ-cell Ca handling and somatostatin secretion.
To define the functions of islet δ-cell TALK-1 channels, we generated control and TALK-1 channel-deficient (TALK-1 KO) mice expressing fluorescent reporters specifically in δ- and α-cells to facilitate cell type identification. Using immunofluorescence, patch clamp electrophysiology, Ca imaging, and hormone secretion assays, we assessed how TALK-1 channel activity impacts δ- and α-cell function.
TALK-1 channels are expressed in both mouse and human δ-cells, where they modulate glucose-stimulated changes in cytosolic Ca and somatostatin secretion. Measurement of cytosolic Ca levels in response to membrane potential depolarization revealed enhanced CICR in TALK-1 KO δ-cells that could be abolished by depleting ER Ca with sarco/endoplasmic reticulum Ca ATPase (SERCA) inhibitors. Consistent with elevated somatostatin inhibitory tone, we observed significantly reduced glucagon secretion and α-cell Ca oscillations in TALK-1 KO islets, and found that blockade of α-cell somatostatin signaling with a somatostatin receptor 2 (SSTR2) antagonist restored glucagon secretion in TALK-1 KO islets.
These data indicate that TALK-1 reduces δ-cell cytosolic Ca elevations and somatostatin release by limiting δ-cell CICR, modulating the intraislet paracrine signaling mechanisms that control glucagon secretion.
单细胞 RNA 测序研究表明，与 2 型糖尿病相关的双孔域钾 (K2P) 通道 TALK-1 在生长抑素分泌 δ 细胞中大量表达。然而，TALK-1 在 δ 细胞中的生理作用尚不清楚。我们之前确定，在 β 细胞中，通过内质网 (ER) 定位的 TALK-1 通道的 K 流增强 ER Ca 泄漏，调节 Ca 处理和胰岛素分泌。由于胰岛 somatostatin 释放的葡萄糖放大依赖于 δ 细胞 ER 中的 Ca 诱导的 Ca 释放 (CICR)，我们研究了 TALK-1 是否调节 δ 细胞 Ca 处理和 somatostatin 分泌。
为了定义胰岛 δ 细胞 TALK-1 通道的功能，我们生成了表达荧光报告基因的对照和 TALK-1 通道缺陷型 (TALK-1 KO) 小鼠，这些报告基因特异性地在 δ-和 α-细胞中表达，以促进细胞类型鉴定。我们使用免疫荧光、膜片钳电生理学、Ca 成像和激素分泌测定法，评估 TALK-1 通道活性如何影响 δ-和 α-细胞功能。
TALK-1 通道在小鼠和人类 δ 细胞中均有表达，它们调节葡萄糖刺激的细胞溶质 Ca 变化和 somatostatin 分泌。测量膜电位去极化引起的细胞溶质 Ca 水平揭示了 TALK-1 KO δ-细胞中 CICR 的增强，该增强可通过耗尽 ER Ca 与肌浆/内质网 Ca ATP 酶 (SERCA) 抑制剂来消除。与升高的 somatostatin 抑制性张力一致，我们观察到 TALK-1 KO 胰岛中的胰高血糖素分泌和 α-细胞 Ca 振荡明显减少，并且发现用 somatostatin 受体 2 (SSTR2) 拮抗剂阻断 α-细胞 somatostatin 信号可恢复 TALK-1 KO 胰岛中的胰高血糖素分泌。
这些数据表明，TALK-1 通过限制 δ 细胞 CICR 来降低 δ 细胞细胞溶质 Ca 升高和 somatostatin 释放，调节控制胰高血糖素分泌的胰岛内旁分泌信号机制。
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