Ghrelin uses Gαi2 and activates voltage-dependent K+ channels to attenuate glucose-induced Ca2+ signaling and insulin release in islet β-cells -: Novel signal transduction of ghrelin
Ghrelin uses Gαi2 and activates voltage-dependent K+ channels to attenuate glucose-induced Ca2+ signaling and insulin release in islet β-cells -: Novel signal transduction of ghrelin
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DOI：
10.2337/db07-0345
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发表时间：
2007-09-01
期刊：
影响因子：
7.7
通讯作者：
Yada, Toshihiko
中科院分区：
文献类型：
--
作者：
Dezaki, Katsuya;Kakei, Masafumi;Yada, Toshihiko
据报道，胃饥饿素是胰岛素释放的一种生理调节剂。本研究旨在探索胰岛β细胞中胃饥饿素抑制胰岛素作用的信号机制，特别关注异源三聚体GTP结合蛋白和K⁺通道。采用酶联免疫吸附测定（ELISA）法测定大鼠血浆胰岛素和生长激素（GH）浓度。通过胶原酶消化从大鼠、胃饥饿素基因敲除（Ghr - KO）小鼠和野生型小鼠中分离胰岛，并用ELISA测定胰岛素释放。在大鼠单个β细胞中，采用fura - 2微量荧光测定法测量胞质Ca²⁺浓度（[Ca²⁺]₍ᵢ₎），采用膜片钳技术测量膜电位和全细胞电流。在大鼠中，全身性给予胃饥饿素可降低血浆胰岛素浓度，这种作用可被百日咳毒素（PTX）处理所阻断，而对生长激素释放的刺激则不受影响。在大鼠胰岛中，胃饥饿素受体拮抗剂以对PTX敏感的方式增加葡萄糖诱导的胰岛素释放，外源性胃饥饿素则抑制该释放。从胰岛释放的葡萄糖诱导的胰岛素在Ghr - KO小鼠中比野生型小鼠更多，且这种增强的分泌可被PTX减弱。胃饥饿素以对PTX敏感的方式增加电压依赖性K⁺（Kv）电流，而不影响大鼠β细胞中的ATP敏感性K⁺通道。在存在Kv通道阻滞剂的情况下，胃饥饿素无法抑制胰岛素释放。胃饥饿素减弱β细胞中葡萄糖诱导的动作电位和[Ca²⁺]₍ᵢ₎的增加。在经PTX处理以及用针对G蛋白Gα₍ᵢ₂₎亚基的反义寡核苷酸处理的β细胞中，胃饥饿素对[Ca²⁺]₍ᵢ₎增加和胰岛素释放的抑制作用减弱。胃饥饿素通过对PTX敏感的Gα₍ᵢ₂₎介导的Kv通道激活以及对β细胞中[Ca²⁺]₍ᵢ₎的抑制来减弱葡萄糖诱导的胰岛素释放，这代表了胃饥饿素不同于生长激素释放的独特信号传导。
Ghrelin reportedly serves as a physiological regulator of insulin release. This study aimed to explore signaling mechanisms for insulinostatic ghrelin action in islet beta-cells, with special attention to heterotrimeric GTP-binding proteins and K+ channels. Plasma insulin and growth hormone (GH) concentrations in rats were measured by enzyme-linked immunosorbent assay (ELISA). Islets were isolated from rats, ghrelin-knockout (Ghr-KO) mice, and wild-type mice by collagenase digestion, and insulin release was determined by ELISA. In rat single beta-cells, cytosolic Ca2+ concentration ([Ca2+](i)) was measured by fura-2 microfluorometry, and membrane potentials and whole cell currents by patch-clamp technique. In rats, systemic ghrelin administration decreased plasma insulin concentrations, and this effect was blocked by treatment with pertussis toxin (PTX), whereas stimulation of GH,release remained unaffected. In rat islets, ghrelin receptor antagonist increased and exogenous ghrelin suppressed glucose-induced insulin release in a PTX-sensitive manner. Glucose-induced insulin release from islets was greater in Ghr-KO than wild-type mice, and this enhanced secretion was blunted with PTX. Ghrelin PTX sensitively increased voltage-dependent K+ (Kv) currents without affecting ATP-sensitive K+ channels in rat R-cells. In the presence of Kv channel blockers, ghrelin failed to suppress insulin release. Ghrelin attenuated glucose-induced action potentials and [Ca2+](i) increases in P-cells. Suppressions of [Ca2+](i) increase and insulin release by ghrelin were blunted in P-cells treated with PTX and with antisense oligonucleotide specific for G-protein G alpha(i2)-subunit. Ghrelin attenuates glucose-induced insulin release via PTX-sensitive G alpha(i2)-mediated activation of Kv channels and suppression of [Ca2+](i) in beta-cells, representing the unique signaling of ghrelin distinct from that for GH release.