Pancreatic β-cells release insulin upon a rise in blood glucose. The precise mechanisms of stimulus-secretion coupling, and its failure in Diabetes Mellitus Type 2, remain to be elucidated. The consensus model, as well as a class of currently prescribed anti-diabetic drugs, are based around the observation that glucose-evoked ATP production in β-cells leads to closure of cell membrane ATP-gated potassium (K_ATP) channels, plasma membrane depolarisation, Ca²⁺ influx, and finally the exocytosis of insulin granules (Ashcroft et al., 1984; Cook and Hales, 1984). However, it has been demonstrated by the inactivation of this pathway using genetic and pharmacological means that closure of the K_ATP channel alone may not be sufficient to explain all β-cell responses to glucose elevation (Henquin, 1998; Seghers et al., 2000). Here we show using total internal reflection fluorescence (TIRF) microscopy (Axelrod, 1981) that glucose as well as the Ca²⁺ mobilising messenger nicotinic acid adenine dinucleotide phosphate (NAADP), known to operate in β-cells (Johnson and Misler, 2002; Masgrau et al., 2003), lead to highly localised elementary intracellular Ca²⁺ signals. These were found to be obscured by measurements of global Ca²⁺ signals and the action of powerful SERCA-based sequestration mechanisms at the endoplasmic reticulum (ER). This is the first demonstration of elemental Ca²⁺ signals in response to NAADP, although they have been suspected (Davis et al., 2020). Optical quantal analysis of these events reveals a unitary event amplitude equivalent to that of known elementary Ca²⁺ signalling events, inositol trisphosphate (IP₃) receptor mediated blips (Parker et al., 1996; Parker and Ivorra, 1990), and ryanodine receptor mediated sparks (Cheng et al., 1993). We propose that a mechanism based on these highly localised intracellular Ca²⁺ signalling events mediated by NAADP may initially operate in β-cells when they respond to elevations in blood glucose.

中文翻译：

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葡萄糖和NAADP触发基本的细胞内β细胞Ca2 +信号

血糖升高时，胰腺β细胞会释放胰岛素。刺激-分泌耦合的精确机制及其在2型糖尿病中的失败仍有待阐明。共识模型以及当前开出的一类抗糖尿病药物均基于以下观察结果：β细胞中葡萄糖诱发的ATP产生导致细胞膜ATP门控钾（K _ATP）通道，质膜的关闭去极化，Ca ²⁺流入，最后是胰岛素颗粒的胞吐作用（Ashcroft等，1984； Cook and Hales，1984）。但是，已通过遗传和药理学方法证实该途径的失活证明了K _ATP的关闭单独的通道可能不足以解释所有β细胞对葡萄糖升高的反应（Henquin，1998； Seghers等，2000）。在这里我们使用全内反射荧光（TIRF）显微镜（Axelrod，1981）显示葡萄糖以及Ca ²⁺动员信使烟酸腺嘌呤二核苷酸磷酸（NAADP），已知在β细胞中起作用（Johnson和Misler，2002年）。 ； Masgrau等人，2003），导致高度局部化的基本细胞内Ca ²⁺信号。发现这些被整体Ca ²⁺信号的测量以及内质网（ER）上基于SERCA的强大螯合机制的作用所掩盖。这是元素Ca ²⁺的首次演示尽管有人怀疑它们对NAADP有反应（Davis等，2020）。这些事件的光学定量分析显示，单一事件的幅度等于已知的基本Ca ²⁺信号事件，肌醇三磷酸（IP ₃）受体介导的斑点（Parker et al。，1996; Parker and Ivorra，1990）和ryanodine受体的幅度。介导的火花（Cheng等，1993）。我们提出，基于NAADP介导的这些高度定位的细胞内Ca ²⁺信号事件的机制，当它们响应血糖升高时，可能最初在β细胞中起作用。