Cheng Jinbo, Jackson Meyer B
Department of Neuroscience and Biophysics PhD Program, University of Wisconsin-Madison, Madison, WI, USA.
J Physiol. 2024 Aug 14. doi: 10.1113/JP286175.
Somatostatin, a peptide hormone that activates G-protein-coupled receptors, inhibits the secretion of many hormones. This study investigated the mechanisms of this inhibition using amperometry recording of Ca-triggered catecholamine secretion from mouse chromaffin cells. Two distinct stimulation protocols, high-KCl depolarization and caffeine, were used to trigger exocytosis, and confocal fluorescence imaging was used to monitor the rise in intracellular free Ca. Analysis of single-vesicle fusion events (spikes) resolved the action of somatostatin on fusion pores at different stages. Somatostatin reduced spike frequency, and this reduction was accompanied by prolongation of pre-spike feet and slowing of spike rise times. This indicates that somatostatin stabilizes initial fusion pores and slows their expansion. This action on the initial fusion pore impacted the release mode to favour kiss-and-run over full-fusion. During a spike the permeability of a fusion pore peaks, declines and then settles into a plateau. Somatostatin had no effect on the plateau, suggesting no influence on late-stage fusion pores. These actions of somatostatin were indistinguishable between exocytosis triggered by high-KCl and caffeine, and fluorescence imaging showed that somatostatin had no effect on stimulus-induced rises in cytosolic Ca. Our findings thus demonstrate that the signalling cascades activated by somatostatin target the exocytotic machinery that controls the initial and expanding stages of fusion pores, while having no effect on late-stage fusion pores. As a result of its stronger inhibition of full-fusion compared to kiss-and-run, somatostatin will preferentially inhibit the secretion of large peptides over the secretion of small catecholamines. KEY POINTS: Somatostatin inhibits the secretion of various hormones by activating G-protein-coupled receptors. In this study, we used amperometry to investigate the mechanism by which somatostatin inhibits catecholamine release from mouse chromaffin cells. Somatostatin increased pre-spike foot lifetime and slowed fusion pore expansion. Somatostatin inhibited full-fusion more strongly than kiss-and-run. Our results suggest that the initial fusion pore is the target of somatostatin-mediated regulation of hormone release. The stronger inhibition of full-fusion by somatostatin will result in preferential inhibition of peptide release.
生长抑素是一种能激活G蛋白偶联受体的肽类激素，可抑制多种激素的分泌。本研究利用安培法记录小鼠嗜铬细胞中钙触发的儿茶酚胺分泌，探究了这种抑制作用的机制。采用两种不同的刺激方案，即高钾 depolarization 和咖啡因，来触发胞吐作用，并利用共聚焦荧光成像监测细胞内游离钙的升高。对单囊泡融合事件（尖峰）的分析解析了生长抑素在不同阶段对融合孔的作用。生长抑素降低了尖峰频率，且这种降低伴随着尖峰前足部的延长和尖峰上升时间的减慢。这表明生长抑素稳定了初始融合孔并减缓了它们的扩张。这种对初始融合孔的作用影响了释放模式，使其更倾向于“亲吻-逃离”而非完全融合。在一个尖峰期间，融合孔的通透性先达到峰值，然后下降，最后稳定在一个平台期。生长抑素对平台期没有影响，表明对后期融合孔没有影响。生长抑素的这些作用在高钾和咖啡因触发的胞吐作用之间没有区别，荧光成像显示生长抑素对刺激诱导的胞质钙升高没有影响。因此，我们的研究结果表明，生长抑素激活的信号级联靶向控制融合孔初始和扩张阶段的胞吐机制，而对后期融合孔没有影响。由于与“亲吻-逃离”相比，生长抑素对完全融合的抑制更强，因此它将优先抑制大肽的分泌而非小儿茶酚胺的分泌。要点：生长抑素通过激活G蛋白偶联受体抑制多种激素的分泌。在本研究中，我们利用安培法探究生长抑素抑制小鼠嗜铬细胞释放儿茶酚胺的机制。生长抑素增加了尖峰前足部的寿命并减缓了融合孔的扩张。生长抑素对完全融合的抑制比对“亲吻-逃离”更强。我们的结果表明，初始融合孔是生长抑素介导的激素释放调节的靶点。生长抑素对完全融合的更强抑制将导致对肽释放的优先抑制。
