Chemosensory glomus cells of the carotid bodies release transmitters, including ATP and dopamine mainly via the exocytosis of small dense core granules (SDCGs, vesicular diameter of ∼100 nm). Using carbon-fiber amperometry, we showed previously that with a modest uniform elevation in cytosolic Ca²⁺ concentration ([Ca²⁺]_i of ∼0.5 µM), SDCGs of rat glomus cells predominantly underwent a “kiss-and-run” mode of exocytosis. Here, we examined whether a larger [Ca²⁺]_i rise influenced the mode of exocytosis. Activation of voltage-gated Ca²⁺ channels by a train of voltage-clamped depolarizations which elevated [Ca²⁺]_i to ∼1.6 μM increased the cell membrane capacitance by ∼2.5%. At 30 s after such a stimulus, only 5% of the added membrane was retrieved. Flash photolysis of caged-Ca²⁺ (which elevated [Ca²⁺]_i to ∼16 μM) increased cell membrane capacitance by ∼13%, and only ∼30% of the added membrane was retrieved at 30 s after the UV flash. When exocytosis and endocytosis were monitored using the two-photon excitation and extracellular polar tracer (TEP) imaging of FM1–43 fluorescence in conjunction with photolysis of caged Ca²⁺, almost uniform exocytosis was detected over the cell’s entire surface and it was followed by slow endocytosis. Immunocytochemistry showed that the cytoplasmic densities of dynamin I, II and clathrin (key proteins that mediate endocytosis) in glomus cells were less than half of those in adrenal chromaffin cells, suggesting that a lower expression of endocytotic machinery may underlie the slow endocytosis in glomus cells. An analysis of the relative change in the signals from two fluorescent dyes that simultaneously monitored the addition of vesicular volume and plasma membrane surface area, suggested that with an intense stimulus, SDCGs of glomus cells underwent full fusion without any significant “compound” exocytosis. Therefore, during a severe hypoxic challenge, glomus granules undergo full fusion for a more complete release of transmitters.

颈动脉体的化学感觉性glomus细胞主要通过小的致密核心颗粒（SDCGs，囊泡直径约100 nm）的胞吐作用释放包括ATP和多巴胺在内的递质。使用碳纤维安培法，我们先前表明，随着胞浆Ca ²⁺浓度的适度均匀升高（[Ca ²⁺ ] _i约为0.5 µM），大鼠小球细胞的SDCG主要经历了“亲吻运行”模式。胞吐作用 在这里，我们检查了较大的[Ca ²⁺ ] _i升高是否影响胞吐作用的模式。通过一系列电压钳制的去极化作用激活电压门控的Ca ²⁺通道，从而提高[Ca ²⁺ ] _i达到约1.6μM，会使细胞膜电容增加约2.5％。刺激后30秒，仅回收了5％的添加膜。笼状Ca ^2+的快速光解（将[Ca ²⁺ ] _i升高至〜16μM）使细胞膜电容增加了约13％，并且在UV闪光后30 s只能回收到约30％的添加膜。当通过FM1–43荧光的双光子激发和细胞外极谱示踪（TEP）成像以及笼养的Ca ^2+的光解作用来监测胞吐和胞吞作用时，在细胞的整个表面上检测到几乎均匀的胞吐作用，然后缓慢的胞吞作用。免疫细胞化学研究显示，肾小球细胞中的动力蛋白I，II和网格蛋白（介导内吞作用的关键蛋白）的细胞质密度不到肾上腺嗜铬细胞中的一半，这表明内吞机制的较低表达可能是慢吞噬作用的基础。分析来自两种荧光染料的信号的相对变化，可同时监测囊泡体积和质膜表面积的增加，表明在强烈刺激下，glomus细胞的SDCGs进行了完全融合，而没有任何明显的“化合物”胞吐作用。因此，在严重的缺氧挑战中，球蛋白颗粒会完全融合，从而使发射器更完整地释放。