Soldo Brandi L, Giovannucci David R, Stuenkel Edward L, Moises Hylan C
Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
J Physiol. 2004 Mar 16;555(Pt 3):699-711. doi: 10.1113/jphysiol.2003.051136. Epub 2003 Nov 28.
In addition to action potential-evoked exocytotic release at neurohypophysial nerve terminals, the neurohormones arginine vasopressin (aVP) and oxytocin (OT) undergo Ca(2+)-dependent somatodendritic release within the supraoptic and paraventricular hypothalamic nuclei. However, the cellular and molecular mechanisms that underlie this release have not been elucidated. In the present study, the whole-cell patch-clamp technique was utilized in combination with high-time-resolved measurements of membrane capacitance (C(m)) and microfluorometric measurements of cytosolic free Ca(2+) concentration (Ca(2+)) to examine the Ca(2+) and stimulus dependence of exocytosis in the somata of magnocellular neurosecretory cells (MNCs) isolated from rat supraoptic nucleus (SON). Single depolarizing steps (> or =20 ms) that evoked high-voltage-activated (HVA) Ca(2+) currents (I(Ca)) and elevations in intracellular Ca(2+) concentration were accompanied by an increase in C(m) in a majority (40/47) of SON neurones. The C(m) responses were composed of an initial Ca(2+)-independent, transient component and a subsequent, sustained phase of increased C(m) (termed DeltaC(m)) mediated by an influx of Ca(2+), and increased with corresponding prolongation of depolarizing step durations (20-200 ms). From this relationship we estimated the rate of vesicular release to be 1533 vesicles s(-1). Delivery of neurone-derived action potential waveforms (APWs) as stimulus templates elicited I(Ca) and also induced a DeltaC(m), provided APWs were applied in trains of greater than 13 Hz. A train of APWs modelled after the bursting pattern recorded from an OT-containing neurone during the milk ejection reflex was effective in supporting an exocytotic DeltaC(m) in isolated MNCs, indicating that the somata of SON neurones respond to physiological patterns of neuronal activity with Ca(2+)-dependent exocytotic activity.
除了在神经垂体神经末梢动作电位诱发的胞吐释放外，神经激素精氨酸加压素（aVP）和催产素（OT）还会在下丘脑视上核和室旁核内经历钙依赖性的树突体释放。然而，这种释放背后的细胞和分子机制尚未阐明。在本研究中，全细胞膜片钳技术与膜电容（C(m)）的高时间分辨率测量以及胞质游离钙浓度（Ca(2+)）的显微荧光测量相结合，以研究从大鼠视上核（SON）分离的大细胞神经分泌细胞（MNCs）胞体中胞吐作用对钙和刺激的依赖性。诱发高电压激活（HVA）钙电流（I(Ca)）和细胞内钙浓度升高的单个去极化步骤（≥20毫秒），在大多数（40/47）SON神经元中伴随着C(m)的增加。C(m)反应由初始的钙非依赖性瞬时成分和随后由钙内流介导的C(m)持续增加阶段（称为ΔC(m)）组成，并随着去极化步骤持续时间（20 - 200毫秒）的相应延长而增加。根据这种关系，我们估计囊泡释放速率为1533个囊泡·秒(-1)。作为刺激模板传递神经元衍生的动作电位波形（APWs）会诱发I(Ca)，并且只要APWs以大于13 Hz的序列施加，也会诱导ΔC(m)。在排乳反射期间从含OT的神经元记录的爆发模式模拟的APWs序列，有效地支持了分离的MNCs中的胞吐性ΔC(m)，表明SON神经元的胞体对神经元活动的生理模式具有钙依赖性胞吐活性反应。
