Ionic conditions modulate stimulus-induced capacitance changes in isolated neurohypophysial terminals of the rat
Ionic conditions modulate stimulus-induced capacitance changes in isolated neurohypophysial terminals of the rat
复制标题
DOI：
10.1113/jphysiol.2009.180778
复制
发表时间：
2010-01-15
影响因子：
5.5
通讯作者：
Lemos, Jose R.
中科院分区：
文献类型：
--
作者：
Marrero, Hector G.;Lemos, Jose R.
神经垂体（NH）的肽能神经末梢在大细胞神经元的肽特异性动作电位刺激下分泌催产素和抗利尿激素。这些脉冲在频率和动作电位持续时间上都有所不同，并且还会在NH末端内外诱导原位离子变化。这些暂时性的影响包括外钾的增加和外钙的减少，以及内钠和氯浓度的增加。为了确定这些离子变化可能对分泌产生的作用机制，在NH的孤立末端使用不同频率和动作电位宽度的动作电位爆发模式进行刺激诱导的电容记录。结果表明，在NH端：(1)增加内氯离子浓度可提高动作电位诱发电容变化的效率；(2)增加外钾离子浓度可提高刺激诱发电容变化的效率；(3)减少外钙离子浓度可降低低频展宽动作电位诱发的电容，而高频非展宽动作电位无电容变化。(4)内钠的增加增加了低频宽动作电位爆发引起的电容变化，比高频窄动作电位爆发引起的电容变化要大。这些结果与先前的刺激诱导分泌模型一致，其中最佳分泌效果是由爆发内动作电位的特定特征决定的。我们的研究结果表明，爆发期间增加的内部钠和外部钾的积极作用可能作为分泌的代偿机制，抵消外部钙减少的负面影响。在这种观点下，高频的未加宽动作电位（初始爆发阶段）会通过增加内钠来调节末梢，以便在加宽动作电位的生理后期最佳分泌。因此，在爆发期间发生的离子变化可能有助于使这种刺激更有效地诱导分泌。此外，这些效应被认为发生在NH神经末梢的催产素和抗利尿激素类型进入爆发活动的最初几秒钟内。
Peptidergic nerve terminals of the neurohypophysis (NH) secrete both oxytocin and vasopressin upon stimulation with peptide-specific bursts of action potentials from magnocellular neurons. These bursts vary in both frequency and action potential duration and also induce in situ ionic changes both inside and outside the terminals in the NH. These temporary effects include the increase of external potassium and decrease of external calcium, as well as the increase in internal sodium and chloride concentrations. In order to determine any mechanism of action that these ionic changes might have on secretion, stimulus-induced capacitance recordings were performed on isolated terminals of the NH using action potential burst patterns of varying frequency and action potential width. The results indicate that in NH terminals: (1) increased internal chloride concentration improves the efficiency of action potential-induced capacitance changes, (2) increasing external potassium increases stimulus-induced capacitance changes, (3) decreasing external calcium decreases the capacitance induced by low frequency broadened action potentials, while no capacitance change is observed with high frequency un-broadened action potentials, and (4) increasing internal sodium increases the capacitance change induced by low frequency bursts of broadened action potentials, more than for high frequency bursts of narrow action potentials. These results are consistent with previous models of stimulus-induced secretion, where optimal secretory efficacy is determined by particular characteristics of action potentials within a burst. Our results suggest that positive effects of increased internal sodium and external potassium during a burst may serve as a compensatory mechanism for secretion, counterbalancing the negative effects of reduced external calcium. In this view, high frequency un-broadened action potentials (initial burst phase) would condition the terminals by increasing internal sodium for optimal secretion by the physiological later phase of broadened action potentials. Thus, ionic changes occurring during a burst may help to make such stimulation more efficient at inducing secretion. Furthermore, these effects are thought to occur within the initial few seconds of incoming burst activity at both oxytocin and vasopressin types of NH nerve terminals.