Lin J-W, Fu Q
Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA.
Neuroscience. 2005;130(4):889-95. doi: 10.1016/j.neuroscience.2004.10.023.
We have investigated the effect of serotonin (5-HT) and okadaic acid (OA) on presynaptic processes at the crayfish inhibitory neuromuscular junction. Two different physiological parameters of transmitter release were examined: release kinetics and the size of the readily releasable pool of vesicles (RRP). Using a paired pulse stimulus and high frequency trains, we established that a single broad action potential, recorded in 20 mM tetraethylammonium and 1 mM 4-amino-pyridine, released the RRP in its entirety. Thus, by measuring the amplitude of inhibitory postsynaptic potential (IPSC) we were able to directly assess the effects of 5-HT and OA on the RRP. Serotonin at 200 nM and OA at 2.5 microM each significantly increased IPSC above control levels and the effects of these two modulators were comparable. Both modulators also induced a leftward shift in the rising phase of IPSC, i.e. an apparent acceleration in release kinetics. The shift caused by OA was significantly more pronounced than that induced by 5-HT. This apparent acceleration in release was not associated with a corresponding change in the presynaptic Ca2+ transient measured at a 2 kHz resolution, suggesting that modulation was not due to an acceleration in Ca2+ channel kinetics. In view of the comparable increase in the size of the RRP by the modulators, the differential modulation of release kinetics suggests that these two parameters may be modulated by separate biochemical processes.
我们研究了血清素(5-羟色胺,5-HT)和冈田酸(OA)对小龙虾抑制性神经肌肉接头处突触前过程的影响。我们检测了递质释放的两个不同生理参数:释放动力学以及囊泡的易释放池(RRP)大小。使用双脉冲刺激和高频串刺激,我们确定,在含有20 mM四乙铵和1 mM 4-氨基吡啶的溶液中记录到的单个宽动作电位可完全释放RRP。因此,通过测量抑制性突触后电位(IPSC)的幅度,我们能够直接评估5-HT和OA对RRP的影响。200 nM的5-HT和2.5 μM的OA均使IPSC显著高于对照水平,且这两种调节剂的作用相当。两种调节剂还使IPSC上升相向左移位,即释放动力学明显加快。OA引起的移位比5-HT引起的更明显。这种明显的释放加速与以2 kHz分辨率测量的突触前Ca2+瞬变的相应变化无关,这表明调节并非由于Ca2+通道动力学加速所致。鉴于调节剂使RRP大小有相当程度的增加,释放动力学的差异调节表明这两个参数可能由不同的生化过程调节。