He Tao, Nitabach Michael N, Lnenicka Gregory A
a Division of Pulmonary and Critical Care Medicine , David Geffen School of Medicine at UCLA , Los Angeles , CA , USA.
b Department of Cellular and Molecular Physiology , Yale School of Medicine , New Haven , CT , USA.
J Neurogenet. 2018 Sep;32(3):209-220. doi: 10.1080/01677063.2018.1498496. Epub 2018 Sep 3.
Presynaptic Ca appears to play multiple roles in synaptic development and physiology. We examined the effect of buffering presynaptic Ca by expressing parvalbumin (PV) in Drosophila neurons, which do not normally express PV. The studies were performed on the identified Ib terminal that innervates muscle fiber 5. The volume-averaged, residual Ca resulting from single action potentials (APs) and AP trains was measured using the fluorescent Ca indicator, OGB-1. PV reduced the amplitude and decay time constant (τ) for single-AP Ca transients. For AP trains, there was a reduction in the rate of rise and decay of [Ca] but the plateau [Ca] was not affected. Electrophysiological recordings from muscle fiber 5 showed a reduction in paired-pulse facilitation, particularly the F component; this was likely due to the reduction in residual Ca. These synapses also showed reduced synaptic enhancement during AP trains, presumably due to less buildup of synaptic facilitation. The transmitter release for single APs was increased for the PV-expressing terminals and this may have been a homeostatic response to the decrease in facilitation. Confocal microscopy was used to examine the structure of the motor terminals and PV expression resulted in smaller motor terminals with fewer synaptic boutons and active zones. This result supports earlier proposals that increased AP activity promotes motor terminal growth through increases in presynaptic [Ca].
突触前钙离子似乎在突触发育和生理学中发挥多种作用。我们通过在通常不表达小白蛋白（PV）的果蝇神经元中表达小白蛋白来研究缓冲突触前钙离子的作用。这些研究是在支配肌肉纤维5的已鉴定的Ib终末上进行的。使用荧光钙指示剂OGB-1测量单个动作电位（AP）和AP串产生的体积平均残余钙。PV降低了单个AP钙瞬变的幅度和衰减时间常数（τ）。对于AP串，[Ca]的上升和衰减速率降低，但平台期[Ca]不受影响。对肌肉纤维5的电生理记录显示双脉冲易化降低，尤其是F成分；这可能是由于残余钙减少所致。这些突触在AP串期间也显示出突触增强减弱，推测是由于突触易化的积累较少。对于表达PV的终末，单个AP的递质释放增加，这可能是对易化降低的一种稳态反应。共聚焦显微镜用于检查运动终末的结构，PV表达导致运动终末变小，突触小体和活性区减少。这一结果支持了早期的观点，即增加的AP活动通过增加突触前[Ca]促进运动终末生长。
