Yarowsky P J, Carpenter D O
Brain Res. 1978 Apr 7;144(1):75-94. doi: 10.1016/0006-8993(78)90436-5.
Aplysia neurons show 5 different types of response (three excitatory and two inhibitory) to iontophoretic application of gamma-aminobutyric acid (GABA). Four of these are associated with a membrane conductance increase, but one is associated with a conductance decrease. The most common response is a fast hyperpolarization which reverses at about--58 mV and is sensitive to manipulation of external Cl- concentration, and thus is due to a specific increase in Cl- conductance. There is an infrequent, slower hyperpolarizing response which does not reverse above about--80 mV and is insensitive to external Cl-. This response appears to result from a conductance increase to K+. Two types of depolarizing responses are associated with conductance increases. These responses differ in their latency, duration and sensitivity to curare. The more frequent is relatively rapid (peak at 1-2 sec) and is depressed by curare at high concentrations. In other neurons, GABA causes a slower response, peaking at 6-10 sec, which is not curare-sensitive. Usually for both types of response, the voltage and conductance changes are completely abolished by perfusion with Na+-free seawater, and the responses cannot be reversed with depolarization. In other neurons such as L11, the response can be reversed with depolarization, and appears to result from a conductance increase to both Na+ and Cl-. In neuron R15, GABA causes a slow depolarizing response (peak at about 9 sec) which is associated with a decreased membrane conductance, probably to K+. The classical GABA antagonists, picrotoxin and bicuculline, block Cl- responses but no others, while the fast Na+ and Cl- responses are depressed by curare. Strychnine does not affect any GABA response. The multiplicity of GABA responses, the specificity of their organization and the fact that only some neurons have receptors for GABA, argue that GABA may have a role as a neurotransmitter in Aplysia. Furthermore, the existence of several types of excitatory GABA response suggests that GABA may function both as an inhibitory and excitatory neurotransmitter.
海兔神经元对离子电泳施加的γ-氨基丁酸（GABA）表现出5种不同类型的反应（三种兴奋性反应和两种抑制性反应）。其中四种反应与膜电导增加有关，但有一种反应与电导降低有关。最常见的反应是快速超极化，在约-58 mV时反转，并且对外部Cl-浓度的变化敏感，因此是由于Cl-电导的特异性增加所致。有一种不常见的、较慢的超极化反应，在约-80 mV以上不会反转，并且对外部Cl-不敏感。这种反应似乎是由于对K+的电导增加所致。两种去极化反应都与电导增加有关。这些反应在潜伏期、持续时间和对箭毒的敏感性方面有所不同。较常见的反应相对较快（在1-2秒达到峰值），在高浓度箭毒作用下会受到抑制。在其他神经元中，GABA会引起较慢的反应，在6-10秒达到峰值，对箭毒不敏感。通常对于这两种类型的反应，通过用无Na+海水灌注，电压和电导变化会完全消失，并且反应不能通过去极化逆转。在其他神经元如L11中，反应可以通过去极化逆转，并且似乎是由于对Na+和Cl-的电导增加所致。在神经元R15中，GABA会引起缓慢的去极化反应（在约9秒达到峰值），这与膜电导降低有关，可能是对K+的电导降低。经典的GABA拮抗剂，印防己毒素和荷包牡丹碱，会阻断Cl-反应但不影响其他反应，而快速的Na+和Cl-反应会受到箭毒的抑制。士的宁不影响任何GABA反应。GABA反应的多样性、其组织的特异性以及只有一些神经元具有GABA受体这一事实表明，GABA可能在海兔中作为一种神经递质发挥作用。此外，几种类型的兴奋性GABA反应的存在表明，GABA可能既作为抑制性神经递质又作为兴奋性神经递质发挥作用。
