The Journal of Neurophysiology Vol. 87 No. 4 April 2002, pp. 1694-1702
Copyright ©2002 by the American Physiological Society

Na⁺/Ca²⁺ Exchanger in GABAergic Presynaptic Boutons of Rat Central Neurons

Cellular and System Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan

Doi, Atsushi, Yasuhiro Kakazu, and Norio Akaike. Na⁺/Ca²⁺ Exchanger in GABAergic Presynaptic Boutons of Rat Central Neurons. J. Neurophysiol. 87: 1694-1702, 2002. Rat Meynert neurons were acutely isolated using a dissociation technique that maintains functional GABAergic presynaptic boutons. Miniature inhibitory postsynaptic currents (mIPSCs) were recorded under voltage-clamp conditions using whole cell patch-clamp recordings. Using the frequency of mIPSCs as a measure of presynaptic terminal excitability, the existence of a Na⁺/Ca²⁺ exchanger (NCX) in these GABAergic nerve terminals was clearly demonstrated. Both the frequency and the amplitude of mIPSCs were unaffected by replacement of extracellular Na²⁺. However, in this Na⁺-free external solution, ouabain could now induce a transient increase of mIPSCs frequency, which was not inhibited by adding Cd²⁺ or cyclopiazonic acid but was inhibited by removing external Ca²⁺. This indicates that this transient potentiation was dependent on external Ca²⁺, but that this Ca²⁺ influx was not via voltage-dependent Ca²⁺ channels. KB-R7943, an inhibitor of NCX, at a concentration of 3 × 10⁶ M, reduced this transient increase of mIPSCs frequency without affecting mIPSCs amplitude and the response to exogenous GABA. These results demonstrate the existence of NCX in these GABAergic nerve terminals. In zero external Na⁺, ouabain causes an accumulation of intraterminal Na⁺ and a resultant influx of Ca²⁺ through the reversed mode operation of NCX. However, under more physiological conditions, NCX may also operate in a forward mode and serve to maintain low intracellular [Ca²⁺] in nerve terminals.