AJP - Cell Physiology, Vol 246, Issue 3 259-C265, Copyright © 1984 by American Physiological Society
Internal perfusion studies demonstrating GABA-induced chloride responses in frog primary afferent neurons
K. Hattori, N. Akaike, Y. Oomura and S. Kuraoka
Cl- current in gamma-aminobutyric acid (GABA)-sensitive neurons of the frog
dorsal root ganglia was separated from other ionic components (i.e., Na+,
Ca2+, and K+ currents) using a suction pipette technique, which allowed
internal perfusion and current clamp. The GABA-induced depolarization
response increased slightly on substituting Na+ by
tris(hydroxymethyl)amino-methane+ or Ca2+ by Mg2+ in the external solution.
Additional replacement of external and internal K+ with Cs+ further
enhanced the GABA response. The GABA response was virtually unaffected when
the internal perfusate contained, in addition to 60 mM Cl-, large organic
anions such as isethionate-, aspartate-, and citrate- (each 70 mM) as well
as aspartate- and GABA (each 35 mM). The reversal potential of GABA-induced
Cl- response (EGABA) was equal to Cl- equilibrium potential (ECl) and
behaved as a simple Cl- electrode following changes of external and
internal Cl- concentrations. These observations indicate the adequacy of
internal perfusion. The GABA-induced Cl- response increased in a sigmoidal
dose-dependent manner, in which the threshold GABA concentration was around
10(-7) M and the GABA response reached ECl at 10(-4) M. When GABA
concentration was higher than 6 X 10(-6) M, the responses were always
accompanied by a rapid desensitization.
