Internal perfusion studies demonstrating GABA-induced chloride responses in frog primary afferent neurons.
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.
D000818:Animals; D000838:Anions / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D009475:Neurons, Afferent / Q000378:metabolism*; D010477:Perfusion; D011892:Rana catesbeiana / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D000838:Anions; D002412:Cations; D002712:Chlorides; D005680:gamma-Aminobutyric Acid