title: Penicillin-induced triphasic modulation of GABAA receptor-operated chloride current in frog sensory neuron.
abstract: Effects of penicillin-G (PCN) on GABA-evoked Cl- current (IGABA) were investigated in freshly dissociated frog sensory neurons by the use of the concentration-clamp technique combined with the suction-pipette method. Under conditions where the internal and external solutions allowed only Cl- permeability, PCN elicited triphasic modulation on IGABA, consisting of two modes of blockade on IGABA and a following rebound (rebound-like transient IGABA). Simultaneously applied PCN and GABA depressed IGABA immediately (phasic blockade), with the depressed IGABA slightly recovering in amplitude to achieve a stable level of blockade (tonic blockade). When a solution containing a mixture or PCN and GABA was quickly replaced by one containing GABA alone, a rebound-like transient Cl- current (IR) was evoked. Each component of the PCN actions on IGABA was PCN- and GABA-concentration-dependent. The reversal potential for each component of the PCN actions on IGABA was close to the chloride equilibrium potential (ECl) calculated using the Nernst equation. The current-voltage (I-V) relations for both the phasic and tonic blockade revealed inward rectification, while I-V curves for the control IGABA and the IR were outwardly rectified. The degree of IGABA-desensitization and the amplitude of the IR correlated well. The data suggest that partial removal of the GABAA receptor-desensitization may result in generation of the IR.
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D007700:Kinetics; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D010400:Penicillin G / Q000494:pharmacology*; D011892:Rana catesbeiana; D011963:Receptors, GABA-A / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D002712:Chlorides; D007473:Ion Channels; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D010400:Penicillin G