AJP - Cell Physiology, Vol 258, Issue 3 C452-C460, Copyright © 1990 by American Physiological Society
Augmentation of GABA-induced current in frog sensory neurons by pentobarbital
N. Akaike, N. Tokutomi and Y. Ikemoto
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
The effect of pentobarbital sodium (PB) on the gamma-aminobutyric acid
(GABA)-induced macroscopic and microscopic Cl- currents (ICl and iCl,
respectively) was studied in the soma membrane of isolated frog sensory
neurons using a rapid concentration-jump and patch-clamp technique. The
GABA-induced ICl was composed of a transient peak and a steady plateau. PB
shifted the concentration-response curve of the GABA-induced peak ICl to
the left without affecting the maximum value. The apparent dissociation
constant (KD) decreased from 13 microM at control to 8.0, 4.8, and 2.9
microM by adding 10, 30, and 100 microM PB, respectively. PB also shifted
the concentration-response curve for the plateau ICl to the left and
augmented the maximum value of the plateau, indicating an increase in the
available receptor-channel complex. The Hill coefficient (n = 2) in
concentration-response curves of both peak and plateau responses was not
changed by adding PB. Both the activation and desensitization phases of
GABA-induced ICl consisted of two exponential components. PB significantly
increased the time constant of slow desensitization component at all
concentrations of GABA used. In the "inside-out" configuration, PB markedly
increased the open probability (Po) of a GABA-gated single Cl- channel
having a conductance of 14.57 +/- 2.3 pS (n = 123) without affecting the
single-channel conductance. The increase of Po was due to the prolongation
of mean open time (tau of the tau os) and shortening of mean closed time
(tau cf and tau cs), resulting in the increase of channel-opening
events.(ABSTRACT TRUNCATED AT 250 WORDS)
