Inhibition of Transient Potassium Current in Cultured and Acutely- Dissociated Mouse Hippocampal Neurons by GABA A Receptor Activation. Rui-Lin Wu and Michael E. Barish. Division of Neurosciences, Beckman Research Institute of the City of Hope, Duarte, CA 91010.
APStracts 3:0025N, 1996.
1. The regulation of A-current, one of several transient voltage-gated potassium currents, was studied using whole-cell gigaohm seal voltage clamp techniques on hippocampal pyramidal neurons that were either acutely- dissociated from postnatal mouse brain or isolated from embryonic mouse brain and grown in dissociated culture. These neurons also express GABA A receptors, the activation of which can, under some circumstances, depolarize immature neurons and the dendrites of more mature neurons. 2. Application of GABA (50 [mu]M) reduced the amplitude of A-current when potassium current amplitude was measured during a period of slow and incomplete desensitization of I GABA . A- current was reduced to 67 +/- 9% of control (mean +/- s.d., n = 14) in acutely-dissociated neurons, and to 64 +/- 11% of control ( n = 15) in cultured neurons. Similar A-current reductions were seen in large outside-out membrane patches pulled from somata of cultured neurons, an observation suggesting that imperfect control of membrane voltage was not responsible for A-current inhibition. 3. A-current inhibition exhibited the sensitivity expected of a GABA A -sensitive process. It was mimicked by muscimol, and blocked by bicuculline, picrotoxin and reduction of [Cl - ] in the external solution. Baclophen and phaclophen, effective as agonist and antagonist on GABA B receptors, did not affect A-currents or their inhibition. Reduction in extracellular osmolarity (to increase cell swelling as might occur with Cl - entry), or removal of external HCO 3 - (which might flow inward through GABA A channels and cause local external acidification), did not affect A-current or its inhibition. The mechanisms of inhibition is not clear at present. 4. We suggest that reduced A-current may favor GABA-induced depolarization and consequent activation of voltage-gated calcium channels.

Received 4 October 1995; accepted in final form 5 January 1995.
APS Manuscript Number J662-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 January 96