GABAA and GABAC Receptors on Hybrid Bass Retinal Bipolar Cells. Qian, Haohua, John E. Dowling. Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138 and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543.
APStracts 2:0199N, 1995.
SUMMARY AND CONCLUSIONS
GABA responses from solitory hybrid bass retinal bipolar cells were studied using conventional and perforated whole-cell patch clamp recording. GABA elicited a chloride current in bipolar cells which had both transient and sustained components. The transient component was sensitive to bicuculline and resembled GABAA mediated currents, whereas the more sustained component was resistant to bicuculline and resembled the responses mediated by GABAC receptors. The bicuculline-resistant GABA responses recorded from the bipolar cells could not be modulated by either diazepam or pentobarbital, and they were unaffected by phaclofen and 2-hydroxysaclofen, GABAB receptor antagonists. On the other hand, the bicuculline-resistant GABA responses could be blocked substantially by I4AA (imidazole-4-acetic acid), a competitive antagonist of GABAC receptors. Noise analysis of the GABA elicited currents suggested a different single channel conductance for GABAA (10.1 pS) and GABAC receptors (3.6 pS). Zinc, a putative modulator of synaptic transmission, strongly inhibited the GABAC responses on bipolar cells, whereas the GABAA responses were not significantly affected by zinc. The proportion of the GABAC to GABAA responses varied widely between bipolar cells. Local application of GABA onto dendrites or axon terminals showed that both types of GABA receptors are present on both regions of the cell. The distinct properties of these two GABA receptor types suggest that they play different roles in retinal function. 

Received 30 March 1995; accepted in final form 19 June 1995.
APS Manuscript Number J212-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.