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This Article Full Text Full Text (PDF) All Versions of this Article: 577/1/45    most recent jphysiol.2006.119560v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Palmer, M. J. Search for Related Content PubMed PubMed Citation Articles by Palmer, M. J. Related Collections Neuroscience

¹ Neuroscience Group, Institute for Science and Technology in Medicine, Keele University, Keele, ST5 5BG, UK

The transmission of light responses to retinal ganglion cells is regulated by inhibitory input from amacrine cells to bipolar cell (BC) synaptic terminals. GABA_A and GABA_C receptors in BC terminals mediate currents with different kinetics and are likely to have distinct functions in limiting BC output; however, the synaptic properties and localization of the receptors are currently poorly understood. By recording endogenous GABA receptor currents directly from BC terminals in goldfish retinal slices, I show that spontaneous GABA release activates rapid GABA_A receptor miniature inhibitory postsynaptic currents (mIPSCs) (predominant decay time constant (_decay), 1.0 ms) in addition to a tonic GABA_C receptor current. The GABA_C receptor antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) has no effect on the amplitude or kinetics of the rapid GABA_A mIPSCs. In addition, inhibition of the GAT-1 GABA transporter, which strongly regulates GABA_C receptor currents in BC terminals, fails to reveal a GABA_C component in the mIPSCs. These data suggest that GABA_A and GABA_C receptors are highly unlikely to be synaptically colocalized. Using non-stationary noise analysis of the mIPSCs, I estimate that GABA_A receptors in BC terminals have a single-channel conductance () of 17 pS and that an average of just seven receptors mediates a quantal event. From noise analysis of the tonic current, GABA_C receptor is estimated to be 4 pS. Identified GABA_C receptor mIPSCs exhibit a slow decay (_decay, 54 ms) and are mediated by approximately 42 receptors. The distinct properties and localization of synaptic GABA_A and GABA_C receptors in BC terminals are likely to facilitate their specific roles in regulating the transmission of light responses in the retina.

(Received 22 August 2006; accepted after revision 25 September 2006; first published online 28 September 2006)
Corresponding author M. J. Palmer: Huxley Building, School of Life Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK. Email: m.j.palmer{at}cns.keele.ac.uk

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