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¹ University of Bergen, Department of Biomedicine, Bergen, Norway

AII amacrine cells play a crucial role in retinal signal transmission under scotopic conditions. We have used rat retinal slices to investigate the functional properties of inhibitory glycine receptors on AII cells by recording spontaneous IPSCs (spIPSCs) in whole cells and glycine-evoked responses in outside-out patches. Glycinergic spIPSCs displayed fast kinetics with an average 10–90% rise time of 500 µs, and a decay phase best fitted by a double-exponential function with _fast 4.8 ms (97.5% amplitude contribution) and _slow 33 ms. Decay kinetics were voltage dependent. Ultrafast application of brief (2–5 ms) pulses of glycine (3 mM) to patches, evoked responses with fast deactivation kinetics best fitted with a double-exponential function with _fast 4.6 ms (85% amplitude contribution) and _slow 17 ms. Double-pulse experiments indicated recovery from desensitization after a 100-ms pulse of glycine with a double-exponential time course (_fast 71 ms and _slow 1713 ms). Non-stationary noise analysis of spIPSCs and patch responses, and directly observed channel gating yielded similar single-channel conductances (41 to 47 pS). In addition, single-channel gating occurred at 83 pS. These results suggest that the fast glycinergic spIPSCs in AII cells are probably mediated by 1ß heteromeric receptors with a contribution from 1 homomeric receptors. We hypothesize that glycinergic synaptic input may target the arboreal dendrites of AII cells, and could serve to shunt excitatory input from rod bipolar cells and transiently uncouple the transcellular current through electrical synapses between AII cells and between AII cells and ON-cone bipolar cells.

(Received 3 May 2006; accepted after revision 4 July 2006; first published online 7 July 2006)
Corresponding author E. Hartveit: University of Bergen, Department of Biomedicine, Jonas Lies vei 91, N-5009 Bergen, Norway. Email: espen.hartveit{at}biomed.uib.no

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