Functional properties of spontaneous IPSCs and glycine receptors in rod amacrine (AII) cells in the rat retina

Abstract

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 τfast ∼ 4.8 ms (97.5% amplitude contribution) and τslow ∼ 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 τfast ∼ 4.6 ms (85% amplitude contribution) and τslow ∼ 17 ms. Double-pulse experiments indicated recovery from desensitization after a 100-ms pulse of glycine with a double-exponential time course (τfast ∼ 71 ms and τslow ∼ 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 α1β heteromeric receptors with a contribution from α1 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. © 2006 The Authors. Journal compilation © 2006 The Physiological Society.