Electrophysiological properties of mouse horizontal cell

Acknowledgements: We thank Susanne Wallenstein for excellent technical assistance, Ulrike Janssen-Bienhold for assistance with the PCR, and Jennifer Shelley for reading and improving the manuscript. 517). 2 GABA-induced currents have been characterized in isolated horizontal cells from lower vertebrates, but not in mammalian horizontal cells. Therefore, horizontal cells were isolated after enzymatical and mechanical dissociation of the adult mouse retina and visually identified. We recorded from horizontal cell bodies using the whole-cell and outside-out configuration of the patch-clamp technique. Extracellular application of GABA induced inward currents carried by chloride ions. GABA-evoked currents were completely and reversibly blocked by the competitive GABA A receptor antagonist bicuculline (IC 50 = 1.7 µM), indicating expression of GABA A but not GABA C receptors. Their affinity for GABA was moderate (EC 50 = 30 µM), and the Hill coefficient was 1.3, corresponding to two GABA binding sites. GABA responses were partially reduced by picrotoxinin with differential effects on peak and steady-state current values. Zinc blocked the GABA response with an IC 50 value of 7.3 µM in a non-competitive manner. Furthermore, GABA receptors of horizontal cells were modulated by extracellular application of diazepam, zolpidem, DMCM, pentobarbital, and alphaxalone, thus showing typical pharmacological properties of CNS GABA A receptors. GABA-evoked single-channel currents were characterized by a main conductance state of 29.8 pS and two subconductance states (20.2 pS and 10.8 pS, respectively). Kinetic analysis of single-channel events within bursts revealed similar mean open times and closed times for the main conductance and the 20.2-pS subconductance state, resulting in open probabilities of 44.6% and 42.7%, respectively. The ratio of open to closed times, however, was significantly different for the 10.8-pS subconductance state with an open probability of 57.2%.