Figure 1. Paired recordings from rod bipolar and AII amacrine cells reveal a transient and sustained component of the postsynaptic response to voltage steps.

A, left, image of a RBC and AII amacrine cell pair visualized by injection of Alexa 488 through the recording pipettes. Middle, family of AII amacrine EPSCs evoked by a series of voltage steps in a presynaptic RBC. Duration of the steps was 50 ms. Series was from −49 mV to −34 mV in 3 mV increments. Inset, averaged spontaneous EPSC obtained from the same cell. Right, summary of the AII response as a function of presynaptic voltage (n= 9 cells). B, depolarizing 100 ms step in a RBC elicited a sustained Ca²⁺ current in the RBC and a transient EPSC in the AII amacrine. C, comparison of the kinetics of the response to a voltage step that was half-maximal (in this pair, a step to −37 mV) and maximal (−31 mV). Response to a step to −19 mV is also shown. Each trace is the average of 3–5 responses. Inset, Normalization of the half-maximal and maximal responses reveals a similarity of the kinetics of the fast component. D, left, AII responses from one cell to 10, 20 and 30 ms voltage steps of 20 mV in the presence of 100 μm PTX, 50 μm TPMPA and 10 μm strychnine. Inset, corresponding RBC calcium currents recorded during the 20 ms (top) and 30 ms steps. Middle, responses to 15, 25 and 35 ms (20 mV) voltage steps in the presence of bath applied Hepes (20 mm), bicarbonate (20 mm) and TBOA (75 μm). Inset, corresponding RBC calcium currents from the 20 ms (top) and 30 ms steps. Note that the superimposed outward current, which can be observed in the control traces to the left, is blocked by Hepes and TBOA. Right, responses from an AII cell to 20 mV steps of 10, 15 and 20 ms duration in the absence (black, thin line) and presence (blue in the online version, thick line) of cyclothiazide. The peaks of the responses have been scaled in all three panels. E, single raw traces showing the response in an AII cell to a 20 mV step in an RBC immediately after break in (black, thin line) and after 5 min of recording (blue in the online version, thick line) with an internal solution containing 6 mm BAPTA. Normal internal solution was used for the AII recording (see Methods).