Fig. 4.
L-AP4 increases noise and reduces signal in excitatory currents from the OFF α-cell. A: current evoked by dark flash. The signal R was measured from the average currents in two 40-ms windows (gray rectangles). Noise σR was measured as the standard deviation of R across stimulus trials. B: signal R graphed against contrast was fit with the Naka-Rushton function, R = Rmaxcn+z/(cn + c50n) + K, where c is contrast; and c50, n, and z are fitted parameters. Note that both axes are log scale: thus above 1% contrast, L-AP4 reduces signal by about twofold. C: noise σR graphed against contrast was fit with the square root of the Naka-Rushton function. Noise is approximately equal to its value at zero contrast up to and including 2% contrast in control and 8% contrast in L-AP4 (dashed lines). L-AP4 reduced noise at low contrasts, but not at moderate contrasts.