Light intensity dependence of the Islow. (A) Islows evoked in a cell stimulated with 100-ms flashes of increasing intensity, as indicated by the attenuation factor on the right. (B) Intensity series for the photocurrent in a different photoreceptor displayed at a faster time scale. The amplitude of the response reaches saturation at a stimulus intensity below the threshold for the slow current. (C) Plot of the peak amplitude of the photocurrent (open symbols) and that of the slow aftercurrent (filled symbols) averaged for three cells in each condition. Error bar indicates SEM. (D) The slow current is also elicited with more modest stimulus intensities, provided that their duration is extended. The panel shows the response to a step of light attenuated by −1.8 log but maintained for the duration of the recording. Holding potential of −50 mV in all panels, unattenuated light intensity of 19 × 1015 photons × cm−2 × s−1.
