Spread of the light response along the rod outer segment: an estimate from patch-clamp recordings

Longitudinal spread of the light response was studied using cell-attached patch-clamp recordings from the outer segments of isolated rod photoreceptors from toad retina. The effective photon-collecting area over which photoisomerizations influenced the membrane current through the recorded patch of membrane was determined by measuring the probability of a detectable response as a function of flash photon density (i.e. a "frequency-of-seeing" experiment). The effective collecting area averaged 0.40 micron2, which corresponds to a total sampling length of approximately 1 micron for the patch electrode.