PHOTORECEPTOR CELLS DISSOCIATED FROM THE COMPOUND LATERAL EYE OF THE HORSESHOE-CRAB, LIMULUS-POLYPHEMUS .2. FUNCTION

A combination of enzymatic digestions and mechanical disruption was us ed to isolate photoreceptor cells from the compound lateral eye of the horseshoe crab, Limulus polyphemus. The cells were maintained in a cu lture medium and tested for function using whole-cell and cell-attache d patch configurations of the gigaseal technique. The cells dissociate d from the eye generated spontaneous voltage and current bumps in the dark, and depolarized in a graded fashion to increasing intensities of light over several decades, producing responses similar to those of c ells in vivo. Currents evoked during voltage clamp were similar to tho se in ventral photoreceptor cells of Limulus, although transient curre nts in the dark- and light-activated currents were smaller in isolated latera! eye cells, perhaps because of the slow speed and spatial nonu niformity of the clamp in these large cells. In addition to isolated c ells, dissociation of the compound eye produced small clusters of cell s and isolated ommatidia which were also tested for function. Comparis on of the electrical characteristics of isolated cel', with those of c ells in small clusters and in their ommatidial matrix suggests that th e electrical junctions normally connecting photoreceptor cells within an ommatidium are functional in the latter groups, but not in isolated cells. Cell-attached patches of rhabdomeral membrane of isolated cell s contained light-activated channels, resembling those observed in ven tral photoreceptor cells, but no voltage-activated channels. Similar p atches of arhabdomeral membrane contained voltage-activated channels, but no light-activated channels. We conclude that this preparation is suitable for studies of processes involved in generating the light res ponse in invertebrate photoreceptor cells.