Cytochalasin D inhibits l-glutamate-induced disc shedding without altering l-glutamate-induced increase in adhesiveness

Abstract

Excitatory amino acid-stimulated disc shedding is correlated with the appearance of microfilament-rich ensheathing processes of the retinal pigment epithelium (RPE) and increased apparent adhesiveness between photoreceptors and RPE in explanted eyecups of Xenopus laevis. We have compared the time course of disc shedding and increased retinal adherence during l-glutamate treatment. Increased adherence was measured on the basis of the tendency of the apical RPE domains to partition with isolated neural retinas. In medium supplemented with l-glutamate (12 m m) or kainate (100 μ m), a glutamate analog, the time course of increased partitioning of melanin pigment-rich cell fragments which contain ensheathing processes differs, even though the kinetics of induced disc shedding is the same in either case. Co-treatment with cytochalasin D (5 μ m) completely blocks l-glutamate-induced disc shedding, as well as formation of microfilament-rich ensheathing processes, even though it has little effect upon apparent adhesiveness. The virtually complete dissociation of the effects of l-glutamate on disc shedding from that on increased adhesiveness of photoreceptors to RPE suggests that increased retinal adherence and pseudopod formation may be unrelated causally.