Heat shock protein 70 in the retina of Xenopus laevis, in vivo and in vitro: effect of metabolic stress

Abstract.

We utilized the frog eyecup as an in vitro model to compare heat-shock protein 70 (hsp70) synthesis in untreated retinas and in hyperthermia-, arsenite-, or glutamate-treated retinas. Hsp70-like immunoreactivity in vivo was concentrated in the photoreceptors in a pattern that was basically unchanged throughout the light/dark cycle. Retinas from eyecups in culture displayed the same immunoreactivity pattern as those in vivo except for a rapid, transient increase in immunoreactivity surrounding the photoreceptor nuclei. The immunoreactivity pattern in heat-treated retinas was similar to that of controls, but overall intensity was greatest in the outer plexiform layer. Arsenite-treated retinas displayed hsp70-like immunoreactivity in a pattern that was also like that of control retinas. Glutamate exposure resulted in increased hsp70-like immunoreactivity not only in the inner segments and outer plexiform layer, but also in photoreceptor nuclei. Gel fluorography of ³⁵S-methionine-labeled proteins from heat- and arsenite-stressed retinas demonstrated increased synthesis of one or two proteins of ∼70 kD and one protein of ∼90 kD. Exposure of eyecups to glutamate did not result in detectable changes in protein synthesis. Following exposure to heat or glutamate, the retinas displayed swelling of the inner plexiform layer (IPL) as well as pyknotic nuclei in the inner nuclear layer. Exposure of eyecups to arsenite caused clumping of the melanin granules of the retinal pigmented epithelium (RPE) but not IPL swelling or pyknotic nuclei. We have shown that the stress response can be manipulated successfully in the in vitro Xenopus retina and that the pattern of the response depends on the nature of the stressor.