The effects of monensin and of puromycin on transport of membrane components in the frog retinal photoreceptor. II. Electron microscopic autoradiography of proteins and glycerolipids.
Monensin converts the Golgi apparatus of rod photoreceptors into distended vacuoles, similar to those seen in other monensin-treated cell types, and leads to the accumulation of [3H]leucine in the distended vacuoles. As evaluated by quantitative, electron microscopic autoradiography, transport of newly made proteins--both to the outer segments and to the presynaptic terminals--is inhibited. These effects suggest that the Golgi apparatus is involved in transport in both principal directions within the highly polarized photoreceptors, a matter of interest since there seems to be only a single, extensive, Golgi apparatus in the cell body. Seemingly there are two distinguishable "sorting" routes, for proteins, out of the Golgi apparatus and, for the terminals, an additional non-Golgi route. Accumulation of newly made glycerolipids in the outer segments and terminals is less affected by monensin than is accumulation of new proteins, and glycerolipid accumulation is little affected by puromycin, an inhibitor of protein synthesis. These latter findings suggest that the routes or mechanisms of assembly of newly made lipids into membranes in the photoreceptors are at least partially dissociable from those for newly made proteins.