The Subcellular Distribution of Calcium in the Visual Cells of Crayfish, Observed with the Combined Oxalate-Pyroantimonate Technique, Depends on Extracellular Calcium

1. With the combined oxalate-pyroantimonate method we determined the subcellular distribution of calcium in the photoreceptor cells of the crayfish Orconectes limosus. 2. The calcium antimonate deposits were identified with the electron microscope. Energydispersion X -ray analysis verified that the electron dense deposits contained calcium and antimony. 3. Calcium antimonate deposits were found in the submicrovillar cisternae, mitochondria, multivesicular bodies, and pigment granules, as well as in the cytoplasm . 4. The calcium deposits in the cytoplasm of the retinula cell and in the pigment granules were reduced after incubation of the retinae in a solution with a lowered calcium concentration and even more after we permeabilized the plasma membrane with the saponin β-escin. 5. We suppose that the calcium -storing pigment granules participate in the regulation of the cytosolic calcium concentration of the crayfish photoreceptor cells.

Ca2+-sequestering smooth endoplasmic reticulum in an invertebrate photoreceptor. I. Intracellular topography as revealed by OsFeCN staining and in situ Ca accumulation.

Two ultrastructural approaches were used in photoreceptor cells of the leech, Hirudo medicinalis, to (a) investigate the intracellular topography of the smooth endoplasmic reticulum (SER) and (b) identify among the various subregions of the SER those which might function as Ca-sequestering sites. When the cells are prefixed with CaCl2-containing glutaraldehyde and postfixed with osmium tetroxide-ferricyanide (OsFeCN), only a part of the total SER is specifically stained. The stained SER cisternae include the submicrovillar cisternae (SMC), subsurface cisternae (SSC), the nuclear envelope, Golgi-associated SER, paracrystalline SER, and SER associated with glycogen areas. An extensive tubular SER cisternal system always remains unstained. When the cells are permeabilized by saponin and subsequently incubated with Ca2+, MgATP, and oxalate, the SMC (Walz, 1979, Eur. J. Cell Biol. 20:83-91), the SSC and the nuclear envelope contain electron-opaque Ca-oxalate precipitates indicating their ability to function as an effective Ca2+ sink. The results show that the very elaborate SER in this photoreceptor cell includes many functionally heterogeneous subregions. Of special physiological significance are those components (SMC and SSC) which are effective in Ca2+-buffering in the immediate vicinity of the plasma membrane.