Calcium content and distribution in egg vesicles of Galleria mellonella (Lepidoptera) as determined by X-ray microanalysis

Ultrastructural distribution of Ca++ within neurons. An oxalate pyroantimonate study

We used the oxalate-pyroantimonate technique to determine the ultrastructural distribution of Ca++ in neurons of the rat sciatic nerve. The content of the precipitate was confirmed by X-ray microanalysis and appropriate controls. In the cell bodies of the dorsal root ganglia, Ca++ precipitate was found in the Golgi, mitochondria, multivesicular bodies and large vesicles of the cytoplasm but not in lysosomes, and was prominently absent from regions of rough endoplasmic reticulum and ribosomes. It was seen in the nucleus but not in the nuclear bodies or nucleolus. Within the axon itself, Ca++ precipitate was also found sequestered in mitochondria and smooth endoplasmic reticulum. In addition Ca++ precipitate found diffusely throughout the axoplasm exhibited a discrete and heterogeneous distribution. In myelinated fibers the amount of precipitate decreased predictably in the axoplasm beneath the Schmidt-Lanterman cleft and in the paranodal regions at the nodes of Ranvier. This correlated with the presence of dense precipitate in the Schmidt-Lanterman cleft themselves and in the paranodal loops of myelin. Intracytoplasmic ionic Ca++ is maintained at 10(-7) M by balanced processes of influx, sequestration and extrusion. The irregular distribution of Ca++ precipitate in the axoplasm of myelinated fibers suggests that there may be specific regions of preferential efflux across the axolemma.

Ultracytochemical localization and microprobe quantitation of calcium stores in the insect oocyte

Detection of calcium in the follicles of Galleria mellonella (Lepidoptera) was performed using two cytochemical methods. Calcium precipitation was obtained either with ammonium oxalate (AO) or with N,N-naphtaloylhydroxylamine (NHA). In both cases the X-ray "on line" analysis monitored the presence of calcium in the oocytes, which was correlated with the accumulation of yolk spheres. Concentration of calcium in oocytes filled with yolk and treated with AO amounted to 9 mmoles per 1,000 g tissue wet weight. This value is similar to that calculated previously for follicles untreated with any reagent and prepared for the analysis by the freeze-drying technique (Przeļecka et al. 1980). Examination of the ultrastructure of oocytes treated with NHA revealed calcium precipitate at the follicular epithelium/oocyte interface, in endocytotic canaliculi and vesicles formed by the oocyte plasma membrane, in ooplasm, and in yolk spheres. In oocytes treated with AO, the calcium-precipitate intermingled with the precipitate produced by the osmium alone. The presumed cause of this phenomenon is discussed.