Localization of calcium in nerve fibers

Abstract

Using the desheathed nerve preparation, a pyroantimonate precipitation method was used to examine the distribution of electron-dense particles seen in various organelles of the nerve fibers following exposure of nerve to various levels of Ca2+ in vitro. The presence of Ca2+ in the electron-dense particles was indicated by their extraction with EGTA and by the use of energy-dispersive X-ray microanalysis. In normal Ringer or in a Ca2+ -free medium, electron-dense particles were seen associated with the outer membrane of the mitochondria, with the smooth endoplasmic reticulum (SER), along the axolemma and yet others scattered throughout the axoplasm. When nerves were incubated in media containing higher than normal concentrations of 20-60 mM Ca2+, an increase in the number of such electron-dense particles was seen in the axoplasm and within the mitochondrial matrix. Nerves loaded with a high concentration of 60mM Ca2+ could be depleted of these particles after transfer to a Ca2+ -free or low Ca2+ Ringer medium. The sequestration of Ca2+ in axonal organelles is discussed with respect to Ca2+-regulatory mechanisms in the axon needed to maintain a low level of Ca2+ which is optimal for the support of axoplasmic transport.

Changes in intra‐axonal calcium distribution following nerve crush

“…The addition of calcium during fixation for electron microscopy creates electron dense precipitate, apparently at specific calcium binding sites in the cell (Oschman and Wall, 1972;Hillman and Llinas, 1974). Other investigators have used oxalate or pyroantimonate after calcium loading in vitro to demonstrate sites of binding or sequestration of exogenous calcium (Henkart et al, 1978;Chan et al, 1984). Pyroantimonate precipitates endogenous calcium, and by adding pyroantimonate to the primary fixative others have defined precipitates bound to membrane as well as distribute through the cytoplasm in a number of cell types (Duce and Keen, 1978).…”

The correlation between calcium absorption and electrophysiological recovery in crushed rat peripheral nerves

“…8,9 High levels of calcium precipitate localization were observed after Wallarian degeneration of the nerve.…”

“…For the data analysis, there were four time points (2,8,12, and 24 weeks) with six animals for each time point (n 5 24). For each animal, four different nerve samples were taken: (1) proximal to and (2) distal to the crushed segment, (3) the crushed segment itself, and (4) a sham control mid-segment.…”

Uptake and Distribution of ⁴⁵Ca in the Brain of Chronically Uremic Rats

“…A number of studies in a variety of tissues [8][9][10] including brain [26] have shown that from 50 to 90% of total tissue calcium may be bound to extracellular ligands, making it quite likely that alterations in the measured calcium content of tissues merely reflect changes in the calcium bound extracellulary. On the other hand, between 30 and 65% of the intracellular calcium is located in the mitochondria [8,11,12], and the mitochondria are thought to be the primary buffers for excess intracellular calcium, particu larly in situations of abnormal calcium loads [12,18]. Consequently, the uptake of 45Ca by brain mitochondria was examined in orderto obtain a more direct assessment of intracellular calcium.…”

“…Cytosolic Ca2+ is normally maintained at 10 6A/by a variety of membraneassociated systems including that of the mitochondria [8]. I nasmuch as mitochondria contain the largest proportion of intracellular calcium [8,11,12] and are thought to participate in the regulation of intracellular calcium by buffering excess calcium that enters the cell [13][14][15][16][17][18], it was suggested that intracellular calcium may not be increased in uremia and that the previously reported results might be due to increases in extracellularly bound calcium. We recently reported that the calcium content of brain mito chondria is not increased in chronically uremic rats [7].…”