Ca2+ stores in Purkinje neurons: endoplasmic reticulum subcompartments demonstrated by the heterogeneous distribution of the InsP3 receptor, Ca(2+)-ATPase, and calsequestrin

Abstract

The nature of second messenger-responsive intracellular Ca2+ stores in neurons remains open for discussion. Here, we demonstrate the existence in Purkinje cells (PCs) of endoplastic reticulum (ER) subcompartments characterized by an uneven distribution of three proteins involved in Ca2+ storage and release: the inositol 1,4,5-trisphosphate (InsP3) receptor, Ca(2+)-ATPase, and calsequestrin. Ca(2+)-ATPase and the InsP3 receptor have a widespread, although not identical, distribution throughout the ER. Calsequestrin is localized throughout the smooth ER and is particularly concentrated in pleiomorphic vesicles with a moderately electron-dense core, which appear to represent a subcompartment of the smooth ER. In double-labeling experiments many of these vesicles were unlabeled by InsP3 receptor antibodies. These results suggest a key role of the ER as an intracellular Ca2+ store and demonstrate a possible structural basis for distinct intracellular Ca2+ pools regulated by different second messengers.

Light and Electron Microscopic Localization of Presenilin-1 in Primate Brain

“…In dendritic spines, these structures generally had the appearance of smooth tubular membranes or vesicles (Fig. 8 A,B), which morphologically resemble a dendritic SER subcompartment that has been described previously (Satoh et al, 1990;Takei et al, 1992). Labeling in presynaptic elements was seen less frequently, but PS1 immunoreactivity was seen occasionally on the cytoplasmic surfaces of some vesicles (Fig.…”

“…It is possible that PS1 may be present on a very small subpopulation of synaptic vesicles. Alternatively, the labeled membranes may represent nonsynaptic vesicle components of the presynaptic terminal, such as elements of the SER network, which is known to extend into distal axons and terminals (Takei et al, 1992;Terasaki et al, 1994;Krijnse-Locker et al, 1995). Taken as a whole, these ultrastructural observations in monkey brain suggest a localization of PS1 to a subcompartment of the SER in both cell bodies and processes.…”

“…Most PS1 immunoreactivity in the neuropil is seen within dendritic spines on smooth tubulovesicular profiles. The morphological appearance of these organelles and their characteristic localization in dendritic spines suggests that they are components of the SER network (Satoh et al, 1990;Takei et al, 1992). The SER in neurons has been characterized as an intricate communicating network that extends from the cell body into the terminal segments of dendritic and axonal processes (Broadwell and Cataldo, 1984;Terasaki et al, 1994).…”

Endoplasmic reticulum: a dynamic patchwork of specialized subregions.

“…In oocytes, neurons, smooth muscle, and various secretory cells, a RyR-based Ca" release system, analogous therefore to the SR, has been shown to coexist with the Ca" release system activated by inositol 1,4,5-trisphosphate (IP3), which is thought to be ubiquitous. In some cell types, the IP3 receptor (IP3R) and RyRmediated responses could be triggered independently, and exhaustion of one response left the other apparently unaffected (reviewed Petersen and Wakui, 1990 Takei et al, 1992). Evidence for distinct localization of IP3R and RyR in subsets of these vacuoles was also reported (Volpe et al, 1991).…”

“…Stacks of smooth-surfaced cisternae (crystalloid ER), in direct luminal continuity with the rest of the ER, have been characterized molecularly in UT-1 cells grown in high concentrations of lovastatin, an inhibitor of the 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase (Pathak et al, 1986) and in Purkinje neurons of the cerebellum (Satoh et al, 1990;Takei et al, 1992). In either case, cistemal stacks apparently result from the accumulation of an overexpressed ER membrane protein: the HMG-CoA reductase and IP3R, respectively.…”