Search PubMed⌕ Search

Biomedical subjects

P Volpe

Publications and source records attributed to P Volpe.

At least 109 records · Page 6Linked to original sources
PubMed1989

Sequence homology of a canine brain calcium-binding protein with calregulin and the human Ro/SS-A antigen.

A 60 kDa calcium-binding protein (CBP) was purified from canine brain and its N-terminal sequence determined to be: Glu-Pro-Ala-Ile-Tyr-Phe-Lys-Glu-Gln-Phe-Leu-Asp-Gly-Asp-Gly-X-Thr-Arg-X- Ile- Glu-Ser-Lys. This sequence is very similar to that of "Ccalregulin", a CBP of unknown function which is similar in size and appears to be present in most animal tissues. An unexpected and even more striking similarity was found with the N-terminal sequence of the human Ro/SS-A antigen, a 60 kDa protein which has long been implicated in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus. These findings suggest that the Ro/SS-A antigen is probably also a CBP.

Amino Acid Sequence↗
PubMed1989

Antibodies to junctional sarcoplasmic reticulum proteins: probes for the Ca2+-release channel.

The junctional face membrane plays a key role in excitation-contraction coupling in skeletal muscle. A protein of 350 kDa, tentatively identified as a component of the junctional feet, connects transverse tubules to terminal cisternae of sarcoplasmic reticulum [Kawamoto, Brunschwig, Kim & Caswell (1986) J. Cell Biol. 103, 1405-1414]. The membrane topology and protein composition of sarcoplasmic reticulum Ca2+-release channels of rabbit skeletal muscle were investigated using an immunological approach, with anti-(junctional face membrane) and anti-(350 kDa protein) polyclonal antibodies. Upon preincubation of the terminal cisternae with anti-(junctional face membrane) antibodies, Ca2+-ATPase and Ca2+-loading activities were not affected, whereas anti-(350 kDa protein) antibodies stimulated Ca2+-ATPase activity by 25% and inhibited Ca2+-loading activity by 50% (at an antibody/terminal cisternae protein ratio of 1:1). Specific photolabelling of terminal cisternae proteins with [14C]doxorubicin was prevented by both anti-(junctional face membrane) and anti-(350 kDa protein) antibodies. Stimulation of Ca2+ release by doxorubicin was prevented by both anti-(junctional face membrane) and anti-(350 kDa protein) antibodies. Half-maximal inhibition was obtained at an antibody/terminal cisternae protein ratio of 1:1. Kinetic measurements of Ca2+ release indicated that anti-(350 kDa protein) antibodies prevented Ca2+-induced Ca2+ release, whereas the ATP-stimulation and the inhibition by Mg2+ were not affected. These results suggest that: (i) Ca2+- and doxorubicin-induced Ca2+ release is mediated by Ca2+ channels which are selectively localized in the junctional face membrane; (ii) the 350 kDa protein is a component of the Ca2+-release channel in native terminal cisternae vesicles; and (iii) the Ca2+-activating site of the channel is separate from other allosteric sites.

Animals↗
PubMed1989

The unraveling architecture of the junctional sarcoplasmic reticulum.

The sarcoplasmic reticulum (SR) of skeletal muscle controls the contraction-relaxation cycle by raising and lowering the myoplasmic free-Ca2+ concentration. The coupling between excitation, i.e., depolarization of sarcolemma and transverse tubule (TT) and Ca2+ release from the terminal cisternae (TC) of SR takes place at the triad. The triad junction is formed by a specialized region of the TC, the junctional SR, and the TT. The molecular architecture and protein composition of the junctional SR are under active investigation. Since the junctional SR plays a central role in excitation-contraction coupling and Ca2+ release, some of its protein constituents are directly involved in these processes. The biochemical evidence supporting this contention is reviewed in this article.

Animals↗
PubMed1989

Distribution of endoplasmic reticulum and calciosome markers in membrane fractions isolated from different regions of the canine brain.

Four regions of the canine brain (frontal lobe, parieto-occipital lobe, brainstem, and cerebellum) were each fractionated by differential centrifugation into a crude mitochondrial pellet (P2) and a crude microsomal pellet (P3). Markers of endoplasmic reticulum (glucose-6-phosphate phosphatase and rotenone-insensitive NADPH cytochrome c reductase) and markers of the 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store ([3H]IP3 binding and IP3-induced Ca2+ release) were measured. No correlation was found between the two classes of markers, which suggests that the IP3 receptor does not belong to the endoplasmic reticulum in canine brain. Cerebellum P2 and P3 fractions displayed levels of [3H]IP3 binding 10- to 30-fold higher, and rates of IP3-induced Ca2+ release greater than 15-fold faster than the homologous cerebrum and brainstem fractions. Actively accumulated Ca2+ was only partially released by IP3, both before and after saponin disruption of the plasma membrane compartment. The proportion of the IP3-sensitive Ca2+ store relative to that of the total (IP3-sensitive and IP3-insensitive) Ca2+ store was variable; i.e., it was larger in cerebellum P2 (approximately 90%) than in cerebrum fractions (less than 30%). Cerebellum fractions constitute the best source from which an IP3-sensitive Ca2+ storing organelle can be purified.

Animals↗
PubMed1989

Calciosome, a sarcoplasmic reticulum-like organelle involved in intracellular Ca2+-handling by non-muscle cells: studies in human neutrophils and HL-60 cells.

Calciosomes are intracellular organelles in HL-60 cells, neutrophils and various other cell types, characterized by their content of a Ca2+-binding protein that is biochemically and immunologically similar to calsequestrin (CS) from muscle cells. In subcellular fractionation studies the CS-like protein copurifies with functional markers of the inositol 1,4,5-trisphosphate (IP3) releasable Ca2+-store. These markers (ATP-dependent Ca2+-uptake and IP3-induced Ca2+-release) show a subcellular distribution which is clearly distinct from the endoplasmic reticulum and other organelles. In morphological studies, antibodies against rabbit skeletal muscle CS protein specifically stained hitherto unrecognized vesicles with a diameter between 50 and 250 nm. Thus both, biochemical and morphological studies indicate that the calsequestrin containing intracellular Ca2+-store, now referred to as the calciosome, is distinct from other known organelles such as endoplasmic reticulum. Calciosomes are likely to play an important role in intracellular Ca2+-homeostasis. They are possibly the intracellular target of inositol 1,4,5-trisphosphate and thus the source of Ca2+ that is redistributed into the cytosol following surface receptor activation in non-muscle cells.

Biological Transport, Active↗
PubMed1989

Terminal cisternae of denervated rabbit skeletal muscle: alterations of functional properties of Ca2+ release channels.

Terminal cisternae (TC) of skeletal muscle represent the specialized compartment from which Ca2+ is released into the myoplasm after a propagated action potential. In this study we have investigated the morphology, protein composition, and Ca2+ release properties of TC isolated from rabbit gastrocnemius muscle 2 wk after nerve sectioning. Thin-section electron microscopy showed that TC vesicles from denervated muscle were enriched in calsequestrin (CS) and contained a larger fraction of the junctional sarcoplasmic reticulum (SR), as judged by membrane profiles with morphologically intact feet structures. Accordingly, the yield of junctional SR from denervated muscle was twice that of control muscle, and the protein pattern of TC vesicles exhibited an increase in junctional protein components, e.g., CS and the 350-kDa protein. The larger content of the 350-kDa protein, or ryanodine receptor (F.A. Lai, H. Erickson, E. Rousseau, Q.-Y. Liu, and G. Meissner, Nature Lond. 331: 315-319, 1988; T. Imagawa, J. S. Smith, R. Coronado, and K. P. Campbell. J. Biol. Chem. 262: 10636-10643, 1987; L. Hymel, M. Inui, S. Fleischer, and H. Schindler, Proc. Natl. Acad. Sci. USA 85:441-445, 1988) was paralleled by an increased binding site density (Bmax) for ryanodine binding in denervated muscle TC. The effects of ruthenium red, a Ca2+ release blocker, on Ca2+ loading rate and Ca2+-ATPase activity suggested that TC from denervated muscle were less permeable to Ca2+. After active Ca2+ loading, both doxorubicin and caffeine induced Ca2+ release from isolated TC, yet Ca2+ release rates were reduced in denervated muscle TC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1989

Direct inhibition of inositol-1,4,5-trisphosphate-induced Ca2+ release from brain microsomes by K+ channel blockers.

Tetraethylammonium and 9-tetraethylammonium have previously been reported to inhibit inositol-1,4,5-trisphosphate (IP3)-induced Ca2+ release from brain microsomes, purportedly by blocking potassium channels [Biochem. J. 258:617-620 (1988)]. The effects of these and other K+ channel blockers have been studied here in greater detail using a spectrophotometric assay for Ca2+ movements into and out of canine brain microsomes. IP3-induced Ca2+ release was inhibited by substitution of K+ in the medium with nominally impermeant cations or by addition of most of the K+ channel blockers tested. Nevertheless, addition of valinomycin to the medium (to provide an alternative pathway for counter-ion K+ movements) failed to alleviate the inhibition of IP3-induced Ca2+ release caused by K+ channel blockers. To determine whether these substances act by inhibition of IP3 binding or by direct interaction with the Ca2+ channel of the internal store that promotes IP3-induced Ca2+ release, their effect on [3H]IP3 binding was investigated. None of the K+ channel blockers tested inhibited [3H]IP3 binding. Nearly all the K+ channel blockers appear to interact directly with a Ca2+ channel of the intracellular stores or perhaps interfere with its coupling to the IP3 receptor. Because of their multiplicity of actions, these substances cannot be presumed to be either selective K+ channel blockers or selective inhibitors of IP3-induced Ca2+ release from internal stores. Three of them were even found to partially inhibit valinomycin-stimulated 86Rb uptake into liposomes.

4-Aminopyridine↗
PubMed1989

Pharmacologic differentiation between inositol-1,4,5-trisphosphate-induced Ca2+ release and Ca2+- or caffeine-induced Ca2+ release from intracellular membrane systems.

Various known Ca2+ channel blockers and intracellular Ca2+ antagonists have been tested for effects of inositol-1,4,5-trisphosphate (IP3)-induced Ca2+ release from isolated canine brain microsomes. In agreement with previous reports, heparin, p-chloromercuribenzoic acid, W-7, cinnarizine, flunarizine, certain local anesthetics, La3+, and Ca2+ inhibit the release of Ca2+ induced by addition of IP3. In addition, we report here pronounced inhibition of IP3-induced Ca2+ release by low levels of Cd2+, by relatively high concentrations of TMB-8, and by phytic acid. In contrast, a number of blockers of other Ca2+ channels (nifedipine, verapamil, dantrolene, dithiothreitol, and ruthenium red) have relatively little or no effect on IP3-induced Ca2+ release from brain microsomes. The relative ineffectiveness of substances that inhibit Ca2+- or caffeine-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum suggests that release of Ca2+ from caffeine- and IP3-sensitive neuronal Ca2+ stores is likely to be mediated by different channels. Further evidence that different channels are involved is presented by way of demonstration of the lack of Ca2+-induced Ca2+ release from these brain microsomes and the lack of effect on sarcoplasmic reticulum caffeine-induced Ca2+ release of certain inhibitors of IP3-induced Ca2+ release used here. Among IP3-induced Ca2+ release blockers, La3+ appeared to be exceptional in its ability to stimulate microsomal Ca2+ uptake sufficiently to attenuate release of Ca2+ induced by IP3. Most blockers of IP3-induced Ca2+ release appear not to function by way of inhibiting K+ counter-ion movements (valinomycin does not reverse the inhibition) but rather by way of direct interaction with the IP3 receptor or the Ca2+ channel that mediates the IP3-induced Ca2+ release. Inhibition of [3H]IP3 binding to the microsomes by phytic acid, heparin, pyrophosphate, p-chloromercuribenzoic acid, and Ca2+ could be demonstrated but not by the other substances tested.

Animals↗
PubMed1988

D-myo-inositol 1,4,5-trisphosphate phosphatase in skeletal muscle.

The presence and subcellular distribution of D-myo-inositol 1,4,5-trisphosphate phosphatase (InsP3ase) in rabbit fast-twitch skeletal muscle were investigated. A specific InsP3ase was found in both sarcotubular-membrane and soluble fractions. Membrane-bound InsP3ase accounted for 60-65% of total activity. The InsP3ase was detected both on the surface membranes and on the InsP3-sensitive intracellular Ca2+ store, i.e. the sarcoplasmic reticulum. The Km for inositol 1,4,5-trisphosphate (InsP3) ranged between 15 and 18 microM, and the highest Vmax. (19.6 nmol of InsP3 hydrolysed/min per mg of protein) was measured in a membrane fraction enriched in transverse tubules. Several known inhibitors of InsP3ase, e.g. 2,3-bisphosphoglycerate, CdCl2 and EDTA, were active on skeletal-muscle InsP3ase. Total InsP3ase activity of both rabbit and frog skeletal muscle was comparable with that of rabbit brain, liver and main pulmonary artery (smooth muscle). The present results are consistent with the hypothesis that InsP3 plays a role in excitation-contraction coupling in skeletal muscle [Volpe, Salviati, Di Virgilio & Pozzan (1985) Nature (London) 316, 347-349].

Animals↗
PubMed1988

Isolation of terminal cisternae of frog skeletal muscle. Calcium storage and release properties.

Sarcoplasmic reticulum (SR) terminal cisternae (TC) of frog (Rana esculenta) fast-twitch skeletal muscle have been purified by isopycnic sucrose density gradient centrifugation. Biochemical characteristics and Ca2+ release properties have been investigated and compared to those of the homologous fraction of rabbit skeletal muscle TC. The frog SR fraction obtained at the 38/45% sucrose interface appears to be derived from the terminal cisternae region as judged by: (a) thin section electron microscopy showing vesicles containing electron opaque material and squarelike (feet) projections at the outer surface; (b) protein composition (Ca2+-ATPase, calsequestrin, and high Mr proteins); (c) Ca2+ fluxes properties. The content of calsequestrin was higher in frog TC by 50% and the Ca2+ binding capacity (624 or 45 nmol of Ca2+/mg of TC protein, depending upon experimental conditions) was 3-4 times that of rabbit TC. Species-specific antigenic differences were found between junctional SR proteins of frog and rabbit TC. After active Ca2+ preloading in the presence of pyrophosphate (Palade, P. (1987) J. Biol. Chem. 262, 6135-6141), caffeine and doxorubicin elicited Ca2+ release from either TC fraction but with much faster rates in frog TC than in rabbit TC (14 versus 3 mumol of Ca2+/min/mg of protein). The present results provide new evidence for the existence of marked differences in Ca2+ release properties between TC of amphibian and mammalian fast-twitch muscle. Higher Ca2+ binding capacity and faster release rates in frog TC might compensate for the comparably greater diffusion distance being covered by the released Ca2+ from the Z-line to the actomyosin cross-bridges in the A-I overlap region.

Animals↗
PubMed1988

Denervation-induced proliferative changes of triads in rabbit skeletal muscle.

Protein compositional and functional differences exist between longitudinal and junctional sarcoplasmic reticulum (SR) in relation to Ca transport and to Ca release. In light of this knowledge, we have reinvestigated the effects of denervation on SR of rabbit gastrocnemius, a predominantly fast muscle. Electron microscopy of 2-weeks denervated muscle showed proliferation of transverse tubules (TT), forming junctional contacts with SR terminal cisternae (TC). At coincident periods, the yield of muscle microsomes was increased, and their fractionation by sucrose-density centrifugation demonstrated a relative increase of heavy vesicles. Thin-section electron microscopy of heavy SR from denervated muscle showed an increased number of vesicles containing calsequestrin (CS) as compared with control muscle. Electrophoretic analysis confirmed the relative decrease of Ca-ATPase protein and the striking increase of CS both in total microsomes and in heavy SR vesicles. Calcium loading and Ca-ATPase activity as well as the density of Ca-ATPase protein were decreased to a similar extent (20-30%) in denervated muscle microsomes. Stimulation of Ca-ATPase activity by Ca-ionophore A23187 showed that the vesicles were tightly sealed. When probed by competitive ELISA with antibody to SR Ca-ATPase from pure fast muscle, the Ca-ATPase of denervated microsomes was found to be highly cross reactive. Cleveland's peptide maps of the Ca-ATPase protein after partial digestion with S. aureus V8 protease also showed no significant change after denervation. Changes in cholesterol content and in the ratio of Mg-ATPase to Ca-ATPase activity of denervated muscle microsomes indicated a 4-fold increase of TT protein, i.e., from about 3% to not more than 12% of total protein, at 2 weeks after denervation. All these changes were totally reversed upon reinnervation of muscle fibers, and the consequent muscle recovery, as obtained by nerve crushing instead of nerve sectioning. From these results, we conclude that denervated adult fast muscle, similarly to immature fast muscle, contains more junctional SR. However, the molecular and catalytic properties of the Ca-ATPase are unaffected by denervation.

Animals↗
PubMed1988

Calcium binding proteins of junctional sarcoplasmic reticulum: detection by 45Ca ligand overlay.

In skeletal muscle, the junctional sarcoplasmic reticulum (JFM) plays a crucial role in excitation-contraction coupling and Ca2+ release. In the present report, the sarcoplasmic reticulum (SR) was fractionated into longitudinal SR (LSR), terminal cisternae (TC), and JFM. Each fraction had a unique protein profile as detected by SDS-polyacrylamide gel electrophoresis as well as specific Ca2+ binding proteins as judged by 45Ca ligand overlay of nitrocellulose blots. Ca2+ binding proteins of LSR were the Ca2+ ATPase (Mr of 115K), an 80K polypeptide, and the intrinsic glycoprotein (Mr of 160K); Ca2+ binding proteins of JFM were polypeptides with the following Mr values: 350K and 325K (feet components), 200K, 170K, a doublet of 140K, 118K, 65K (calsequestrin), and 52K. Measurements of Ca2+ binding to SR fractions by equilibrium dialysis indicated that 8-17 nmol Ca2+/mg of protein was specifically bound. After EDTA extraction of calsequestrin, JFM still bound Ca2+ (5-6 nmol/mg of protein), suggesting the existence of specific Ca2+ binding sites. The Ca2+ binding sites of Ca2+-gated Ca2+ release channels might be on two JFM polypeptides (Mr's of 350K and 170K) which are putative channel constituents (F. Zorzato, A. Margreth, and P. Volpe (1986) J. Biol. Chem. 261, 13252-13257).

Animals↗
PubMed1988

"Calciosome," a cytoplasmic organelle: the inositol 1,4,5-trisphosphate-sensitive Ca2+ store of nonmuscle cells?

Calsequestrin (CS) is the protein responsible for the high-capacity, moderate affinity binding of Ca2+ within the terminal cisternae of the sarcoplasmic reticulum, believed up to now to be specific for striated muscle. The cells of two nonmuscle lines (HL-60 and PC12) and of two rat tissues (liver and pancreas) are shown here to express a protein that resembles CS in many respects (apparent mass and pH-dependent migration in NaDodSO4/PAGE; blue staining with StainsAll dye; Ca2+ binding ability) and is specifically recognized by affinity-purified antibodies against skeletal muscle CS. In these cells, the CS-like protein is shown by immunofluorescence and immunogold procedures to be localized within peculiar, heretofore unrecognized structures distributed throughout the cytoplasm. These structures appear to be discrete organelles, which we propose to be named "calciosomes." By cell fractionation (Percoll gradient and free-flow electrophoresis), the CS-like protein of HL-60 cells is shown to copurify with the markers of the inositol 1,4,5-trisphosphate (Ins-P3)-sensitive Ca2+ store, whereas the markers of other organelles (endoplasmic reticulum, Golgi complex, mitochondria, endosomes) and of the plasma membrane do not. Calciosome might thus be the intracellular target of Ins-P3--i.e., the source of the Ca2+ redistributed to the cytosol following receptor-triggered generation of the messenger.

Animals↗
PubMed1988

Immunocytochemistry of calciosomes in liver and pancreas.

Calciosomes are small cytoplasmic vacuoles identified in various nonmuscle cell types by their content of protein(s) similar to calsequestrin (CS), the Ca2+ storage protein of the muscle sarcoplasmic reticulum (SR). These entities have been interpreted as the "primitive" counterpart of the SR, and suggested to be the organelle target of inositol-1,4,5-triphosphate action (Volpe, P., K. H. Krause, S. Hashimoto, F. Zorzato, T. Pozzan, J. Meldolesi, and D. P. Lew. Proc. Natl. Acad. Sci. USA. 85:1091-1095). Immunoperoxidase and immunogold experiments carried out in both thick and ultrathin cryosections of rat hepatocytes and pancreatic acinar cells by using antimuscle CS antibodies revealed a specific labeling widely distributed in the entire cytoplasm, while nuclei were negative. Individual calciosomes appeared as small (105 nm) membrane-bound vacuoles intermingled with, and often apposed to ER cisternae and mitochondria. Other calciosomes were scattered in the Golgi area, in between zymogen granules and beneath the plasma membrane. The cumulative volume of the CS-positive organelles was measured to account for the 0.8 and 0.45% of the cytoplasm in liver and pancreas cells, respectively. The real total volume of the calciosome compartment is expected to be approximately twice as large. In hepatocytes, structures similar to CS-positive calciosomes were decorated by antibodies against the Ca2+ ATPase of muscle SR, while ER cisternae were not. By dual labeling, colocalization was revealed in 53.6% of the organelles, with 37.6% positive for the ATPase only. CS appeared preferentially confined to the content, and the Ca2+ ATPase to the contour of the organelle. The results suggested a partial segregation of the two antigens, reminiscent of their well-known segregation in muscle SR. Additional dual-label experiments demonstrated that hepatic calciosomes express neither two ER markers (cytochrome-P450 and NADH-cytochrome b5 reductase) nor the endolysosome marker, luminal acidity (revealed by 3-[2,4-dinitroanilino]-3'-amino-N-methyl dipropylamine). Calciosomes appear as unique cytological entities, ideally equipped to play a role in the rapid-scale control of the cytosolic-free Ca2+ in nonmuscle cells.

Animals↗
PubMed1988

Ca2+ release from sarcoplasmic reticulum of skinned fast- and slow-twitch muscle fibers.

We have performed a comparative study of Ca2+ release from the sarcoplasmic reticulum (SR) of chemically skinned fibers from rabbit fast- and slow-twitch skeletal muscle. Ca2+ fluxes have been indirectly monitored by following either tension development or the inhibition of net Ca2+-loading rate by a light-scattering method. Several drugs (Ca2+-release modulators) have been used to either trigger or block Ca2+ release. Our results indicate that caffeine, doxorubicin, and ryanodine activate Ca2+ release, whereas ruthenium red blocks Ca2+ release from both fast- and slow-twitch skinned fibers. Caffeine has greater affinity for slow SR, whereas doxorubicin, ruthenium red, and ryanodine have greater affinity for fast SR. Our results indicate that Ca2+-release mechanisms in fast and slow SR are homologous but not identical and that differences in twitch-contraction time might be also related to the inherent properties of the Ca2+-release mechanism.

Animals↗
PubMed1988

The Ins(1,4,5)P3-sensitive Ca2+ store of non-muscle cells: endoplasmic reticulum or calciosomes?

The binding of a number of extracellular ligands (hormones, growth factors, neurotransmitters etc.) to their plasma membrane receptors causes hydrolysis of phosphatidylinositol bisphosphate to initiate the formation of two second messengers, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and diacylglycerol, DAG. DAG has been shown to activate protein kinase C, whereas Ins(1,4,5)P3 induces the release of Ca2+ from an intracellular pool. This rapidly mobilizable, Ins(1,4,5)P3-sensitive Ca2+ store has until now been identified as the endoplasmic reticulum, ER. We demonstrate that this is untenable and provide evidence for the existence of an unrecognized organelle, the 'calciosome'. This conclusion is based on the following experimental evidence. (1) There is no correlation between the abundance of ER and the amount Ins(1,4,5)P3-sensitive Ca2+ release. (2) There is no correlation between ER markers and those for the Ca2+ store [Ins(1,4,5)P3 binding and sensitivity, Ca2+ uptake]. (3) A protein similar to striated muscle calsequestrin, CS, has been identified in microsomal fractions from a number of tissues; it copurifies with markers of the Ca2+ store, but not with those of ER. (4) Subcellular localization of the CS-like protein by electron microscopy reveals that in all cells so far analysed this protein is localized in small, membrane-enclosed structures, calciosomes, which are also stained by an anti-Ca2+-ATPase antibody. Calciosomes appear to be morphologically distinct from any other known cell organelle. (5) Although they stain different portions of the calciosomes (membrane and lumen, respectively), anti-Ca2+-ATPase and anti-CS antibodies do not recognize any antigen in ER cysternae; antibodies directed against known components of ER do not bind to calciosomes.

Animals↗
PubMed1988

Immunocytological identification of the microsomal calcium store of nonmuscle cells.

The biochemical and functional similarities between skeletal muscle sarcoplasmic reticulum and the microsomal Ca2+ store of nonmuscle cells are discussed. It is shown that antibodies raised against two characteristic proteins of sarcoplasmic reticulum, Ca2+ ATPase and calsequestrin, recognize similar proteins in nonmuscle cells. The subcellular distribution of these two antigens was studied at the subcellular levels in ultrathin cryosections. In a variety of cell types these two proteins were found to be localized in small membrane enclosed vesicles, apparently distinct from other known organelles. We propose that these newly recognized structures (calciosomes) represent the functional equivalent of sarcoplasmic reticulum in nonmuscle cells.

Animals↗