Hyperlipidemia is induced in regucalcin transgenic rats with increasing age

Regucalcin plays an important role as a regulatory protein in intracellular signaling pathway in many cells. Regucalcin transgenic (TG) rats have been shown to induce a remarkable increase in serum triglyceride and HDL-cholesterol concentrations at the age of 36 weeks (35). Furthermore, this was investigated in regucalcin TG rats with increasing age (14, 25, 36 or 50 weeks). Serum triglyceride or HDL-cholesterol concentration was markedly increased in regucalcin TG male and female rats at 14, 25, 36 or 50 weeks of age. Serum-free fatty acid concentration was significantly elevated in regucalcin TG male and female rats at 25, 36 or 50 weeks. In the TG female rats, a significant increase in serum free fatty acid concentration was also observed at 14 weeks of age, while it was not seen in the TG male rats. Serum-free cholesterol concentration was significantly increased in regucalcin TG female rats at 14, 25, 36 or 50 weeks. Such an increase was not induced in the TG male rats. Moreover, serum calcium concentration was significantly raised in regucalcin TG male and female rats at 50 weeks of age. Also, serum albumin concentration was significantly elevated in regucalcin TG female rats at 25, 36, or 50 weeks of age. Such an increase was not observed in the TG male rats. Serum zinc, glucose or urea nitrogen concentration was not significantly altered in TG male and female rats. This study demonstrates that hyperlipidemia is uniquely induced in regucalcin TG rats with increasing age.     

Change in lipid components in the adipose and liver tissues of regucalcin transgenic rats with increasing age: suppression of leptin and adiponectin gene expression

Regucalcin plays a multifunctional role as a regulatory protein in intracellular signaling pathway in many cell types. Regucalcin transgenic (TG) rats have been shown to experience hyperlipidemia with increasing age. This study was undertaken to determine whether lipid components in the adipose and liver tissues are changed in regucalcin TG rats in vivo. Female regucalcin TG rats were used at 7 or 50 weeks of age. Serum triglyceride or HDL-cholesterol concentrations were significantly increased in 7-week-old regucalcin TG rats as compared with those in 7-week-old normal rats. Serum triglyceride, total cholesterol, HDL-cholesterol, or free fatty acid concentrations were significantly increased in 50-week-old regucalcin TG rats. Meanwhile, triglyceride content in the adipose tissues was significantly increased in 50-week-old regucalcin TG rats,while the free fatty acid content was not significantly changed. Triglyceride, total cholesterol, or free fatty acid content in the liver tissues was significantly decreased in 50-week-old regucalcin TG rats. Liver glycogen content was significantly decreased in 7- or 50-week-old regucalcin TG rats. In addition, regucalcin mRNA and its protein levels were seen in the adipose tissues of normal rats. Those levels were not significantly changed in regucalcin TG rats at 50 weeks of age. Leptin mRNA expression in the adipose or liver tissues was significantly decreased in 50-week-old regucalcin TG rats. Adiponectin mRNA levels were not significantly changed in the adipose tissues of 50-week-old regucalcin TG rats, while the levels were significantly decreased in the liver tissues. This study demonstrates that the disorder of lipid metabolism in the adipose and liver tissues is induced in regucalcin TG rats with aging, and that the gene expression of leptin or adiponectin is suppressed in TG rats.     

Osteoclastogenic potential of bone marrow cells increases with age in elderly women with fracture

The most reliable explanation for decreasing bone mass in elderly women is an imbalance of osteoclastic resorption and osteoblastic formation resulting from a relative increase in osteoclastic resorption. However, it is not clear whether an increase in osteoclastic bone resorption with age is due to increased osteoclast formation or to osteoclastic bone resorption activity. In this study, using a human bone marrow culture system, we attempt to clarify the increase in osteoclast formation with age. The mononuclear cell-rich fraction from bone marrow, obtained from the proximal region of the femur from female elderly patients with fracture, were cultured for 14 days in the presence of 1,25 dihydroxyvitamin D(3). Tartrate-resistant acid phosphatase-positive multinucleated cells were counted as osteoclasts. In our investigation, human osteoclast formation in the bone marrow culture increased with age in elderly women (age 64-96 years). The osteoclast formation was positively correlated with macrophage-colony stimulation factor and prostaglandin E(2) production in bone marrow culture. Also, osteoclast formation ex vivo was negatively correlated with bone mineral density of the lumbar spine (L2-L4). The above results indicate that the osteoclastogenic potential of bone marrow cells increases with aging in elderly women with fracture, and suggest that a decrease in bone mass of elderly women may be due to an increase in osteoclast population associated with aging.     

Role of endogenous regucalcin in transgenic rats: suppression of protein tyrosine phosphatase and ribonucleic acid synthesis activities in liver nucleus

The role of endogenous regucalcin, a regulatory protein of Ca2+ signaling, in the regulation of liver nuclear function was investigated by using regucalcin transgenic (TG) rats. Regucalcin levels were significantly increased in the liver nuclei of regucalcin TG male and female rats. Nuclear protein tyrosine phosphatase activity was significantly elevated in the presence of anti-regucalcin monoclonal antibody (50 ng/ml) in the reaction mixture containing liver nuclear protein obtained from normal (wt) rats. This increase was significantly prevented in the liver nuclei of regucalcin TG rats. Moreover, nuclear ribonucleic acid (RNA) synthesis was significantly suppressed in the liver nuclei of regucalcin TG rats as compared with that of normal rats. The effect of calcium chloride (10 micro M) or anti-regucalcin monoclonal antibody (50 ng/ml) in increasing RNA synthesis was completely blocked in the liver nuclei of the TG rats. These results suggest that endogenous regucalcin plays a suppressive role in the regulation of liver nuclear function in rats.     

Role of endogenous regucalcin in brain function: suppression of cytosolic nitric oxide synthase and nuclear protein tyrosine phosphatase activities in brain tissue of transgenic rats

The role of regucalcin, a regulatory protein of Ca2+ signaling, in the regulation of brain function was investigated by using regucalcin transgenic (TG) rats. Western blot analysis showed a remarkable expression of regucalcin protein in the cytosol and nucleus of the brain tissue of TG female rats (5-week-old) as compared with that of wild-type (wt) female rats. In TG male rats, the enhancement of regucalcin expression in the brain cytosol and nucleus was only slight. Nitric oxide (NO) synthase activity was significantly decreased in the brain cytosol of TG female rats. Protein tyrosine phosphatase activity was not significantly altered in the brain nucleus of TG female rats. The presence of calcium chloride (10 microM) or anti-regucalcin monoclonal antibody (50 ng/ml) in the enzyme reaction mixture caused a significant increase in cytosolic NO synthase and nuclear protein tyrosine phosphatase activities in the brain tissue of wt rats. The increase was significantly prevented in the brain cytosol and nucleus of TG rats. The present study supports the view that endogenous regucalcin plays a suppressive role in the regulation of brain function in rats.     

Hypercalcemia in dogs with lymphosarcoma. Biochemical, ultrastructural, and histomorphometric investigations

Dogs with lymphosarcoma and hypercalcemia had decreased trabecular bone volume and increased osteoclastic osteolysis, whereas dogs with lymphosarcoma that were normocalcemic did not have increased bone resorption. Increased osteoclastic resorption was present only in bone from hypercalcemic dogs that contained neoplastic tissue but not in bone free of tumors, suggesting that the factor(s) responsible for stimulating bone resorption were elaborated locally by the tumor tissue. Hypercalcemic dogs with lymphosarcoma had decreased concentrations of plasma immunoreactive parathyroid hormone and serum 1,25-(OH)2D compared with normocalcemic dogs with lymphosarcoma and control dogs with and without other neoplasms. Immunoreactive parathyroid hormone was not detected in lymphosarcoma tissue. The plasma concentration of 13,14-dihydro-15-keto-prostaglandin E2 (PGE2M) was increased approximately 2-fold in hypercalcemic dogs with lymphosarcoma as compared with other groups. Urine excretion of calcium, phosphorus, and hydroxyproline were increased in hypercalcemic dogs with lymphosarcoma. Ultrastructurally, lymphosarcomas were composed of tumor cells with large nuclei and a paucity of cytoplasmic organelles. Light and electron microscopic examination of parathyroid glands revealed inactive or atrophic chief cells in dogs with lymphosarcoma and hypercalcemia. The increased osteoclastic bone resorption in hypercalcemic dogs with lymphosarcoma was not mediated by increased circulating levels of immunoreactive parathyroid hormone and 1,25-(OH)2D but was dependent upon infiltration of bone marrow by neoplastic cells and, presumably, the local production of a bone resorption-stimulating factor.     

Suppressive effect of regucalcin on protein phosphatase activity in the heart cytosol of normal and regucalcin transgenic rats

The role of regucalcin, a regulatory protein in intracellular signaling pathway, in the regulation of protein phosphatase activity in the heart muscle cytosol was investigated by using normal (wild-type) and regucalcin transgenic (TG) rats. Protein phosphatase activity was assayed in a reaction mixture containing the cytosolic protein in the presence of phosphotyrosine, phosphoserine, and phosphothreonine. The addition of calcium chloride (10 and 20 microM) in the enzyme reaction mixture caused a significant increase in protein phosphatase activity toward three phosphoaminoacids. Trifluoperazine (10 and 20 microM), an antagonist of calmodulin, completely inhibited calcium (10 microM) addition-increased protein phosphatase activity toward three phosphoaminoacids. Moreover, the calcium (10 microM)-increased enzyme activity toward phosphoserine and phosphothreonine was significantly enhanced by the addition of calmodulin (2.5 or 5 microg/ml). Such an enhancement was not seen in the presence of phosphotyrosine. Regucalcin (10(-9) and 10(-8) M) significantly inhibited protein phosphatase activity toward three phosphoaminoacids in the presence of ethylene glycol bis (2-aminoethlether) N,N,N',N'-tetraacetic acid (EGTA; 1 mM), without Ca2+ addition. The inhibitory effect of regucalcin (10(-10)-10(-8) M) was also seen in the presence of calcium chloride (10 microM). Western blot analysis showed a remarkable expression of regucalcin protein in the cytosol of heart of regucalcin TG female rats as compared with that of wild-type female rats. Protein phosphatase activity toward three phosphoaminoacids was significantly decreased in the heart cytosol of TG rats. The enhancing effect of calcium (10 microM) addition on protein phosphatase activity toward three phosphoaminoacids was not seen in the heart cytosol of TG rats. This study demonstrates that endogenous regucalcin plays a suppressive role in the regulation of protein phosphatase activity in rat heart cytoplasm.     

Suppressive effect of endogenous regucalcin on protein tyrosine phosphatase activity in the nucleus of rat brain: attenuation with increasing age

The effect of endogenous regucalcin, which is a regulatory protein of Ca2+ signaling, on protein tyrosine phosphatase activity in the nucleus of brain tissues of young and aged rats was investigated. Phosphotyrosine was used as the substrate for assay of protein tyrosine phosphatase activity. Protein tyrosine phosphatase activity in the brain nucleus of young (5 weeks old) rats was significantly increased in the presence of calcium chloride (5-50 micro M) in the enzyme reaction mixture. The increase was completely blocked by the addition of trifluoperazine (10-50 micro M), an antagonist of calmodulin, indicating that the enzyme is activated by endogenous Ca2+/ calmodulin. The addition of regucalcin (10(-4)-10(-8) M) in the enzyme reaction mixture caused a significant decrease in protein tyrosine phosphatase activity in the absence or presence of calcium chloride (20 micro M). Brain nuclear protein tyrosine phosphatase activity was significantly raised in the presence of anti-regucalcin monoclonal antibody (10-50 ng/ml) in the enzyme reaction mixture. The increase was completely prevented by the addition of regucalcin (10(-6) M). In the brain nucleus of aged (50 weeks old) rats, protein tyrosine phosphatase activity was elevated significantly as compared with that of 5 weeks old rats. The effect of anti-regucalcin monoclonal antibody in increasing the enzyme activity in the brain nucleus of aged rats was seen in the presence of 50 ng/ml of the antibody. Such an effect was not found by the antibody of 10 and 25 ng/ml. Regucalcin protein in brain nucleus was detected by Western blot analysis. This level was significantly decreased by increasing age. The present study demonstrates that endogenous regucalcin plays a suppressive role in the regulation of protein tyrosine phosphatase activity in the nucleus of rat brain, and that this regulation is attenuated with increasing age.     

The effect of interleukin-6 and soluble interleukin-6 receptor protein on the bone resorptive activity of human osteoclasts generated in vitro

The role of interleukin-6 (IL-6) in the regulation of bone resorption is and has not been studied using human tissue in vitro. This study exploits a recently described in vitro model, whereby osteoclasts, defined as cells that resorb bone, can be generated from human bone marrow, and investigated the effect of IL-6 and its soluble receptor on bone resorption, in the presence of 1,25-dihydroxyvitamin D₃[1,25(OH)₂ vitamin D₃]. Human bone marrow was cultured to form a confluent stroma, sedimented onto devitalized bone slices, and recharged with non-adherent bone marrow cells. 1,25(OH)₂ vitamin D₃ increased bone resorption, whereas IL-6 failed to induce a similar stimulatory effect. Both IL-6 at 100 ng/ml and soluble IL-6 receptor protein in the absence of exogenous IL-6 inhibited the stimulatory effect of 1,25(OH)₂ vitamin D₃. Bone resorption was never observed when non-adherent haemopoietic cells were cultured in the absence of stroma but in the presence of IL-6, which indicates that IL-6 cannot replace the stromal factor(s) required for the formation of cells capable of resorbing bone. These results suggest that IL-6 at high concentrations is not a critical cytokine in stimulating osteoclastic bone resorption.     

Regucalcin increases superoxide dismutase activity in the heart cytosol of normal and regucalcin transgenic rats

The effect of regucalcin, a regulatory protein in the intracellular signaling system, on superoxide dismutase (SOD) activity in the heart cytosol of normal rats and regucalcin transgenic (TG) rats was investigated. The addition of regucalcin (10(-10) to 10(-8) M) with a physiologic concentration in the enzyme reaction mixture containing the heart cytosol obtained from normal rats caused a significant increase in SOD activity, indicating that regucalcin directly activates the enzyme. The effect of regucalcin (10(-8) M) in increasing SOD activity was not seen in the presence of dithiothreitol (DTT; 0.1 or 1.0 mM), a protecting reagent for sulfhydryl group, or N-ethylmaleimide (NEM; 0.1 or 1.0 mM), a modifying reagent for sulfhydryl group, in the reaction mixture, indicating that regucalcin does not affect the sulfhydryl group. The addition of zinc sulfate (10(-6) to 10(-4) M) in the reaction mixture did not cause a significant change in SOD activity, while the enzyme activity was markedly decreased in the presence of cupric sulfate (10(-6) to 10(-4) M). The activatory effect of regucalcin (10(-8) M) on SOD was seen in the presence of zinc (10(-4) M), while not observed in the presence of copper (10(-4) M). Moreover, SOD activity was significantly enhanced in the heart cytosol of regucalcin TG rats as compared with that of normal rats. This study demonstrates that regucalcin increases SOD activity in the heart cytosol of rats, and that its effect is not related to the sulfhydryl group of enzymes.     

Studies of the cellular cure for osteopetrosis by transplanted cells: Specificity of the cell type in ia rats

Spleen cells from normal rats are known to cure osteopetrosis in ia littermates within 3 weeks. In this study cell suspensions from liver, thymus, bone marrow, salivary gland, skeletal muscle and brain from normal rats were tested for their ability to cure osteopetrosis in ia littermates whose ability to reject these cells had been suppressed by whole-body irradiation. Cells from liver, thymus and bone marrow cured the disease as effectively as spleen cells from normal littermates. Mutants that received cells from salivary gland, muscle and brain remained osteopetrotic. These data suggest that some cell found in spleen, liver, thymus and bone marrow of 10-day-old normal rats, such as a lymphoid cell or stem cell, can restore hemopoiesis and bone resorption in osteopetrotic (ia) rats.     

葛根素抑制1，25-二羟基维生素D3促破骨细胞骨吸收功能的最佳剂量

背景：近年来国内外学者对葛根素的骨形成研究较多,但对于葛根素抑制1,25-(OH)₂D₃促破骨细胞骨吸收功能尚未见报道。 目的：观察不同浓度葛根素在体外对1,25-(OH)₂D₃促破骨细胞骨吸收功能的抑制作用。 方法：收集3周龄小鼠骨髓细胞并接种到24孔培养板中。实验组培养液为1,25-(OH)₂D₃ +α-MEM完全培养基+不同质量浓度的葛根素,对照组不加葛根素。 结果与结论：不同浓度组葛根素处理的培养体系均诱导出破骨样细胞且形态差异不明显;除100 μg/L葛根素组在第3天时碱性磷酸酶表达显著增高外,各组之间培养液上清中碱性磷酸酶水平无显著性差异(P > 0.05);10 μg/L葛根素组培养液上清Ca2+水平在第3,5,12天时较对照组显著降低(P < 0.05~0.01),50 μg/L葛根素组培养液上清Ca²⁺水平在第12天时较对照组显著降低(P < 0.01),100 μg/L葛根素组培养液上清Ca²⁺水平在所有检测点较10 μg/L葛根素组显著上升(P < 0.05)。提示葛根素最佳抑制剂量在10~50 μg/L之间。     

Acidification of the osteoclastic resorption compartment provides insight into the coupling of bone formation to bone resorption

Patients with defective osteoclastic acidification have increased numbers of osteoclasts, with decreased resorption, but bone formation that remains unchanged. We demonstrate that osteoclast survival is increased when acidification is impaired, and that impairment of acidification results in inhibition of bone resorption without inhibition of bone formation. We investigated the role of acidification in human osteoclastic resorption and life span in vitro using inhibitors of chloride channels (NS5818/NS3696), the proton pump (bafilomycin) and cathepsin K. We found that bafilomycin and NS5818 dose dependently inhibited acidification of the osteoclastic resorption compartment and bone resorption. Inhibition of bone resorption by inhibition of acidification, but not cathepsin K inhibition, augmented osteoclast survival, which resulted in a 150 to 300% increase in osteoclasts compared to controls. We investigated the effect of inhibition of osteoclastic acidification in vivo by using the rat ovariectomy model with twice daily oral dosing of NS3696 at 50 mg/kg for 6 weeks. We observed a 60% decrease in resorption (DPYR), increased tartrate-resistant acid phosphatase levels, and no effect on bone formation evaluated by osteocalcin. We speculate that attenuated acidification inhibits dissolution of the inorganic phase of bone and results in an increased number of nonresorbing osteoclasts that are responsible for the coupling to normal bone formation. Thus, we suggest that acidification is essential for normal bone remodeling and that attenuated acidification leads to uncoupling with decreased bone resorption and unaffected bone formation.     

CELLS OF THE MONONUCLEAR PHAGOCYTE SERIES DIFFERENTIATE INTO OSTEOCLASTIC LACUNAR BONE RESORBING CELLS

Although the osteoclast shares several features with other cells of the mononuclear phagocyte system (MPS), its precise cellular ontogeny is unknown, and its membership of the MPS is controversial. This study examined whether various cells of the MPS can be induced to differentiate into cells capable of the highly specialized osteoclastic function of lacunar bone resorption. We isolated mouse and rat monocytes, mouse (liver, peritoneal, alveolar, brain) tissue macrophages, and spleen and marrow haemopoietic cells, as well as foreign body macrophages and macrophage polykaryons derived from subcutaneous granulomas formed by implantation of latex beads and coverslips in mice. When these cells were incubated with UMR106 osteoblast-like cells on glass coverslips and human cortical bone slices in the presence of 1,25-dihydroxy vitamin D₃ [1,25(OH)₂D₃] for 7 and 14 days, numerous tartrate-resistant acid phosphatase-positive cells formed in these co-cultures and scanning electron microscopy revealed extensive lacunar resorption of the bone surface. Bone resorption was seen as early as 4 days after monocytes were co-cultured with UMR106 cells. With the exception of bone marrow-derived cells, lacunar resorption was not seen in the absence of UMR106 cells. These findings show that a bone-derived stromal cell element is necessary for differentiation of monocytes and tissue and inflammatory macrophages into osteoclast-like cells capable of extensive lacunar bone resorption, and would argue in favour of osteoclast membership of the MPS.     

Ischemic stroke in rats enhances bone resorption in vitro

We hypothesized that the formation and differentialtion of osteoclasts are accelerated and the potential of bone resorption is increased in the hemiplegic bone marrow in the early stage of stroke. We randomly divided white female Sprague-Dawley (SD) rats (n = 30) into two groups, stroke (n = 15) and sham group (n = 15). On the 7th day after stroke, after cutting away the epiphyses of the femurs and tibias, diaphyseal channels were flushed using α-minimum essential medium (α-MEM) and bone marrow cells were collected. Bone marrow stem cells, which were extracted from the femur and tibia, were cultured on the 7th day after middle cerebral artery occlusion. We then estimated the ratio of non-adherent cells to total bone marrow cells that included osteoclast precursor cells. After culturing these cells separately, cells that tested positive on the tartrate resistant acid phosphatase (TRAP) were counted and bone resorption was evaluated by using the OAAS™ plate. In comparison to the control group, the stroke group showed a higher increase of non-adherent cells in the hemiplegic side bone marrow. In addition, after the primary culture, the stroke group showed an increased number of TRAP positive cells and a higher degree of bone resorption estimated by OAAS™ plate. As a result, osteoclastogenesis and osteoclast differentiation are accelerated and the potential of bone resorption is increased in the hemiplegic bone marrow and these changes are detected as early as within the first week after middle cerebral artery occlusion in SD rats.     

Genetic models show that parathyroid hormone and 1,25-dihydroxyvitamin D3 play distinct and synergistic roles in postnatal mineral ion homeostasis and skeletal development

In humans, loss-of-function mutations in parathyroid hormone (PTH) and 25-hydroxyvitamin D3-1alpha-hydroxylase [1alpha(OH)ase] genes lead to isolated hypoparathyroidism and vitamin D-dependent rickets type I, respectively. To better understand the relative contributions of PTH and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] to skeletal and calcium homeostasis, we compared mice with targeted disruption of the PTH or 1alpha(OH)ase genes to the double null mutants. Although PTH-/- and 1alpha(OH)ase-/- mice displayed only moderate hypocalcemia, PTH-/-1alpha(OH)ase-/- mice died of tetany with severe hypocalcemia by 3 weeks of age. At 2 weeks, PTH-/- mice exhibited only minimal dysmorphic changes, whereas 1alpha(OH)ase-/- mice displayed epiphyseal dysgenesis which was most severe in the double mutants. Although reduced osteoblastic bone formation was seen in both mutants, PTH deficiency caused only a slight reduction in long bone length but a marked reduction in trabecular bone volume, whereas 1alpha(OH)ase ablation caused a smaller reduction in trabecular bone volume but a significant decrease in bone length. The results therefore show that PTH plays a predominant role in appositional bone growth, whereas 1,25(OH)2D3 acts predominantly on endochondral bone formation. Although PTH and 1,25(OH)2D3 independently, but not additively, regulate osteoclastic bone resorption, they do affect the renal calcium transport pathway cooperatively. Consequently, PTH and 1,25(OH)2D3 exhibit discrete and collaborative roles in modulating skeletal and calcium homeostasis and loss of the renal component of calcium conservation might be the major factor contributing to the lethal hypocalcemia in double mutants.     

Decrease in Ca2+-ATPase activity in the brain plasma membrane of rats with increasing age: involvement of brain calcium accumulation

The alteration in Ca(2+)-ATPase activity in the brain plasma membrane of rats with increasing age was investigated. Calcium content in the brain tissues was significantly raised in aged rats (50 weeks old) as compared with that of young rats (5 weeks old). Increasing age caused a significant decrease in Ca(2+)-ATPase activity in the brain plasma membranes. The presence of N-ethylmaleimide (2.5 or 5 mM), a modifying reagent of thiol (SH)-groups, in the reaction mixture caused a significant decrease in the brain plasma membrane Ca(2+)-ATPase activity of young and aged rats, while dithiothreitol (2.5 or 5 mM), a protecting reagent of SH-groups, produced a significant increase in the enzyme activity, indicating that the SH-group is an active site of Ca(2+)-ATPase. The active site of Ca(2+)-ATPase may not be impaired by ageing. The brain plasma membrane Ca(2+)-ATPase activity of young rats was significantly reduced in the presence of dibutyryl cyclic AMP (10(-7)-10(-5) M) or inositol 1, 4, 5-trisphosphate (10(-7)-10(-5) M) in the reaction mixture. Such an decrease was not seen in aged rats. The responsibility for signaling factors seemed to be weakened by ageing. Calmodulin (2.5 and 5 microg/ml) or regucalcin (10(-8) and 10(-7) M), a Ca(2+)-regulating protein, did not have an effect on Ca(2+)-ATPase activity. This study demonstrates that ageing induces a decrease in Ca(2+)-ATPase activity in the brain plasma membranes. This finding suggests a cellular mechanism by which ageing causes calcium accumulation in brain.