Stimulation Of Calcium Uptake Research Articles

A case of nephrocalcinosis in a 7‐month‐old with congenital hypothyroidism: Insights from targeted exome sequencing

AbstractNephrocalcinosis is a complex disease with a multitude of triggering factors. An association with congenital hypothyroidism has been described in the literature, but the mechanisms leading to its development remain unclear. A 7‐month‐old infant presented with muscular hypotonia and signs of malnutrition was diagnosed with congenital hypothyroidism, nephrocalcinosis of unclear origin, and multiple kidney stones. Urine analysis revealed the presence of calcium oxalate crystals and slightly elevated oxaluria without hypercalciuria. Targeted exome sequencing found no variants in the four causative genes of primary oxaluria, namely AGXT, CBX5, GRHPR, and HOGA1. The clinical outcome was favorable with thyroid hormone and potassium citrate treatment. Ultrasound follow‐up showed progressive improvement of nephrocalcinosis. The low level of urinary oxalate and the prevalence of dihydrate calcium oxalate crystals spoke against primary or secondary oxaluria. Recent evidence from mitochondrial research shows that thyroid hormone T3 enhances mitochondrial calcium levels by stimulating calcium uptake by the mitochondrial calcium uniporter. A reduced calcium uptake and metabolism in mitochondria might represent an explanation for cytoplasmic calcium accumulation in tubular cells, subsequently precipitating nephrocalcinosis in the absence of thyroid hormone. Even if the pathophysiological mechanisms are not yet fully understood, recent evidence is supportive of a causal relationship between hypothyroidism and nephrocalcinosis, a sometimes overlooked association.

Effect of calcium on relieving berry cracking in grape (Vitis vinifera L.) 'Xiangfei'.

Fruit cracking is a physiological disorder in many plant species that leads to severe economic losses. The aim of this study was to investigate the effect of calcium on fruit cracking and explore the underlying mechanisms. We studied the effect of exogenous calcium on grape berry cracking, calcium absorbance and distribution, and cell wall metabolism in the cracking-susceptible cultivar ‘Xiangfei’. Calcium significantly reduced the frequency of fruit cracking, increased the break force of the berry skin, and stimulated storage of calcium. In addition, calcium increased the content of protopectin and inhibited the increase in content of water-soluble pectin, by regulating the transcription and activities of enzymes associated with cell wall metabolism. Taken together, the results indicated that dipping grape berries in calcium solution is effective in preventing fruit cracking by stimulating calcium uptake, inhibiting cell wall disassembly, and promoting cell wall strengthening.

Inorganic polyphosphate is required for sustained free mitochondrial calcium elevation, following calcium uptake

Mitochondrial free calcium is critically linked to the regulation of cellular metabolism. Free ionic calcium concentration within these organelles is determined by the interplay between two processes: exchange across the mitochondrial inner membrane and calcium-buffering within the matrix. During stimulated calcium uptake, calcium is primarily buffered by orthophosphate, preventing calcium toxicity while allowing for well-regulated yet elevated calcium loads. However, if limited to orthophosphates only, this buffering system is expected to lead to the irreversible formation of insoluble precipitates, which are not observed in living cells, under physiological conditions. Here, we demonstrate that the regulation of free mitochondrial calcium requires the presence of free inorganic polyphosphate (polyP) within the organelle. We found that the overexpression of a mitochondrial-targeted enzyme hydrolyzing polyP leads to the loss of the cellular ability to maintain elevated calcium concentrations within the organelle, following stimulated cytoplasmic signal. We hypothesize that the presence of polyP prevents the formation of calcium-phosphate insoluble clusters, allowing for the maintenance of elevated free calcium levels, during stimulated calcium uptake.

Flowering and nutritional status of Gladiolus hybridus L. 'Black Velvet' following gibberellin treatment

Flowering and nutritional status in Gladiolus hybridus L. ‘Black Velvet’ were assessed following gibberellic acid treatment (GA<sub>3</sub>). Treatment were applied to corm (12–14 diameter) by soaking for 30 min in water solutions of GA<sub>3</sub> at 100, 350 and 600 mg/dm<sup>3 </sup>with a control consisting of soaking-in water. All GA<sub>3</sub> treatments inhibited elongation of inflorescence shoots and stimulated spike elongation. None of the tested concentrations affected the number of developing flowers in the spike, except for the 100 mg/dm<sup>3</sup> in the 2nd year of the study. All GA<sub>3</sub> treatments stimulated calcium uptake, but had no effect on the uptake of other macronutrients. All the GA<sub>3</sub> treatments increased manganese content in leavesbud did not affect copper content. GA<sub>3</sub> at 600 mg/dm<sup>3</sup> stimulated uptake of iron and boron at 600 mg/dm<sup>3</sup> but inhibited both at lower concentrations. Zinc uptake was stimulated at 100 mg/dm<sup>3 </sup>but inhibited at higher concentration.

Parathyroid Hormone-Related Protein (1-40) Enhances Calcium Uptake in Rat Enterocytes Through PTHR1 Receptor and Protein Kinase Cα/β Signaling

Background/Aims: Parathyroid hormone-related protein (PTHrP) is implicated in regulating calcium homeostasis in vertebrates, including sea bream, chick, and mammals. However, the molecular mechanism underlying the function of PTHrP in regulating calcium transport is still not fully investigated. This study aimed to investigate the effect of PTHrP on the calcium uptake and its underlying molecular mechanism in rat enterocytes. Methods: The rat intestinal epithelial cell line (IEC-6) was used. Calcium uptake was determined by using the fluo-4 acetoxymethyl ester fluorescence method. The expression levels of RNAs and proteins was assessed by RT-PCR and Western-blot, respectively. Results: PTHrP (1-40) induced rapid calcium uptake in enterocytes in a dose-dependent manner. PTHrP (1-40) up-regulated parathyroid hormone 1 receptor (PTHR1) protein but not 1,25D3-MARRS receptor. Pre-treatment of anti- PTHR1 antibody abolished the PTHrP (1-40)-induced calcium uptake. PTHrP (1-40) significantly up-regulated four transcellular calcium transporter proteins, potential vanilloid member 6 (TRPV6), calbindin-D9k (CaBP-D9k), sodium-calcium exchanger 1 (NCX1) and plasma membrane calcium ATPase 1 (PMCA1), in a dose- and time-dependent manner. Pre-treatment with TRPV6 or CaBP-D9k antibodies or knockout of rat TRPV6 or CaBP-D9k markedly inhibited PTHrP (1-40)-induced calcium uptake, whereas inhibition of NCX or PMCA1 by antibodies or inhibitors had no effect on PTHrP(1-40)-induced calcium uptake. Furthermore, PTHrP (1-40) treatment up-regulated protein levels of protein kinase C (PKC α/β) and protein kinase A (PKA). Pretreatment of PKC α/β inhibitor (but not PKA inhibitor) inhibited PTHrP (1-40)-induced calcium uptake. Conclusion: PTHrP (1-40) stimulates calcium uptake via PTHR1 receptor and PKC α/β signaling pathway in rat enterocytes, and calcium transporters TRPV6 and CaBP-D9k are necessary for this stimulatory effect.

Vitamin D and gonadal function in men: a potential inverse U‐shaped association?

Accumulating evidence from animal and human studies suggests that vitamin D, apart from its regulatory effects on musculoskeletal health, is involved in reproductive function in both genders. The basis of the interplay between vitamin D and reproduction lays on the presence of both vitamin D receptor (VDR) and 1α-hydroxylase (CYP27B1) enzyme in reproductive organs. In males, VDR are present in testis, epididymis, prostate, and seminal vesicles. In Sertoli cells, whose secretory activities are ion channel-dependent, vitamin D has been shown to stimulate calcium uptake through a nuclear receptor activity. Epidemiological studies support a positive association between serum 25-hydroxy-vitamin D [25(OH)D] concentrations and sperm motility in both fertile and infertile men In addition, large multi-center, cross-sectional studies from Europe and USA have shown positive, linear association between 25(OH)D and androgen concentrations. On the contrary, there are studies that support an inverse U-shaped association, that is, men with both low and high 25(OH)D concentrations demonstrate poorer gonadal function compared with those with intermediate concentrations. Given the rapid increase in over-the-counter use of vitamin D supplements by men that anticipate advantageous health outcomes, the aim of the present commentary is to provide an overview of the studies that present either U-shaped or linear association between 25(OH)D concentrations and male gonadal function.

Splicing reverses protein’s function

![Figure][1] STIM2α (green, left) binds to Orai1 channels (red), but STIM2β (green, right) doesn’t. Alternative splicing transforms a protein that stimulates calcium uptake into one that inhibits it, [Rana et al.][2] discover. The proteins STIM1 and STIM2 sense when the endoplasmic

The 1,25D3 -MARRS receptor/PDIA3/ERp57 and lifespan.

Using MRI on mice bearing a targeted knockout (KO) of the 1,25D3 -MARRS receptor/PDIA3/ERp57 we found that they had decreased body fat relative to their littermate (LM) controls, a condition associated with increased lifespan. Others have found that lower body fat is correlated with decreased lipid droplets in intestinal cells that may be mediated by a factor secreted by germ cells (possibly estradiol). In a reducing environment estradiol competed for binding to the 1,25D3-MARRS receptor/PDIA3/ERp57. A consequence of this was that estradiol stimulated calcium uptake in enterocytes isolated from LM mice. In time course studies, lipid droplets increased in response to 1 nM estradiol from 1-5 D of culture, relative to corresponding controls, while at 6 and 7 D this steroid decreased lipid droplets. Enterocytes from LM or KOs incubated with estradiol for 1-4 D showed the hormone increased lipid droplets. Using the 4 D culture period, 1 and 10 nM estradiol significantly increased the number of lipid droplets in cells from LM mice by 40-60%, compared to equivalent conditions in KO mice. In assessing signal transduction pathways, the hormone increased phospho-Akt levels, but no differences were observed in phospho-mTORC1, or phospho-S6K (although cells from chicks did exhibit a hormone-mediated difference). Finally, the remaining mice (which had stopped reproducing) were allowed to die naturally and lifespan recorded. LM mice lived 687 ± 77 D (without an outlying value) while KO mice lived 740 D ± 80 D. These data suggest the 25D3 -MARRS receptor/PDIA3/ERp57 may contribute to the length of lifespan in mammals.

Non-classical effects of androgens on testes from neonatal rats

The intratesticular testosterone concentration is high during the early postnatal period although the intracellular androgen receptor expression (iAR) is still absent in Sertoli cells (SCs). This study aimed to evaluate the non-classical effects of testosterone and epitestosterone on calcium uptake and the electrophysiological effects of testosterone (1μM) on SCs from rats on postnatal day (pnd) 3 and 4 with lack of expression of the iAR. In addition, crosstalk on the electrophysiological effects of testosterone and epitestosterone with follicle stimulating hormone (FSH) in SCs from 15-day-old rats was evaluated. The isotope 45Ca2+ was utilized to evaluate the effects of testosterone and epitestosterone in calcium uptake. The membrane potential of SCs was recorded using a standard single microelectrode technique. No immunoreaction concerning the iAR was observed in SCs on pnd 3 and 4. At this age, both testosterone and epitestosterone increased the 45Ca2+ uptake. Testosterone promoted membrane potential depolarization of SCs on pnd 4. FSH application followed by testosterone and epitestosterone reduced the depolarization of the two hormones. Application of epitestosterone 5min after FSH resulted in a delay of epitestosterone-promoted depolarization. The cell resistance was also reduced. Thus, in SCs from neonatal Wistar rats, both testosterone and epitestosterone act through a non-classical mechanism stimulating calcium uptake in whole testes, and testosterone produces a depolarizing effect on SC membranes. Testosterone and epitestosterone stimulates non-classical actions via a membrane mechanism, which is independent of iAR. FSH and testosterone/epitestosterone affect each other’s electrophysiological responses suggesting crosstalk between the intracellular signaling pathways.

Vitamin D and gene networks in human osteoblasts

Bone formation is indirectly influenced by 1,25-dihydroxyvitamin D3 (1,25D3) through the stimulation of calcium uptake in the intestine and re-absorption in the kidneys. Direct effects on osteoblasts and bone formation have also been established. The vitamin D receptor (VDR) is expressed in osteoblasts and 1,25D3 modifies gene expression of various osteoblast differentiation and mineralization-related genes, such as alkaline phosphatase (ALPL), osteocalcin (BGLAP), and osteopontin (SPP1). 1,25D3 is known to stimulate mineralization of human osteoblasts in vitro, and recently it was shown that 1,25D3 induces mineralization via effects in the period preceding mineralization during the pre-mineralization period. For a full understanding of the action of 1,25D3 in osteoblasts it is important to get an integrated network view of the 1,25D3-regulated genes during osteoblast differentiation and mineralization. The current data will be presented and discussed alluding to future studies to fully delineate the 1,25D3 action in osteoblast. Describing and understanding the vitamin D regulatory networks and identifying the dominant players in these networks may help develop novel (personalized) vitamin D-based treatments. The following topics will be discussed in this overview: (1) Bone metabolism and osteoblasts, (2) Vitamin D, bone metabolism and osteoblast function, (3) Vitamin D induced transcriptional networks in the context of osteoblast differentiation and bone formation.

PI3K-dependent actions of insulin and IGF-I on seminiferous tubules from immature rats

There is clear evidence that insulin and insulin-like growth factor I (IGF-I) are crucial for the normal metabolism and development of Sertoli cells. However, the mechanisms of insulin regulatory signaling remain unknown in these cells, especially during the immature period. The aim of this study was to investigate the electrophysiological effects of insulin and the effects of insulin and IGF-I on calcium uptake, amino acid, and glucose transport in whole seminiferous tubules from 12-day-old rats, as well as the involvement of PI3K/Akt signaling pathway in these effects. Insulin produces a depolarizing effect on the membrane potential of Sertoli cells in seminiferous tubules within 180 s. This effect was nullified by verapamil, an L-type voltage-dependent calcium channel blocker, therefore demonstrating a calcium-dependent depolarizing effect. Both insulin and IGF-I stimulate calcium uptake, amino acid, and glucose transport in whole testes from 12-day-old rats. These stimulatory effects of insulin and IGF-I on calcium uptake and amino acid and glucose transport on testicular tissue were nullified by wortmannin, which demonstrates the involvement of the PI3K/Akt signaling pathway in these hormonal effects.

Rutin potentiates calcium uptake via voltage-dependent calcium channel associated with stimulation of glucose uptake in skeletal muscle

Rutin is a flavonoid with several pharmacological properties and it has been demonstrated that rutin can modulate glucose homeostasis. In skeletal muscle, an increase in intracellular calcium concentration may induce glucose transporter-4 (GLUT-4) translocation with consequent glucose uptake. The aim of this study was to investigate the effect of rutin and intracellular pathways on calcium uptake as well as the involvement of calcium in glucose uptake in skeletal muscle. The results show that rutin significantly stimulated calcium uptake through voltage-dependent calcium channels as well as mitogen-activated kinase (MEK) and protein kinase A (PKA) signaling pathways. Also, rutin stimulated glucose uptake in the soleus muscle and this effect was mediated by extracellular calcium and calcium–calmodulin-dependent protein kinase II (CaMKII) activation. In conclusion, rutin significantly stimulates calcium uptake in rat soleus muscles. Furthermore, the increase in intracellular calcium concentration is involved in DNA activation by rutin. Also, rutin-induced glucose uptake via CaMKII may result in GLUT-4 translocation to the plasma membrane, characterizing an insulin-independent pathway. These findings indicate that rutin is a potential drug candidate for diabetes therapy.

Chitosan Stimulates Calcium Uptake and Enhances the Capability of Chinese Cabbage Plant to Resist Soft Rot Disease Caused by Pectobacterium carotovorum ssp. carotovorum

Chinese cabbage plant was grown hydroponically for 4 weeks in order to examine the temporal relationship of calcium concentration of the nutrient solution with calcium content in the leaf tissue and susceptibility of the tissue to soft rot disease by Pectobacterium carotovorum ssp. carotovorum (Pcc). Calcium concentration from 0.5 to 32.0 mM was maintained for 1 week using Hoagland & Arnon solution. The calcium content of the leaf was proportionally increased to the concentration of the nutrient in the solution (r = 0.912). In contrast, the severity of soft rot symptom in the young leaves was inversely related with the amount of calcium supplied to the nutrient solution (r = 0.899). Water-soluble chitosan, prepared by hollow fiber filtration (＞ 100 kDa) was applied into the nutrient solution from 0.0 to 5,000 ppm. The chitosan of 10 ppm was the most effective to promote calcium uptake of the leaf, showing 155% of the control. The same chitosan solution prohibited most soft rot development of the leaf by Pcc, exhibiting only 53% of the control. Among different molecular weight fractions, chitosan fraction obtained from 30-100 kDa molecular weight cut-off promoted calcium uptake the most up to 163% of the control, and reduced the development of soft rot disease recording merely 36% of the control of the leaf tissue. The results obtained in the present study suggest that large scale production of water-soluble chitosan with an optimum molecular weight and its commercial application to Chinese cabbage production will be important to improve yield and quality of the crop.

Effect of 1α,25-dihydroxyvitamin D3 in plasma membrane targets in immature rat testis: Ionic channels and gamma-glutamyl transpeptidase activity

1α,25-Dihydroxyvitamin D3 (1,25D3) is critical for the maintenance of normal reproduction since reduced fertility is observed in vitamin D-deficient male rats. The aim of this study was to investigate the effect of 1,25D3 in 30-day-old rat testicular plasma membrane targets (calcium uptake and gamma-glutamyl transpeptidase (GGTP) activity), as well as to highlight the role of protein kinases in the mechanism of action of 1,25D3. The results demonstrated that 1,25D3 induced a fast increase in calcium uptake in rat testis through a nongenomic mechanism of action. This effect was dependent on PKA, PKC and MEK. Moreover, ionic channels, such as ATP- and Ca2+-dependent K+ channels and Ca2+-dependent Cl− channels, are involved in the mechanism of action. The use of BAPTA-AM showed that [Ca2+]i was also implicated, and the incubation with digoxin produced an increase in 45Ca2+ uptake indicating that the effect of 1,25D3 may also result from Na+/K+-ATPase inhibition. In addition, 1,25D3 was able to increase the GGTP activity. Considered together, our results indicate a PKA/PKC/MEK-dependent 1,25D3 pathway as well as ionic involvement leading to 45Ca2+ uptake in immature rat testis. These findings demonstrate that 1,25D3 stimulates calcium uptake and increases GGTP activity which may be involved in male reproductive functions.

Intestinal Cell Calcium Uptake and the Targeted Knockout of the 1,25D3-MARRS (Membrane-associated, Rapid Response Steroid-binding) Receptor/PDIA3/Erp57

We have crossed ERp57(flx/flx) mice with commercially available mice expressing villin-driven cre-recombinase. Lysates of intestinal epithelial cells were prepared from knock-out (KO) mice and littermates (LM) and used in Western blot analyses with Ab099 against the N terminus of the 1,25D(3)-MARRS (membrane-associated, rapid response steroid-binding) receptor: LM mice exhibited one positive band, which was absent in preparations from KO mice. Saturation analyses of cell lysates with [(3)H]1,25D(3) revealed negligible binding in preparations from either female or male KOs. Lysates from female and male LM mice had similar affinities but different numbers of binding sites. Isolated enterocytes were tested for steroid-stimulated calcium uptake. Treatment of cells from female or male LM mice with 1,25D(3) elicited enhanced calcium uptake in females and males within 5 min. Intestinal cells from KO mice exhibited a severely blunted or completely absent response to hormone. Confocal microscopy of intestinal cells revealed the presence of cell surface vitamin D receptors. However, antibodies to the vitamin D receptor failed to block 1,25D(3)-stimulated calcium uptake. In chick enterocytes we have found that the PKA pathway mediates calcium uptake. The time course for activation of PKA in mouse enterocytes paralleled that for enhanced calcium uptake and for LM females reached 250% of controls within 5 min, and 150% of controls in cells prepared from LM males. Enterocytes from female or male KO mice failed to exhibit steroid hormone-stimulated PKA activity, but did respond to forskolin with enhanced calcium uptake. We conclude that the 1,25D(3)-MARRS receptor is of central importance to steroid hormone-stimulated calcium uptake in mammalian intestinal cells.

Intestinal Cell Calcium Uptake and the Targeted Knockout Of the 1,25D3‐MARRS Receptor/PDIA3/Erp57

We have crossed ERp57lfx/flx mice with mice expressing villin‐driven cre‐recombinase. Lysates of enterocytes from knockout (KO) mice and littermates (LM) were used in Western analyses with Ab099 against the N‐terminus of the 1,25D3‐MARRS receptor: LM mice exhibited one positive band, which was absent in preparations from KO mice. Saturation analyses of cell lysates with [3H]1,25D3 revealed negligible binding in either female or male KOs. Lysates from female and male LM mice had similar affinities but different numbers of binding sites. Isolated enterocytes were tested for steroid stimulated calcium uptake. Treatment of cells from female or male LM mice with 1,25D3 elicited enhanced within 5 min. Intestinal cells from KO mice exhibited a severely blunted or completely absent response to hormone. Confocal microscopy of intestinal cells revealed the presence of cell‐surface VDR. However, antibodies to the VDR failed to block 1,25D3‐ stimulated calcium uptake. In chick enterocytes we have found that the PKA pathway mediates calcium uptake. The time course for activation of PKA in mouse enterocytes paralleled that for enhanced calcium uptake. Enterocytes from female or male KO mice failed to exhibit 1,25D3 stimulated PKA activity, but did respond to forskolin with enhanced calcium uptake. We conclude that the 1,25D3‐MARRS receptor is of central importance to steroid hormone stimulated calcium uptake in mammalian intestinal cells.

Casein phosphopeptides promote calcium uptake and modulate the differentiation pathway in human primary osteoblast-like cells

Casein phosphopeptides (CPPs), originating by in vitro and/or in vivo casein digestion, are characterized by the ability to complex and solubilize calcium ions preventing their precipitation. Previous works demonstrated that CPPs improve calcium uptake by human differentiated intestinal tumor cell lines, are able to re-mineralize carious lesions in a dental enamel, and, as components of a diet, affect bone weight and calcium content in rats. The aim of the present study was to evaluate if CPPs can directly modulate bone cells activity and mineralization. Primary human osteoblast-like cells were established in culture from trabecular bone samples obtained from waste materials during orthopedic surgery. Commercial mixtures of bovine casein phosphopeptides were used. The CPP dependent intracellular calcium rises were monitored at the single cell level through fura2-fluorescence assays. Results show that CPPs: (i) stimulate calcium uptake by primary human osteoblast-like cells; (ii) increase the expression and activity of alkaline phosphatase, a marker of human osteoblast differentiation; (iii) affect the cell proliferation rate and the apoptotic level; (iv) enhance nodule formation by human SaOS-2. Taken together these results confirm the possibility that CPPs play a role as modulator of bone cell activity, probably sustained by their ability as calcium carriers. Although the exact mechanism by which CPPs act remains not completely clarified, they can be considered as potential anabolic factors for bone tissue engineering.

The 1,25D 3-MARRS protein: Contribution to steroid stimulated calcium uptake in chicks and rats

There are currently two main candidates for the membrane receptor for 1,25(OH) 2D 3: the 1,25D 3-MARRS protein/ERp57; and the classical VDR. The 1,25D 3-MARRS protein is essential for hormone-stimulated phosphate and calcium uptake in chick intestinal cells, whereas the VDR is not. The 1,25D 3-MARRS protein also shows a high degree of correlation with growth periods in which bone is rapidly formed, whereas the VDR does not. However, in rat enterocytes, both the 1,25D 3-MARRS protein and the VDR play a role in the rapid, steroid-mediated uptake of phosphate or calcium. Therefore, the theory that alternate binding sites on the VDR for various analogs account for all membrane-initiated phenomena, is incorrect.

Functional expression of human and mouse P2Y12 receptors in Saccharomyces cerevisiae

DNA sequences encoding the murine ortholog of the human P2Y12 receptor were cloned. The human and mouse P2Y12 receptors were expressed in a yeast cell-based GPCR expression technology containing chimeric yeast Gα protein (Gpa1) constructs in which the 5 C-terminal amino acids were identical to corresponding sequences from mammalian Gαi/o proteins. LacZ reporter gene assays of agonist-induced activation of the G protein-coupled mating signal transduction pathway revealed murine P2Y12 functional pharmacological properties that closely resembled those exhibited by the human P2Y12 receptor. In NIH3T3 cells, the mouse P2Y12 stimulated calcium uptake monitored in FLIPR via coupling to a Gαq/i3 chimeric protein. Murine P2Y12 mRNA was expressed at high levels in the brain and at lower levels in a variety of peripheral tissues. In situ hybridization analysis indicated glia-specific expression within the brain.

Effect of tri- o-cresyl phosphate and methamidophos on 45Ca uptake by brain synaptosomes in hens

The effect of tri- o-cresyl phosphate (TOCP) and methamidophos (MET) on potassium-stimulated 45Ca uptake by brain synaptosomes in hens was studied. An in vivo test showed that TOCP increased potassium-stimulated calcium uptake 2 h after its administration, but that verapamil suppressed the enhancement of this calcium uptake. An in vitro test showed that lower concentrations of TOCP stimulated calcium uptake by synaptosomes, but that higher concentrations inhibited the uptake. In contrast, all tested concentrations of MET obviously inhibited calcium uptake; however, since calcium uptake was decreased by the administration of verapamil plus either TOCP or MET, the mechanism by which TOCP affects the voltage-operated calcium channel may be different from that of MET. The disruption of calcium homeostasis may be involved in organophosphate-induced delayed neurotoxicity (OPIDN). Calcium channel blocker may ameliorate OPIDN by maintaining calcium homeostasis in nerve cells.