Neuronal Calcium Homeostasis Research Articles

Plasma membrane Ca 2+-ATPase isoforms: distribution of mRNAs in rat brain by in situ hybridization

Several mRNAs which encode for isoforms of the plasma membrane Ca 2+-transport ATPase (PMCA) are present in adult rat brain. Using in situ hybridization with antisense oligonucleotide probes we found complex patterns of specific hybridization for three isoforms (PMCA1–3). Each rat brain region studied exhibited a distinct pattern of expression of isoforms. PMCA1 mRNA, which is widely distributed in rat tissues, was highest in CA1 pyramidal cells of hippocampus and very low in hypothalamic nuclei, cerebellum and choroid plexus. PMCA2 mRNA was highest in Purkinje cells of cerebellum and low in caudate-putamen, hypothalamic nuclei, habenula and choroid plexus. The highest levels of PMCA3 mRNA were found in habenula and choroid plexus. The PMCA1–3 isoforms appeared to be expressed primarily in neurons since hybridization was detected neither in white matter nor in regions rich in astrocytes. In different regions, different levels of expression of each PMCA mRNA may underlie specialized requirements for calcium homeostasis in specific neurons.

Pardaxin-stimulated calcium uptake in PC12 cells is blocked by cadmium and is not mediated by L-type calcium channels.

Pardaxin is an excitatory neurotoxin which triggers neurotransmitter release as a result of voltage-dependent pore formation within the neuronal membrane. We have used several pharmacological manipulations of calcium influx to characterize pardaxin pore activity in PC12 cells in culture. Pardaxin stimulates the uptake of radioactive calcium into PC12 cells in a dose dependent fashion (ED50 of 0.4 microM). This stimulation is partially inhibited by nifedipine, a blocker of L-type calcium channels. Effective blockade of pardaxin stimulation was produced by the inorganic calcium channel blockers cadmium (IC50 of 10 microM) and nickel (2 mM). Homologous down regulation of L-calcium channels by the agonist Bay K-8644, inhibited the subsequent stimulation of calcium uptake by this drug, but not by pardaxin. A fluorometric analysis of pardaxin pore formation in unilamellar large liposomes indicates pardaxin pores are blocked by cadmium (10-200 microM). These data distinguish between pardaxin pores and L-type calcium channels in PC12 cells. We suggest pardaxin as a pharmacological ionophore tool to modulate neuronal calcium homeostasis and neurotransmitter release.

IGF-I and IGF-II protect cultured hippocampal and septal neurons against calcium-mediated hypoglycemic damage

Insulin and insulin-like growth factors I and II (IGF-I and IGF-II) have recently been shown to have biological activity in central neurons, but their normal functions and mechanisms of action in the brain are unknown. Since central neurons are particularly vulnerable to hypoglycemia that results from ischemia or other insults, we tested the hypothesis that growth factors can protect central neurons against hypoglycemic damage in vitro. IGF-I and IGF-II (3-100 ng/ml) each prevented glucose deprivation-induced neuronal damage in a dose-dependent manner in rat hippocampal and septal cell cultures. High concentrations of insulin (greater than 1 microgram/ml) also protected neurons against hypoglycemic damage. Epidermal growth factor did not protect against hypoglycemic damage. Both IGFs and insulin were effective when administered 24 hr before or immediately following the onset of glucose deprivation. Direct measurements of intraneuronal calcium levels and manipulations of calcium influx demonstrated that calcium influx and sustained elevations in intraneuronal calcium levels mediated the hypoglycemic damage. IGF-I and IGF-II each prevented the hypoglycemia-induced elevations of intraneuronal free calcium. Studies with excitatory amino acid receptor antagonists and calcium channel blockers indicated that NMDA receptors did, and L-type calcium channels did not, play a major role in hypoglycemic damage. Taken together, these findings indicate that IGFs can stabilize neuronal calcium homeostasis and thereby protect against hypoglycemic damage.

Beta-Amyloid peptides destabilize calcium homeostasis and render human cortical neurons vulnerable to excitotoxicity

In Alzheimer's disease (AD), abnormal accumulations of beta-amyloid are present in the brain and degenerating neurons exhibit cytoskeletal aberrations (neurofibrillary tangles). Roles for beta-amyloid in the neuronal degeneration of AD have been suggested based on recent data obtained in rodent studies demonstrating neurotoxic actions of beta-amyloid. However, the cellular mechanism of action of beta-amyloid is unknown, and there is no direct information concerning the biological activity of beta-amyloid in human neurons. We now report on experiments in human cerebral cortical cell cultures that tested the hypothesis that beta-amyloid can destabilize neuronal calcium regulation and render neurons more vulnerable to environmental stimuli that elevate intracellular calcium levels. Synthetic beta-amyloid peptides (beta APs) corresponding to amino acids 1-38 or 25-35 of the beta-amyloid protein enhanced glutamate neurotoxicity in cortical cultures, while a peptide with a scrambled sequence was without effect. beta APs alone had no effect on neuronal survival during a 4 d exposure period. beta APs enhanced both kainate and NMDA neurotoxicity, indicating that the effect was not specific for a particular subtype of glutamate receptor. The effects of beta APs on excitatory amino acid (EAA)-induced neuronal degeneration were concentration dependent and required prolonged (days) exposures. The beta APs also rendered neurons more vulnerable to calcium ionophore neurotoxicity, indicating that beta APs compromised the ability of the neurons to reduce intracellular calcium levels to normal limits. Direct measurements of intracellular calcium levels demonstrated that beta APs elevated rest levels of calcium and enhanced calcium responses to EAAs and calcium ionophore. The neurotoxicity caused by EAAs and potentiated by beta APs was dependent upon calcium influx since it did not occur in calcium-deficient culture medium. Finally, the beta APs made neurons more vulnerable to neurofibrillary tangle-like antigenic changes induced by EAAs or calcium ionophore (i.e., increased staining with tau and ubiquitin antibodies). Taken together, these data suggest that beta-amyloid destabilizes neuronal calcium homeostasis and thereby renders neurons more vulnerable to environmental insults.

Roles for amyloid precursor proteins and β-amyloid in the regulation and misregulation of neuronal calcium homeostasis: M. P. Mattson, B. Cheng, I. Lieberburg and R. E. Rydel. Sanders-Brown Research Center on Aging, Department of Anatomy & Neurobiol. University of Kentucky, Lexington, KY 40536; Athena Neurosciences Inc., South San Francisco, CA 94080, USA

Roles for amyloid precursor proteins and β-amyloid in the regulation and misregulation of neuronal calcium homeostasis: M. P. Mattson, B. Cheng, I. Lieberburg and R. E. Rydel. Sanders-Brown Research Center on Aging, Department of Anatomy & Neurobiol. University of Kentucky, Lexington, KY 40536; Athena Neurosciences Inc., South San Francisco, CA 94080, USA

Astrocyte-derived growth factors affect neuronal calcium homeostasis: Roles in neuron survival and plasticity

This chapter reviews recent concepts of chemical communication between excitable cells, with particular emphasis on the co-existence of transmitter substances in single nerve terminals. While the classical view is that the autonomic nervous system (ANS) consists largely of antagonistic cholinergic and adrenergic nerves, about fourteen putative neurotransmitters in the ANS have been proposed in the past few years, including various monoamines, polypeptides, purines, and amino acids. Modulatory transmitter mechanisms have also been recognized, including prejunctional inhibition or enhancement of transmitter release, postjunctional modulation of transmitter action, and the secondary involvement of locally synthesized hormones and prostaglandins. The co-transmitters always have synergistic actions on postjunctional effector cells, but two different mechanisms are postulated. (1) If both substances are stored in the same vesicles, release is closely parallel at all impulse frequencies. Upon release, the co-transmitter, in addition to having a direct action on postjunctional cells, may facilitate the action of the other transmitter and act as an inhibitor of its release. (2) If the two substances are stored in separate and different vesicle types, differential release is possible at different impulse frequencies. The peptides released at higher frequencies modulate the role of the classical transmitter, by both prejunctional enhancement of its release and postjunctional facilitation of its action.

Phosphate/calcium alterations in the first stages of Alzheimer's disease: Implications for etiology and pathogenesis

The present study tested aspects of a novel etiological/pathogenetic hypothesis of Alzheimer's disease (AD), which proposes that alterations in endocrine regulation of peripheral calcium/phosphate ( Ca PO 4 ) homeostasis (e.g., by glucocorticoids, vitamin D, etc.) induce and/or reflect altered calcium homeostasis and neurotoxicity in brain neurons. Two key predictions of this hypothesis were tested, namely that: (1) alterations in serum Ca and/or PO 4 regulation should be present before or near the onset of AD and (2) these alterations should be found consistently in subjects with unconfounded AD. Previous studies have sought evidence of changes in Ca regulation primarily late in the disease, and usually in severely demented, thin and immobile inpatients in whom Ca PO 4 measures are likely to be confounded. In the present study, only mobile, relatively healthy, adequately nourished outpatients with probable AD were selected. In comparison to age-matched controls or demented subjects with even mild indications of vascular contributions, the AD subjects were characterized by lower serum PO 4 and, to a lesser degree, lower serum Ca as well as a higher chloride PO 4 ratio. On serum chemistry tests from the first stages of AD (within 1 or 3 years after the onset of cognitive symptoms), these changes in serum PO 4 Ca were as pronounced as they were later in the disease. Moderately low values of either PO 4, Ca, or both (below −1.0 S.D. from the control group mean) identified 74% of all AD subjects and 100% of early onset AD subjects, in comparison to only 46% of mixed/vascular dementia subjects and 31% of normal age-matched controls. Thus, the results were consistent with the predictions and may have significant etiological/pathogenetic implications. If larger tests confirm these frequencies, serum Ca PO 4 indices may also prove useful in differential diagnosis.

NGF and bFGF protect rat hippocampal and human cortical neurons against hypoglycemic damage by stabilizing calcium homeostasis

NGF and bFGF have recently been shown to have biological activity in central neurons, but their normal functions and mechanisms of action are unknown. Since central neurons are particularly vulnerable to hypoglycemia that occurs with ischemia or insulin overdose, we tested the hypothesis that growth factors can protect neurons against hypoglycemic damage. NGF and bFGF each prevented glucose deprivation-induced neuronal damage in human cerebral cortical and rat hippocampal cell cultures (EGF was ineffective). Protection was afforded when the growth factors were administered before (NGF and bFGF) or up to 12 hr following (NGF) the onset of hypoglycemia. Direct measurements of intracellular calcium levels and manipulations of calcium influx demonstrated that sustained elevations in intracellular calcium levels mediated the hypoglycemic damage. NGF and bFGF each prevented the hypoglycemia-induced elevations of intracellular calcium. These findings indicate that growth factors can stabilize neuronal calcium homeostasis in central neurons and thereby protect them against environmental insults.

Effects of elevated intracellular calcium levels on the cytoskeleton and tau in cultured human cortical neurons.

Considerable evidence suggests that altered neuronal calcium homeostasis plays a role in the neuronal degeneration that occurs in an array of neurological disorders. A reduction in microtubules, the accumulation of 8-15 nm straight filaments, and altered antigenicity toward antibodies to the microtubule-associated protein tau and ubiquitin, as well as granulovacuolar degeneration, are observed in many human neurodegenerative disorders. Progress toward understanding how and why human neurons degenerate has been hindered by the inability to examine living human neurons under controlled conditions. We used cultured human fetal cerebral cortical neurons to examine ultrastructural and antigenic changes resulting from elevations in intracellular calcium levels. Elevation of intracellular calcium by exposure to a calcium ionophore or a reduced level of extracellular Na+ for periods of hours to days caused a loss of microtubules, an increase in 8-15 nm straight filaments, and increased immunostaining with Alz-50 and 5E2 (tau antibodies) and ubiquitin antibodies. Granulovacuolar degeneration was also observed. Antigenic changes in tau were sensitive to phosphatases, and the electrophoretic mobility of tau was altered in cells exposed to calcium ionophore, indicating that tau was excessively phosphorylated as the result of elevated intracellular calcium levels. Colchicine also caused an accumulation of straight filaments and altered tau immunoreactivity, suggesting that a disruption of microtubules secondary to altered calcium homeostasis may be a key event leading to altered tau disposition and neuronal degeneration. These data demonstrate that aberrant rises in intraneuronal calcium levels can result in changes in the neuronal cytoskeleton similar to those seen in neurodegenerative disorders, and suggest that this experimental system will be useful in furthering our understanding of the cellular and molecular mechanisms of human neurological disorders.

Neuron-specific and state-specific differences in calcium homeostasis regulate the generation and degeneration of neuronal architecture

Many stimuli (e.g., neurotransmitters and electrical activity) regulate neuromorphogenesis by changing intracellular calcium. The ionophore A23187 was employed as a receptor-independent method to investigate neuronal calcium homeostasis. Distinctive neuron-specific (B5 versus B19) and state-specific (growing versus nong-rowing) differences in calcium homeostasis were observed in cultured identified Helisoma neurons. Fura-2 studies revealed that A23187 induced a transient rise in intracellular calcium in growing neurons 05 but a sustained rise in growing neurons B19. In stable-state (nong-rowing) cells A23187 evoked only a transient calcium rise. Both neuron-specific and state-specific differences in calcium homeostasis were dependent on extracellular sodium. Morphological studies also indicated that such differences in calcium-regulatory capacity can have profound consequences on the generation and degeneration of neuronal architecture.

The effects of midazolam on hippocampal dentate gyrus granule neurons from young and old Fischer 344 rats.

The effects of midazolam (3 nM) perfusion on the membrane and synaptic properties of dentate gyrus granule neurons were examined in hippocampal slices obtained from young adult (4-6 months) and old (24-26 months) Fischer 344 rats. In young neurons, midazolam perfusion resulted in a hyperpolarization of the resting membrane potential with no apparent change in the input resistance. Midazolam perfusion also produced a significant increase in the amplitude of the post-spike train afterhyperpolarization (AHP). In neurons obtained from old animals, midazolam perfusion also produced a hyperpolarization of the resting membrane potential but did not significantly change the AHP. These effects may result from altered calcium homeostasis in neurons of the aged brain, and suggest that at least some of the direct actions of benzodiazepines on mammalian central neurons are altered during aging.

Regulation of calcium homeostasis in sensory neurons by bradykinin

The nonapeptide bradykinin (BK) activates sensory neurons and stimulates the transmission of nociceptive information into the CNS. We investigated the effect of this peptide on rat dorsal root ganglion neurons (DRG) grown in vitro. BK stimulated the synthesis of inositol trisphosphate (IP3) and the breakdown of phosphatidylinositol bisphosphate, the synthesis of diacylglycerol, and the release of arachidonic acid from DRG cells. The release of IP3 and arachidonic acid was not inhibited by pretreatment of the cells with pertussis toxin. BK also mobilized intracellular Ca2+ stores in DRG cells as assessed by fura-2-based microfluorimetry. Two types of Ca2+ stores appeared to exist in DRG neurons. One type could be mobilized by caffeine (10(-2) M), and this effect could be blocked by ryanodine in a use-dependent manner. These stores occurred primarily in the cell soma and were virtually absent from cell processes. A second type of store could be mobilized by BK, presumably through the mediation of IP3. These latter stores were distributed equally between the cell soma and processes. Experiments with combinations of caffeine and BK suggested that the stores mobilized by these 2 agents may be separate entities. Both the caffeine and BK sensitive Ca2+ storage sites appeared to participate in buffering a Ca2+ load induced in DRG neurons by cell depolarization. The relevance of these observations to the mechanism of action of BK on sensory neurons is discussed.

Ethanol increases synaptosomal free calcium concentration

The effect of ethanol on synaptosomal free calcium concentration ([Ca 2+] i) and 45Ca 2+ uptake was studied in vitro. Synaptosomes were prepared from forebrains of adult rats and incubated in the presence of ethanol 50 500 mM. [Ca 2+] i determined by means of the Ca 2+-sensitive dye, fura-2, was increased by ethanol in polarized and depolarized synaptosomes, whereas 45Ca 2+ uptake was decreased. The results suggest that ethanol may influence neuronal calcium homeostasis by increasing rather than decreasing [Ca 2+] i.

Peroxidation of brain lipids following cyanide intoxication in mice

Lipid peroxidation of brain lipids as determined by the conjugated diene method was observed in mice following administration of sublethal doses of potassium cyanide (KCN). Conjugated diene production was dose- and time-dependent; 10 mg/kg KCN produced detectable levels of conjugated dienes at 30 min post cyanide, whereas, 15 mg/kg produced marked levels of conjugated dienes over a 10–60-min period after KCN. Pretreatment of mice with either diltiazem (600 μg/kg, i.v.) or allopurinol (25 mg/kg, i.v.) blocked the generation of conjugated dienes. These results suggest lipid peroxidation of neuronal membranes play a role in cyanide intoxication and this action is related to altered regulation of neuronal calcium homeostasis and activation of xanthine oxidase.

Drugs affecting calcium movements and the aging brain

Drugs acting on neuronal calcium homeostasis may potentially affect the aging brain, but the risk/benefit ratio of this approach should be carefully evaluated.

Neuronal calcium homeostasis

How do nerve cells regulate the level of free calcium ions in their cytoplasm? It appears that low resting levels must be maintained while changes sufficient to activate many intracellular processes must also be allowed. This article briefly explores some of the cellular mechanisms that could contribute to calcium homeostasis in neurones. If we are to conclude anything, it is that the regulation of cell calcium is a highly complex task, and understanding the process will certainly yield new insights into the normal physiology and the pathology of nerve cells.

Byssinosis among winders in the cotton industry.

The G2019S mutation in leucine-rich repeat kinase 2 (LRRK2) causes familial Parkinson’s disease (PD) and is also found in a subset of idiopathic cases. Prior studies in <i>Drosophila</i> and human induced pluripotent stem cell (iPSC)-derived dopamine neurons uncovered a pronounced effect of G2019S LRRK2 on mRNA translation. It was previously reported that G2019S LRRK2 promotes translation of mRNAs with complex 5′ untranslated region (UTR) secondary structure, resulting in increased expression of calcium channels and dysregulated calcium homeostasis in human dopamine neurons. Here, we show that dysregulated translation occurs in the brains of mammalian LRRK2 models <i>in vivo</i>. Through ribosome profiling studies of global translation, we observe that mRNAs with complex 5′UTR structure are also preferentially translated in the G2019S LRRK2-expressing mouse brain. Reporter assays suggest that this 5′UTR preference is independent of translation initiation factors. Conversely, translation of mRNAs with complex 5′UTR secondary structure is downregulated in LRRK2 knock-out (KO) mouse brain, indicating a robust link between LRRK2 kinase activity and translation of mRNA with complex 5′UTR structure. Further, substantia nigra pars compacta (SNpc) dopamine neurons in the G2019S LRRK2-expressing brain exhibit increased calcium influx, which is consistent with the previous report from human dopamine neurons. These results collectively suggest that LRRK2 plays a mechanistic role in translational regulation, and the G2019S mutation in LRRK2 causes translational defects leading to calcium dysregulation in the mammalian brain.