Intracellular Calcium Oscillations Research Articles

Intracellular calcium oscillations in articular chondrocytes induced by basic calcium phosphate crystals lead to cartilage degradation

Intracellular calcium oscillations in articular chondrocytes induced by basic calcium phosphate crystals lead to cartilage degradation

The effect of intracellular calcium oscillations on fluid secretion in airway epithelium

Airway epithelium has been shown to elicit fluid secretion after a rise in intracellular calcium. This rise in intracellular calcium has been shown to display complex oscillations in many species after the binding of particular agonists to extracellular receptors.Fluid secreted by the airway epithelium is used to maintain the depth of the periciliary liquid (PCL) above the apical membrane of the epithelial cells lining the bronchial airways. Previous mathematical models have been published which separately consider the electrophysiology involved in regulating periciliary liquid depth, and the transmission of intracellular calcium waves in airway epithelial tissue. In this paper we present a mathematical model that combines these previous models and allows the effect of oscillations in intracellular calcium on fluid secretion by airway epithelial cells to be investigated. We show that an oscillatory calcium response produces different fluid secretion properties to that elicited by a tonic rise in intracellular calcium. These differences are shown to be due to saturation of the Ca2+ activated ion channels.

Dynamics of intracellular [formula omitted] oscillations in the presence of multisite [formula omitted]-binding proteins

We study the dynamics of intracellular calcium oscillations in the presence of proteins that bind calcium on multiple sites and that are generally believed to act as passive calcium buffers in cells. These multisite calcium-binding proteins set a sharp threshold for calcium oscillations, and calcium oscillations stop at high concentrations of calcium-binding proteins. However even in these adverse conditions, internal noise, which shows up spontaneously in cells in the process of calcium wave formation, can lead to self-oscillations. This produces oscillatory behaviors strikingly similar to those observed in real cells. In addition, for given intracellular concentrations of both calcium and calcium-binding proteins the regularity of these oscillations changes and reaches a maximum as a function of the noise variance, and we find that the overall system dynamics displays coherence resonance. Thus it turns out that the calcium-binding proteins can have an important and non-trivial regularizing role.

Neuropeptide Y Directly Inhibits Neuronal Activity in a Subpopulation of Gonadotropin-Releasing Hormone-1 Neurons via Y1 Receptors

Neuropeptide Y (NPY), a member of the pancreatic polypeptide family, is an orexigenic hormone. GnRH-1 neurons express NPY receptors. This suggests a direct link between metabolic function and reproduction. However, the effect of NPY on GnRH-1 cells has been variable, dependent on metabolic and reproductive status of the animal. This study circumvents these issues by examining the role of NPY on GnRH-1 neuronal activity in an explant model that is based on the extra-central nervous system origin of GnRH-1 neurons. These prenatal GnRH-1 neurons express many receptors found in GnRH-1 neurons in the brain and use similar transduction pathways. In addition, these GnRH-1 cells exhibit spontaneous and ligand-induced oscillations in intracellular calcium as well as pulsatile calcium-controlled GnRH-1 release. Single-cell PCR determined that prenatal GnRH-1 neurons express the G protein-coupled Y1 receptor (Y1R). To address the influence of NPY on GnRH-1 neuronal activity, calcium imaging was used to monitor individual and population dynamics. NPY treatment, mimicked with Y1R agonist, significantly decreased the number of calcium peaks per minute in GnRH-1 neurons and was prevented by a Y1R antagonist. Pertussis toxin blocked the effect of NPY on GnRH-1 neuronal activity, indicating the coupling of Y1R to inhibitory G protein. The NPY-induced inhibition was independent of the adenylate cyclase pathway but mediated by the activation of G protein-coupled inwardly rectifying potassium channels. These results indicate that at an early developmental stage, GnRH-1 neuronal activity can be directly inhibited by NPY via its Y1R.

Growth-dependent modulation of capacitative calcium entry in normal rat kidney fibroblasts

Normal rat kidney (NRK) fibroblasts have electrophysiological properties and intracellular calcium dynamics that are dependent upon their growth stage. In the present study we show that this differential behavior coincides with a differential calcium entry that can be either capacitative or non-capacitative. Confluent cells made quiescent by serum deprivation, which have a stable membrane potential near − 70 mV and do not show spontaneous intracellular calcium oscillations, primarily exhibit the capacitative mechanism for calcium entry, also called store-operated calcium entry (SOCE). When the quiescent cells are grown to density-arrest in the presence of EGF as the sole polypeptide growth factor, these cells characteristically fire spontaneously repetitive calcium action potentials, which propagate throughout the whole monolayer and are accompanied by intracellular calcium transients. These density-arrested cells appear to exhibit in addition to SOCE also receptor-operated calcium entry (ROCE) as a mechanism for calcium entry. Furthermore we show that, in contrast to earlier studies, the employed SOCs and ROCs are permeable for both calcium and strontium ions. We examined the expression of the canonical transient receptor potential channels (Trpcs) that may be involved in SOCE and ROCE. We show that NRK fibroblasts express the genes encoding Trpc1, Trpc5 and Trpc6, and that the levels of their expression are dependent upon the growth stage of the cells. In addition we examined the growth stage dependent expression of the genes encoding Orai1 and Stim1, two proteins that have recently been shown to be involved in SOCE. Our results suggest that the differential expression of Trpc5, Trpc6, Orai1 and Stim1 in quiescent and density-arrested NRK fibroblasts is responsible for the difference in regulation of calcium entry between these cells. Finally, we show that inhibition or potentiation of SOCE and ROCE by pharmacological agents has profound effects on calcium dynamics in NRK fibroblasts.

Calcium Signaling in Astrocytes: Modeling Fura-2AM Measurements

Event Abstract Back to Event Calcium Signaling in Astrocytes: Modeling Fura-2AM Measurements Eeva Toivari1, Tiina Manninen1*, Amit K. Nahata2, Tuula O. Jalonen3 and Marja-Leena Linne1 1 Tampere University of Technology, Finland 2 Kidney Care Center at DCI, United States 3 School of Medicine, St. Georges University, Department of Physiology and Neuroscience, Grenada Purpose: In addition to wet lab and clinical studies, mathematical models can be used to better understand and verify the hypothesis concerning complex molecular level interactions, including the role of intracellular calcium stores such as endoplasmic reticulum, in cellular functions. Ionic equilibrium in astrocytes can be disturbed by transmitters, for example by serotonin and Alzheimer's disease related amyloid plaques forming amyloid-ß peptides (Aß). We studied the effects of small amounts of Aß fragments on the neurotransmitter-induced calcium signals in astrocytes by doing Fura-2-acetoxymethyl ester (Fura-2AM) measurements and computer modeling based on calcium-induced kinetic reactions. Method: Fura-2AM measurements were done to study the effects of transmitters, such as serotonin and glutamate, on the cytosolic concentration of calcium in astrocytes separately and together with neurotoxic Aß25-35. Fura-2AM is a membrane penetrating derivative of the radiometric calcium indicator Fura-2 used in biochemistry to measure intracellular calcium concentrations by fluorescence. Aß25-35 is a synthetic derivative of the longer peptide Aß42 which predominates in the neuritic plaques. A computational model, introduced by Di Garbo et al. (2007), was adjusted to mimic the calcium signals measured with the calcium imaging technique. The model includes kinetic reaction equations, for example, the effect of both metabotropic and ionotropic receptors, the flux of calcium from/to extracellular matrix, the pumping of calcium from cytosol to the endoplasmic reticulum and the leak back to cytosol, and the release of calcium from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptors. Results: Though serotonin and glutamate have earlier been shown to induce calcium release in astrocytes (Jalonen et al. 1997, Kimelberg et al. 1997), it is shown in this study how serotonin and Aß25-35, when added together, clearly increase the amplitudes of the calcium signal. Thus, even small amounts of neurotoxic Aß25-35 can have a severe effect on the intracellular ionic equilibrium. In the modeling part of this study, different experimental setups were computationally simulated using different values of the model parameters and/or different inputs. The model presented by Di Garbo et al. (2007) was found to sufficiently explain the results measured by us using the Fura-2AM technique. For example, phenomena related to unfilled intracellular calcium stores were observed both by calcium imaging and computer simulations. Thus, model simulations support the hypothesis about the importance of intracellular calcium stores, such as endoplasmic reticulum, to calcium signaling in astrocytes. Conclusions: We conclude that the experimental results on astrocytic calcium oscillations can be reproduced with the computational model originally proposed by Di Garbo et al. (2007). Modeling the mechanisms of intracellular calcium oscillations in astrocytes is important, as astrocytes have an essential role in regulating the central nervous system microenvironment.

Equine phospholipase C zeta (PLCζ) supports intracellular calcium oscillations in mouse oocytes

Equine phospholipase C zeta (PLCζ) supports intracellular calcium oscillations in mouse oocytes

Mixed-integer non-linear optimal control in systems biology and biotechnology: numerical methods and a software toolbox

Here we consider the problem of optimal manipulation of biological or biotechno-logical systems, formulated as a class of mixed-integer optimal control problems. We describe the current state of the art regarding the numerical solution of these problems, and a software implementation developed in our group (DOTcvp toolbox, based on Matlab).DOTcvp combines the control vector parameterization approach with a number of local deterministic and global stochastic and hybrid (mixed-integer) non-linear programming solvers and suitable dynamic process simulation methods so as to cover the solution of a wide class of problems. The performance of DOTcvp is illustrated considering representative set of benchmark problems, including the problem of drug displacement in a patient, the optimal operation of a fed-batch bioreactor, and the optimal control of intracellular calcium oscillations. The DOTcvp toolbox is freely available to academic users.

Glucose Metabolism, Islet Architecture, and Genetic Homogeneity in Imprinting of [Ca2+]i and Insulin Rhythms in Mouse Islets

We reported previously that islets isolated from individual, outbred Swiss-Webster mice displayed oscillations in intracellular calcium ([Ca2+]i) that varied little between islets of a single mouse but considerably between mice, a phenomenon we termed “islet imprinting.” We have now confirmed and extended these findings in several respects. First, imprinting occurs in both inbred (C57BL/6J) as well as outbred mouse strains (Swiss-Webster; CD1). Second, imprinting was observed in NAD(P)H oscillations, indicating a metabolic component. Further, short-term exposure to a glucose-free solution, which transiently silenced [Ca2+]i oscillations, reset the oscillatory patterns to a higher frequency. This suggests a key role for glucose metabolism in maintaining imprinting, as transiently suppressing the oscillations with diazoxide, a KATP-channel opener that blocks [Ca2+]i influx downstream of glucose metabolism, did not change the imprinted patterns. Third, imprinting was not as readily observed at the level of single beta cells, as the [Ca2+]i oscillations of single cells isolated from imprinted islets exhibited highly variable, and typically slower [Ca2+]i oscillations. Lastly, to test whether the imprinted [Ca2+]i patterns were of functional significance, a novel microchip platform was used to monitor insulin release from multiple islets in real time. Insulin release patterns correlated closely with [Ca2+]i oscillations and showed significant mouse-to-mouse differences, indicating imprinting. These results indicate that islet imprinting is a general feature of islets and is likely to be of physiological significance. While islet imprinting did not depend on the genetic background of the mice, glucose metabolism and intact islet architecture may be important for the imprinting phenomenon.

76 DEVELOPMENTAL CAPABILITY OF TRANSGENIC NUCLEAR-TRANSFERRED PIG EMBRYOS PRODUCED USING THE NOVEL METHOD OF PSEUDOPHYSIOLOGICAL ACTIVATION

The physicochemical stimuli, which are commonly used for artificial activation of porcine nuclear-transferred (NT) oocytes, can affect detrimentally or cytotoxically the clonal cybrids and thereby inhibit the development or decrease the quality of cloned embryos. Therefore, we have recently developed a novel method of pseudophysiological transcomplementary (transcytoplasmic) activation to stimulate the developmental program of porcine oocytes reconstructed by somatic cell nuclear transfer. The mechanism underlying this original technique of activation is transcytoplasmic influx of sperm-derived proteins triggering intracellular calcium oscillations, which is mediated via heterologous (rabbit) zygote-descended cytoplasts. The purpose of our study was to estimate the in vitro developmental competences of porcine transgenic cloned embryos following pseudophysiological activation of oocytes receiving pWAPhGH-GFPBsd gene construct-nucleofected fetal fibroblast cell nuclei. In the cloning procedure, IVM pig oocytes were used as recipient cells for cell nuclei of positively selected transgenic fibroblast cells. The reconstruction of enucleated oocytes was performed by intracytoplasmic injection of either the somatic cell-derived karyoplast or whole tiny nuclear donor cell. The activation of porcine NT oocytes was achieved by electrofusion of them with the xenogeneic cytoplasts isolated from in vivo-derived rabbit zygotes (i.e. with the so-called zygoplasts), which led to the formation of triple xenocytoplasmic hybrids (xenocybrids). The rabbit zygotes had been flushed postmortem from the separated oviducts of superovulated postpubertal female donors 18 to 20 hafter administration of hCG and copulation. Single rabbit zygote-descended cytoplasts were inserted into the perivitelline space of previously reconstructed pig oocytes. The resulting zygoplast-NT oocyte couplets underwent fusion, which was induced by generation of 2 successive DC pulses of 1.2 kV cm-1 for 60 μs. The electrofusion medium consisted of 0.3 M Ca2+-deprived mannitol supplemented with 0.1 mM MgSO4 and 0.2 mg mL-1 fatty-acid-free BSA. The transcytoplasmically activated xenocybrids were cultured in vitro for 6 to 7 days up to morula/blastocyst stages. A total of 183/207 (88.4%) oocytes reconstructed with nucleofected fibroblast cell nuclei were successfully fused with zygoplasts. Out of 183 cultured NT embryos, 138 (75.4%) were cleaved. The rates of transgenic NT embryos that reached the morula and blastocyst stages yielded 106/183 (57.9%) and 65/183 (35.5%), respectively. In conclusion, the original method of pseudophysiological activation of porcine NT oocytes turned out to be relatively efficient, which has been confirmed by the high percentages of pWAPhGH-GFPBsd transgenic embryos developing in vitro to morula and blastocyst stages.

Altered Calcium Dynamics Mediates P19-Derived Neuron-Like Cell Responses to Millimeter-Wave Radiation

Intracellular calcium oscillations have long been recognized as a principal mediator of many vital cellular activities. Furthermore, Ca(2+) dynamics can be modulated by external physical cues, including electromagnetic fields. While cellular responses to low-frequency electric fields have been established, the possible non-thermal effects of millimeter-wave (MMW) radiation are still a subject of discussion and debate. We used mouse embryonic stem cell-derived neuronal cells and a custom-built 94 GHz applicator to examine in real time the altered Ca(2+) oscillations associated with MMW stimulation. MMW irradiation at 18.6 kW/m(2) nominal power density significantly increased the Ca(2+) spiking frequency in the cells exhibiting Ca(2+) activity. The N-type calcium channels, phospholipase C enzyme, and actin cytoskeleton appear to be involved in mediating increased Ca(2+) spiking. Reorganization of the actin microfilaments by a 94 GHz field seems to play a crucial role in modulating not only Ca(2+) activity but also cell biomechanics. Many but not all observed cellular responses to MMW were similar to thermally induced effects. For example, cell exposure to a 94 GHz field induced nitric oxide production in some morphologically distinct neuronal cells that could not be reproduced by thermal heating of the cells up to 42 degrees C. The highest observed average temperature rise in the MMW exposure chamber was approximately 8 degrees C above the room temperature, with possible complex non-uniform microscopic distribution of heating rates at the cell level. Our findings may be useful to establish quantitative molecular benchmarks for elucidation of nociception mechanisms and evaluation of potential adverse bioeffects associated with MMW exposure. Moreover, control of Ca(2+) dynamics by MMW stimulation may offer new tools for regulation of Ca(2+)-dependent cellular and molecular activities, for example, in tissue engineering applications.

Low doses of hydrogen peroxide impair glucose-stimulated insulin secretion via inhibition of glucose metabolism and intracellular calcium oscillations

The inhibitory effect of hydrogen peroxide (H 2O 2) on glucose-stimulated insulin secretion was previously reported. However, the precise mechanism involved was not systematically investigated. In this study, the effects of low concentrations of H 2O 2 (5-10 μmol/L) on glucose metabolism, intracellular calcium ([Ca 2+] i) oscillations, and dynamic insulin secretion in rat pancreatic islets were investigated. Low concentrations of H 2O 2 impaired insulin secretion in the presence of high glucose levels (16.7 mmol/L). This phenomenon was observed already after 2 minutes of exposure to H 2O 2. Glucose oxidation and the amplitude of [Ca 2+] i oscillations were dose-dependently suppressed by H 2O 2. These findings indicate that low concentrations of H 2O 2 reduce insulin secretion in the presence of high glucose levels via inhibition of glucose metabolism and consequent impairment in [Ca 2+] i handling.

Calcium oscillations in the olfactory nonsensory cells of the goldfish, Carassius auratus

Background The olfactory nonsensory cells contribute to the maintenance of normal functions of the olfactory epithelium (OE). Specifically, the ciliated nonsensory cells of teleosts play important roles in the odorant detection by OE in aqueous environment. Their cilia show strong beating activities and cause water flow at the OE surface, making the detection of odorants by OE more efficient. Because intracellular Ca 2+ level has been reported to play an important role in ciliary beating, the ciliary beating activity may be regulated by intracellular Ca 2+ dynamics of these ciliated nonsensory cells. Methods We performed Ca 2+ imaging experiments to analyze the Ca 2+ dynamics in acutely dissociated OE cells of the goldfish. Furthermore, we examined the contribution of the Ca 2+ dynamics to the ciliary beating frequency (CBF) at the surface of the intact OE. Results Olfactory nonsensory cells showed both spontaneous intracellular Ca 2+ oscillations and propagating intercellular Ca 2+ waves. Application of 2-aminoethoxydiphenylborate (2-APB), which antagonizes IP 3-induced Ca 2+ release from intracellular stores suppressed these Ca 2+ oscillations. Furthermore, 2-APB application to the intact OE lamellae resulted in the decrease of CBF at the surface of the OE. Conclusions These results indicate that spontaneous intracellular calcium oscillations persistently up-regulate the ciliary beating at the surface of the OE in teleosts. General significance Ciliary beating activity at the surface of OE can be regulated by the Ca 2+ dynamics of olfactory nonsensory cells. Because this ciliary movement causes inflow of external fluid into the nostril, this regulation is suggested to influence the efficiency of odorant detection by OE.

Physiology, Injury, and Recovery of Interstitial Cells of Cajal: Basic and Clinical Science

In the last 15 years, our understanding of the cellular basis of gastrointestinal function has been altered irreversibly by the discovery that normal gastrointestinal (GI) motility requires interstitial cells of Cajal (ICC). Research in this relatively short time period has modified our original concept that the core unit that controls motility is made up of nerves and smooth muscle, to one that now includes ICC. This concept has now expanded to beyond the GI tract, suggesting that it may be a fundamental property of the regulation of smooth muscle function that requires rhythmic contraction. ICC are distributed throughout the GI tract, have important functions in the control of GI motility, and are often abnormal in diseased states. Recently, significant steps forward have been made in our understanding of the physiology of ICC as well as mechanisms of injury and recovery. These advances are the focus of this review. The Physiology of ICC Unique motor patterns are intrinsic to every organ of the GI tract, which suit their functions related to mixing, absorption, and anally directed movement. The ICC are an integral part of the control of these motor activities. The distribution of ICC throughout the musculature is associated with nerve structures. Myenteric pacemaker ICC surround the myenteric or Auerbach’s plexus and intramuscular ICC are associated with nerve varicosities throughout the muscle layers (Figures 1 and 2). Other subpopulations of ICC are associated with nonganglionated plexuses of nerve varicosities at the inner borders of the circular muscle layers in the intestine and colon (Figures 1 and 2). The best understood function is that of pacemaker activity in the stomach and small intestine where the ICC generate a periodic depolarization at a characteristic frequency in each of these organs that is called the slow wave or pacemaker activity.

Minimal models of electric potential oscillations in non-excitable membranes

Sustained oscillations in the membrane potential have been observed in a variety of cellular and subcellular systems, including several types of non-excitable cells and mitochondria. For the plasma membrane, these electrical oscillations have frequently been related to oscillations in intracellular calcium. For the inner mitochondrial membrane, in several cases the electrical oscillations have been attributed to modifications in calcium dynamics. As an alternative, some authors have suggested that the sustained oscillations in the mitochondrial membrane potential induced by some metabolic intermediates depends on the direct effect of internal protons on proton conductance. Most theoretical models developed to interpret oscillations in the membrane potential integrate several transport and biochemical processes. Here we evaluate whether three simple dynamic models may constitute plausible representations of electric oscillations in non-excitable membranes. The basic mechanism considered in the derivation of the models is based upon evidence obtained by Hattori et al. for mitochondria and assumes that an ionic species (i.e., the proton) is transported via passive and active transport systems between an external and an internal compartment and that the ion affects the kinetic properties of transport by feedback regulation. The membrane potential is incorporated via its effects on kinetic properties. The dynamic properties of two of the models enable us to conclude that they may represent alternatives enabling description of the generation of electrical oscillations in membranes that depend on the transport of a single ionic species.

STIM1 Is a Calcium Sensor Specialized for Digital Signaling

When cells are activated by calcium-mobilizing agonists at low, physiological concentrations, the resulting calcium signals generally take the form of repetitive regenerative discharges of stored calcium, termed calcium oscillations [1]. These intracellular calcium oscillations have long fascinated biologists as a mode of digitized intracellular signaling. Recent work has highlighted the role of calcium influx as an essential component of calcium oscillations [2]. This influx occurs through a process known as store-operated calcium entry, which is initiated by calcium sensor proteins, STIM1 and STIM2, in the endoplasmic reticulum [3]. STIM2 is activated by changes in endoplasmic reticulum calcium near the resting level, whereas a threshold of calcium depletion is required for STIM1 activation [4]. Here we show that, surprisingly, it is STIM1 and not STIM2 that is exclusively involved in calcium entry during calcium oscillations. The implication is that each oscillation produces a transient drop in endoplasmic reticulum calcium and that this drop is sufficient to transiently activate STIM1. This transient activation of STIM1 can be observed in some cells by total internal reflection fluorescence microscopy. This arrangement nicely provides a clearly defined and unambiguous signaling system, translating a digital calcium release signal into calcium influx that can signal to downstream effectors.

Special issue on neuron–glia interactions

Special issue on neuron–glia interactions

Fertility potential of mouse oocytes revealed by cytosolic calcium after cryopreservation and in vitro maturation

OBJECTIVE: To test whether cryopreservation of mouse oocytes at an intermediate stage of maturation in vitro is optimal for developmental competence. DESIGN: Germinal vesicle (GV) oocytes were matured in vitro to metaphase II (MII) with or without cryopreservation at different stages. At MII they were activated by intracytoplasmic sperm injection (ICSI) and intracellular calcium oscillations were monitored to predict developmental competence. MATERIALS AND METHODS: 6 week-old B6D2F1 mice were primed with PMSG and oocytes harvested for cryopreservation in 1.5M 1,2-propanediol at GV, pro-metaphase I (GVBD) or MII stages, or used as fresh controls. Oocytes were matured to the MII stage after thawing, and ICSI was performed with B6D2F1 sperm using a Piezo drill. Calcium oscillations were subsequently measured in oocytes loaded with Fura-2/AM using a fluorescence microscope and InCyt 2 software to measure fluorescence ratios at 340/380 nm and determine intracellular calcium. The data were analyzed by non-parametric statistical tests and ANOVA. RESULTS: There were no significant differences in survival between the three stages at cryopreservation (84-94%). Fresh oocytes exhibited normal calcium spikes every 15-20 min post-fertilization lasting 3-4 hr. After cryopreservation at GV or GVBD stages, maturation to MII and ICSI, persistent calcium oscillations were induced similar to fresh oocytes, but they were truncated or absent in oocytes cryopreserved at the MII stage. CONCLUSIONS: Cryopreservation of oocytes prior to the MII stage appeared to improve developmental potential as indicated by their ability to support normal intracellular calcium oscillations. There was no reduction of survival after thawing. Since calcium signaling is essential for successful fertilization and an excellent indicator of competence, there may be an unexpected advantage of banking oocytes at GV or GVBD stages instead of MII, perhaps from a longer cellular recovery time after the stress of cryopreservation.

Model for Influences of Magnetic Fields on Intracellular Calcium Oscillations

Based on the model of the two calcium stores developed by Goldbeter, the influence of external magnetic field on the calcium concentration has been discussed. We believe that the cell membrane is a major site of interaction for extremely-low-frequency (ELF) electromagnetic fields, and the permeability of ions can be changed with the changing electromagnetic fields. It is shown that magnetic field initiates intracellular calcium oscillation with a threshold in flux density, and that the calcium oscillations do not occur if the density of magnetic field is below the threshold. The results of theoretical calculation are consistent with that of the experiment. The intracellular free calcium concentrations of different cells exposed to the same magnetic fields are different from each other. It is indicated that the different behaviors such as oscillation, rise and invariability of calcium concentration are associated with the sort of cells.

Activation of Phosphatidylinositol-Linked D1-Like Receptor Modulates FGF-2 Expression in Astrocytes via IP3-Dependent Ca2+ Signaling

Fibroblast growth factor-2 (FGF-2) is predominantly synthesized and secreted by astrocytes in adult brain. Our previous study showed that activation of classical dopamine receptor D(1) or D(2) elicits FGF-2 biosynthesis and secretion in astrocytes. Here, we report that astrocytic FGF-2 expression is also regulated by phosphatidylinositol (PI)-linked D(1)-like receptor. SKF83959, a selective PI-linked D(1)-like receptor agonist, upregulates the levels of FGF-2 protein in striatal astrocyte cultures in classical dopamine D(1) and D(2) receptor-independent manner. The conditional medium derived from SKF83959-activated astrocytes promoted the number of TH(+) neurons in vitro. Treatment of astrocytes with SKF83959 increased intracellular calcium in two phases. Inhibition of intracellular calcium oscillation by inositol 1,4,5-triphosphate (IP3) inhibitors blocked the SKF83959-induced increase in FGF-2 expression. Moreover, intraperitoneal administration of SKF83959 reversed l-methyl-4-phenyl-l,2,3,6-tetrahydropypridine (MPTP)-induced reduction in FGF-2 expression in both the striatum and ventral midbrain and resulted in marked protection of dopaminergic neurons from MPTP-induced neurotoxicity. These results indicate that IP3/Ca(2+)/calmodulin-dependent protein kinase is an uncharted intracellular signaling pathway that is crucial for the regulation of FGF-2 synthesis in astrocytes. PI-linked D(1)-like receptor plays an important role in the regulation of astrocytic FGF-2 expression and neuroprotection which may provide a potential target for the drug discovery in Parkinson's disease.