Role of Ca2(+)-ATPases in regulation of cellular Ca2+ signalling, as studied with the selective microsomal Ca2(+)-ATPase inhibitor, thapsigargin

Age-related changes in P2Y receptor signalling in mouse cochlear supporting cells

Our sense of hearing depends on the function of a specialised class of sensory cells, the hair cells, which are found in the organ of Corti of the mammalian cochlea. The unique physiological environment in which these cells operate is maintained by a syncitium of non-sensory supporting cells, which are crucial for regulating cochlear physiology and metabolic homeostasis. Despite their importance for cochlear function, the role of these supporting cells in age-related hearing loss, the most common sensory deficit in the elderly, is poorly understood. Here, we investigated the age-related changes in the expression and function of metabotropic purinergic receptors (P2Y1 , P2Y2 and P2Y4 ) in the supporting cells of the cochlear apical coil. Purinergic signalling in supporting cells is crucial during the development of the organ of Corti and purinergic receptors are known to undergo changes in expression during ageing in several tissues. Immunolabelling and Ca2+ imaging experiments revealed a downregulation of P2Y receptor expression and a decrease of purinergic-mediated calcium responses after early postnatal stages in the supporting cells. An upregulation of P2Y receptor expression was observed in the aged cochlea when compared to 1 month-old adults. The aged mice also had significantly larger calcium responses and displayed calcium oscillations during prolonged agonist applications. We conclude that supporting cells in the aged cochlea upregulate P2Y2 and P2Y4 receptors and display purinergic-induced Ca2+ responses that mimic those observed during pre-hearing stages of development, possibly aimed at limiting or preventing further damage to the sensory epithelium. KEY POINTS: Age-related hearing loss is associated with lower hearing sensitivity and decreased ability to understand speech. We investigated age-related changes in the expression and function of metabotropic purinergic (P2Y) receptors in cochlear non-sensory supporting cells of mice displaying early-onset (C57BL/6N) and late-onset (C3H/HeJ) hearing loss. The expression of P2Y1 , P2Y2 and P2Y4 receptors in the supporting cells decreased during cochlear maturation, but that of P2Y2 and P2Y4 was upregulated in the aged cochlea. P2Y2 and P2Y4 receptors were primarily responsible for the ATP-induced Ca2+ responses in the supporting cells. The degree of purinergic expression upregulation in aged supporting cells mirrored hearing loss progression in the different mouse strains. We propose that the upregulation of purinergic-mediated signalling in the aged cochlea is subsequent to age-related changes in the hair cells and may act as a protective mechanism to limit or to avoid further damage to the sensory epithelium.

The UPR sensor IRE1α and the adenovirus E3-19K glycoprotein sustain persistent and lytic infections

Persistent viruses cause chronic disease, and threaten the lives of immunosuppressed individuals. Here, we elucidate a mechanism supporting the persistence of human adenovirus (AdV), a virus that can kill immunosuppressed patients. Cell biological analyses, genetics and chemical interference demonstrate that one of five AdV membrane proteins, the E3-19K glycoprotein specifically triggers the unfolded protein response (UPR) sensor IRE1α in the endoplasmic reticulum (ER), but not other UPR sensors, such as protein kinase R-like ER kinase (PERK) and activating transcription factor 6 (ATF6). The E3-19K lumenal domain activates the IRE1α nuclease, which initiates mRNA splicing of X-box binding protein-1 (XBP1). XBP1s binds to the viral E1A-enhancer/promoter sequence, and boosts E1A transcription, E3-19K levels and lytic infection. Inhibition of IRE1α nuclease interrupts the five components feedforward loop, E1A, E3-19K, IRE1α, XBP1s, E1A enhancer/promoter. This loop sustains persistent infection in the presence of the immune activator interferon, and lytic infection in the absence of interferon.

Adenovirus (AdV) can cause persistent infections, but underlying mechanisms are poorly understood. Here, Prasad et al. show that the AdV glycoprotein E3-19K activates the unfolded protein response sensor IRE1α, and that this triggers a feedforward loop that sustains persistent infection in the presence of interferon.

Age attenuates the T-type CaV 3.2-RyR axis in vascular smooth muscle

Caveolae position Ca_V3.2 (T‐type Ca²⁺ channel encoded by the α‐3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca²⁺ influx to trigger Ca²⁺ sparks and large‐conductance Ca²⁺‐activated K⁺ channel feedback in vascular smooth muscle. We hypothesize that this mechanism of Ca²⁺ spark generation is affected by age. Using smooth muscle cells (VSMCs) from mouse mesenteric arteries, we found that both Ca_v3.2 channel inhibition by Ni²⁺ (50 µM) and caveolae disruption by methyl‐ß‐cyclodextrin or genetic abolition of Eps15 homology domain‐containing protein (EHD2) inhibited Ca²⁺ sparks in cells from young (4 months) but not old (12 months) mice. In accordance, expression of Ca_v3.2 channel was higher in mesenteric arteries from young than old mice. Similar effects were observed for caveolae density. Using SMAKO Ca_v1.2^−/− mice, caffeine (RyR activator) and thapsigargin (Ca²⁺ transport ATPase inhibitor), we found that sufficient SR Ca²⁺ load is a prerequisite for the Ca_V3.2‐RyR axis to generate Ca²⁺ sparks. We identified a fraction of Ca²⁺ sparks in aged VSMCs, which is sensitive to the TRP channel blocker Gd³⁺ (100 µM), but insensitive to Ca_V1.2 and Ca_V3.2 channel blockade. Our data demonstrate that the VSMC Ca_V3.2‐RyR axis is down‐regulated by aging. This defective Ca_V3.2‐RyR coupling is counterbalanced by a Gd³⁺ sensitive Ca²⁺ pathway providing compensatory Ca²⁺ influx for triggering Ca²⁺ sparks in aged VSMCs.

Overview of the mammalian ADP-ribosyl-transferases clostridia toxin-like (ARTCs) family

Mono-ADP-ribosylation is a reversible post-translational protein modification that modulates the function of proteins involved in different cellular processes, including signal transduction, protein transport, transcription, cell cycle regulation, DNA repair and apoptosis. In mammals, mono-ADP-ribosylation is mainly catalyzed by members of two different classes of enzymes: ARTCs and ARTDs. The human ARTC family is composed of four structurally related ecto-mono-ARTs, expressed at the cell surface or secreted into the extracellular compartment that are either active mono-ARTs (hARTC1, hARTC5) or inactive proteins (hARTC3, hARTC4). The human ARTD enzyme family consists of 17 multidomain proteins that can be divided on the basis of their catalytic activity into polymerases (ARTD1-6), mono-ART (ARTD7-17), and the inactive ARTD13. In recent years, ADP-ribosylation was intensively studied, and research was dominated by studies focusing on the role of this modification and its implication on various cellular processes. The aim of this review is to provide a general overview of the ARTC enzymes. In the following sections, we will report the mono-ADP-ribosylation reactions that are catalysed by the active ARTC enzymes, with a particular focus on hARTC1 that recently has been intensively studied with the discovery of new targets and functions.

ATP as a Messenger in Astrocyte-Neuronal Communication

Astrocytes are activated during both excitatory and inhibitory synaptic transmission and respond with intracellular Ca2+i elevations. Ca2+i oscillations and waves in astrocytes now appear to represent the glial arm of a dynamic neuronal-glial signaling process. Advances within the last year have shown that stimuli that elevate Ca2+i in astrocytes have the potential to modulate synaptic function. Recent studies have shown that astrocytic calcium waves, initially believed to depend on the integrity of functional gap junction channels for the passage of intercellular signals, are actually mediated by release of ATP and subsequent activation of purinergic receptors on neighboring cells. ATP release is in turn regulated by the expression of gap junction proteins, establishing a novel dimension between gap junctions and extracellular-mediated signaling events. The role of ATP and its breakdown product, adenosine, on synaptic transmission are discussed.

Cadmium Induces Apoptosis in Freshwater Crab Sinopotamon henanense through Activating Calcium Signal Transduction Pathway

Calcium ion (Ca²⁺) is one of the key intracellular signals, which is implicated in the regulation of cell functions such as impregnation, cell proliferation, differentiation and death. Cadmium (Cd) is a toxic environmental pollutant that can disturb cell functions and even lead to cell death. Recently, we have found that Cd induced apoptosis in gill cells of the freshwater crab Sinopotamon henanense via caspase activation. In the present study, we further investigated the role of calcium signaling in the Cd-induced apoptosis in the animals. Our data showed that Cd triggered gill cell apoptosis which is evidenced by apoptotic DNA fragmentation, activations of caspases-3, -8 and -9 and the presence of apoptotic morphological features. Moreover, Cd elevated the intracellular concentration of Ca²⁺, the protein concentration of calmodulin (CaM) and the activity of Ca²⁺-ATPase in the gill cells of the crabs. Pretreatment of the animals with ethylene glycol-bis-(b-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA), Ca²⁺ chelator, inhibited Cd-induced activation of caspases-3, -8 and -9 as well as blocked the Cd-triggered apoptotic DNA fragmentation. The apoptotic morphological features were no longer observed in gill cells pretreated with the Ca²⁺ signaling inhibitors before Cd treatment. Our results indicate that Cd evokes gill cell apoptosis through activating Ca²⁺-CaM signaling transduction pathway.

G-protein-coupled receptor controls steroid hormone signaling in cell membrane

G-protein-coupled receptors (GPCRs) are involved in animal steroid hormone signaling, but their mechanism is unclear. In this research, we report that a GPCR called ErGPCR-2 controls steroid hormone 20-hydroxyecdysone (20E) signaling in the cell membrane of the lepidopteran insect Helicoverpa armigera. ErGPCR-2 was highly expressed during molting and metamorphosis. 20E, via ErGPCR-2, regulated rapid intracellular calcium increase, protein phosphorylation, gene transcription, and insect metamorphosis. ErGPCR-2 was located in the cell surface and was internalized by 20E induction. GPCR kinase 2 participated in 20E-induced ErGPCR-2 phosphorylation and internalization. The internalized ErGPCR-2 was degraded by proteases to desensitize 20E signaling. ErGPCR-2 knockdown suppressed the entrance of 20E analog [(3)H] ponasterone A ([(3)H]Pon A) into the cells. ErGPCR-2 overexpression or blocking of ErGPCR-2 internalization increased the entrance of [(3)H]Pon A into the cells. However, ErGPCR-2 did not bind to [(3)H]Pon A. Results suggest that ErGPCR-2 transmits steroid hormone 20E signaling and controls 20E entrance into cells in the cell membrane.

ARTC1-mediated ADP-ribosylation of GRP78/BiP: a new player in endoplasmic-reticulum stress responses

Protein mono-ADP-ribosylation is a reversible post-translational modification of cellular proteins. This scheme of amino-acid modification is used not only by bacterial toxins to attack host cells, but also by endogenous ADP-ribosyltransferases (ARTs) in mammalian cells. These latter ARTs include members of three different families of proteins: the well characterised arginine-specific ecto-enzymes (ARTCs), two sirtuins, and some members of the poly(ADP-ribose) polymerase (PARP/ARTD) family. In the present study, we demonstrate that human ARTC1 is localised to the endoplasmic reticulum (ER), in contrast to the previously characterised ARTC proteins, which are typical GPI-anchored ecto-enzymes. Moreover, using the "macro domain" cognitive binding module to identify ADP-ribosylated proteins, we show here that the ER luminal chaperone GRP78/BiP (glucose-regulated protein of 78 kDa/immunoglobulin heavy-chain-binding protein) is a cellular target of human ARTC1 and hamster ARTC2. We further developed a procedure to visualise ADP-ribosylated proteins using immunofluorescence. With this approach, in cells overexpressing ARTC1, we detected staining of the ER that co-localises with GRP78/BiP, thus confirming that this modification occurs in living cells. In line with the key role of GRP78/BiP in the ER stress response system, we provide evidence here that ARTC1 is activated during the ER stress response, which results in acute ADP-ribosylation of GRP78/BiP paralleling translational inhibition. Thus, this identification of ARTC1 as a regulator of GRP78/BiP defines a novel, previously unsuspected, player in GRP78-mediated ER stress responses.

Intracellular Ca(2+) release from endoplasmic reticulum regulates slow wave currents and pacemaker activity of interstitial cells of Cajal

Interstitial cells of Cajal (ICC) provide pacemaker activity in gastrointestinal muscles that underlies segmental and peristaltic contractions. ICC generate electrical slow waves that are due to large-amplitude inward currents resulting from anoctamin 1 (ANO1) channels, which are Ca(2+)-activated Cl(-) channels. We investigated the hypothesis that the Ca(2+) responsible for the stochastic activation of ANO1 channels during spontaneous transient inward currents (STICs) and synchronized activation of ANO1 channels during slow wave currents comes from intracellular Ca(2+) stores. ICC, obtained from the small intestine of Kit(+/copGFP) mice, were studied under voltage and current clamp to determine the effects of blocking Ca(2+) uptake into stores and release of Ca(2+) via inositol 1,4,5-trisphosphate (IP3)-dependent and ryanodine-sensitive channels. Cyclocpiazonic acid, thapsigargin, 2-APB, and xestospongin C inhibited STICs and slow wave currents. Ryanodine and tetracaine also inhibited STICs and slow wave currents. Store-active compounds had no direct effects on ANO1 channels expressed in human embryonic kidney-293 cells. Under current clamp, store-active drugs caused significant depolarization of ICC and reduced spontaneous transient depolarizations (STDs). After block of ryanodine receptors with ryanodine and tetracaine, repolarization did not restore STDs. ANO1 expressed in ICC has limited access to cytoplasmic Ca(2+) concentration, suggesting that pacemaker activity depends on Ca(2+) dynamics in restricted microdomains. Our data from studies of isolated ICC differ somewhat from studies on intact muscles and suggest that release of Ca(2+) from both IP3 and ryanodine receptors is important in generating pacemaker activity in ICC.

Migration and Phagocytic Ability of Activated Microglia During Post-natal Development is Mediated by Calcium-Dependent Purinergic Signalling

Microglia play an important role in synaptic pruning and controlled phagocytosis of neuronal cells during developmental stages. However, the mechanisms that regulate these functions are not completely understood. The present study was designed to investigate the role of purinergic signalling in microglial migration and phagocytic activity during post-natal brain development. One-day-old BALB/c mice received lipopolysaccharide (LPS) and/or a purinergic analogue (2-methylthioladenosine-5'-diphosphate; 2MeSADP), intracerebroventrically (i.c.v.). Combined administration of LPS and 2MeSADP resulted in activation of microglia as evident from increased expression of ionised calcium-binding adapter molecule 1 (Iba1). Activated microglia showed increased expression of purinergic receptors (P2Y2, P2Y6 and P2Y12). LPS either alone or in combination with 2MeSADP induced the expression of Na(+)/Ca(2+) exchanger (NCX-1) and P/Q-type Ca(2+) channels along with MARCKS-related protein (MRP), which is an integral component of cell migration machinery. In addition, LPS and 2MeSADP administration induced the expression of microglial CD11b and DAP12 (DNAX-activation protein 12), which are known to be involved in phagocytosis of neurons during development. Interestingly, administration of thapsigargin (TG), a specific Ca(2+)-ATPase inhibitor of endoplasmic reticulum, prevented the LPS/2MeSADP-induced microglial activation and migration by down-regulating the expression of Iba1 and MRP, respectively. Moreover, TG also reduced the LPS/2MeSADP-induced expression of CD11b/DAP12. Taken together, the findings reveal for the first time that Ca(2+)-mediated purinergic receptors regulate the migration and phagocytic ability of microglia during post-natal brain development.

Reduced IRE1α mediates apoptotic cell death by disrupting calcium homeostasis via the InsP3 receptor

The endoplasmic reticulum (ER) is not only a home for folding and posttranslational modifications of secretory proteins but also a reservoir for intracellular Ca(2+). Perturbation of ER homeostasis contributes to the pathogenesis of various neurodegenerative diseases, such as Alzheimer's and Parkinson diseases. One key regulator that underlies cell survival and Ca(2+) homeostasis during ER stress responses is inositol-requiring enzyme 1α (IRE1α). Despite extensive studies on this ER membrane-associated protein, little is known about the molecular mechanisms by which excessive ER stress triggers cell death and Ca(2+) dysregulation via the IRE1α-dependent signaling pathway. In this study, we show that inactivation of IRE1α by RNA interference increases cytosolic Ca(2+) concentration in SH-SY5Y cells, leading to cell death. This dysregulation is caused by an accelerated ER-to-cytosolic efflux of Ca(2+) through the InsP3 receptor (InsP3R). The Ca(2+) efflux in IRE1α-deficient cells correlates with dissociation of the Ca(2+)-binding InsP3R inhibitor CIB1 and increased complex formation of CIB1 with the pro-apoptotic kinase ASK1, which otherwise remains inactivated in the IRE1α-TRAF2-ASK1 complex. The increased cytosolic concentration of Ca(2+) induces mitochondrial production of reactive oxygen species (ROS), in particular superoxide, resulting in severe mitochondrial abnormalities, such as fragmentation and depolarization of membrane potential. These Ca(2+) dysregulation-induced mitochondrial abnormalities and cell death in IRE1α-deficient cells can be blocked by depleting ROS or inhibiting Ca(2+) influx into the mitochondria. These results demonstrate the importance of IRE1α in Ca(2+) homeostasis and cell survival during ER stress and reveal a previously unknown Ca(2+)-mediated cell death signaling between the IRE1α-InsP3R pathway in the ER and the redox-dependent apoptotic pathway in the mitochondrion.

Calcium signaling in lacrimal glands

Lacrimal glands provide the important function of lubricating and protecting the ocular surface. Failure of proper lacrimal gland function results in a number of debilitating dry eye diseases. Lacrimal glands secrete lipids, mucins, proteins, salts and water and these secretions are at least partially regulated by neurotransmitter-mediated cell signaling. The predominant signaling mechanism for lacrimal secretion involves activation of phospholipase C, generation of the Ca(2+)-mobilizing messenger, IP3, and release of Ca(2+) stored in the endoplasmic reticulum. The loss of Ca(2+) from the endoplasmic reticulum then triggers a process known as store-operated Ca(2+) entry, involving a Ca(2+) sensor in the endoplasmic reticulum, STIM1, which activates plasma membrane store-operated channels comprised of Orai subunits. Recent studies with deletions of the channel subunit, Orai1, confirm the important role of SOCE in both fluid and protein secretion in lacrimal glands, both in vivo and in vitro.

The antibody-drug conjugate: an enabling modality for natural product-based cancer therapeutics

The Antibody Drug Conjugate (ADC) is a therapeutic modality consisting of a monoclonal antibody attached to a cytotoxic, small-molecule payload. The antibody portion of the ADC serves as a transport vehicle that recognizes and binds to a protein antigen expressed in tumor tissues. The localized delivery and release of the payload within or near malignant cells allows for targeted delivery of a potent cytotoxic agent to diseased tissue, while reducing damage to antigen-negative, normal tissues. Recent years have witnessed an explosive increase in ADC-based therapies, due mainly to clinical reports of activity in both hematologic and epithelial cancers. Accompanying this upsurge in ADC development is a renewed interest in natural product cytotoxins, which are typically highly potent cell-killing agents, but suffer from poor drug-like properties and narrow safety margins when systemically administered as conventional chemotherapeutics. In this review, we discuss recent advances related to the construction of ADCs, the optimization of ADC safety and efficacy, and the increasingly pivotal roles of natural product payloads in the current and future landscape of ADC therapy.

Calcineurin-mediated dephosphorylation of eNOS at serine 116 affects eNOS enzymatic activity indirectly by facilitating c-Src binding and tyrosine 83 phosphorylation

It has been shown previously that phosphorylation of the endothelial nitric oxide synthase (eNOS) at serine 116 (S116) under basal conditions suppresses eNOS enzymatic activity in endothelial cells. It has also been shown that vascular endothelial growth factor (VEGF) treatment of endothelial cells produces a rapid S116 dephosphorylation, which is blocked by the calcineurin inhibitor, cyclosporin A (CsA). In this study, we show that activation of eNOS in response to a variety of other eNOS-activating agonists and the cytosolic calcium-elevating agent, thapsigargin also involves CsA-inhibitable S116 dephosphorylation. Studies with the purified eNOS enzyme also demonstrate that neither mimicking phosphorylation at S116 nor phosphorylation of the purified enzyme at S116 in vitro has any effect on enzymatic activity. Phospho-mimicking, however, does interfere with the interaction of eNOS with c-Src, an interaction which is known to activate eNOS by phosphorylation at tyrosine 83 (Y83). Agonist-stimulated eNOS-Src complex formation, as well as agonist-stimulated Y83 phosphorylation, are blocked by calcineurin inhibition by CsA and by a cell-permeable calcineurin inhibitory peptide. Taken together, these data suggest a mechanism of eNOS regulation whereby calcineurin-mediated dephosphorylation of eNOS at S116 affects eNOS enzymatic activity indirectly, rather than directly, by facilitating c-Src binding and Y83 phosphorylation.

Airway smooth muscle CXCR3 ligand production: regulation by JAK-STAT1 and intracellular Ca²⁺

In asthma, airway smooth muscle (ASM) chemokine (C-X-C motif) receptor 3 (CXCR3) ligand production may attract mast cells or T lymphocytes to the ASM, where they can modulate ASM functions. In ASM cells (ASMCs) from people with or without asthma, we aimed to investigate JAK-STAT1, JNK, and Ca²⁺ involvement in chemokine (C-X-C motif) ligand (CXCL)10 and CXCL11 production stimulated by interferon-γ, IL-1β, and TNF-α combined (cytomix). Confluent, growth-arrested ASMC were treated with inhibitors for pan-JAK (pyridone-6), JAK2 (AG-490), JNK (SP-600125), or the sarco(endo)plasmic reticulum Ca²⁺ATPase (SERCA) pump (thapsigargin), Ca²⁺ chelator (BAPTA-AM), or vehicle before and during cytomix stimulation for up to 24 h. Signaling protein activation as well as CXCL10/CXCL11 mRNA and protein production were examined using immunoblot analysis, real-time PCR, and ELISA, respectively. Cytomix-induced STAT1 activation was lower and CXCR3 ligand mRNA production was more sensitive to pyridone-6 and AG-490 in asthmatic than nonasthmatic ASMCs, but CXCL10/CXCL11 release was inhibited by the same proportion. Neither agent caused additional inhibition of release when used in combination with the JNK inhibitor SP-600125. Conversely, p65 NF-κB activation was higher in asthmatic than nonasthmatic ASMCs. BAPTA-AM abolished early CXCL10/CXCL11 mRNA production, whereas thapsigargin reduced it in asthmatic cells and inhibited CXCL10/CXCL11 release by both ASMC types. Despite these inhibitory effects, neither Ca²⁺ agent affected early activation of STAT1, JNK, or p65 NF-κB. In conclusion, intracellular Ca²⁺ regulated CXCL10/CXCL11 production but not early activation of the signaling molecules involved. In asthma, reduced ASM STAT1-JNK activation, increased NF-κB activation, and altered Ca²⁺ handling may contribute to rapid CXCR3 ligand production and enhanced inflammatory cell recruitment.

Linkages between the life-history evolution of tropical and temperate birds and the resistance of cultured skin fibroblasts to oxidative and non-oxidative chemical injury

A fundamental challenge facing physiological ecologists is to understand how variation in life history at the whole-organism level might be linked to cellular function. Thus, because tropical birds have higher annual survival and lower rates of metabolism, we hypothesized that cells from tropical species would have greater cellular resistance to chemical injury than cells from temperate species. We cultured dermal fibroblasts from 26 tropical and 26 temperate species of birds and examined cellular resistance to cadmium, H(2)O(2), paraquat, thapsigargin, tunicamycium, methane methylsulfonate (MMS) and UV light. Using ANCOVA, we found that the values for the dose that killed 50% of cells (LD(50)) from tropical birds were significantly higher for H(2)O(2) and MMS. When we tested for significance using a generalized least squares approach accounting for phylogenetic relationships among species to model LD(50), we found that cells from tropical birds had greater tolerance for Cd, H(2)O(2), paraquat, tunicamycin and MMS than cells from temperate birds. In contrast, tropical birds showed either lower or no difference in tolerance to thapsigargin and UV light in comparison with temperate birds. These findings are consistent with the idea that natural selection has uniquely fashioned cells of long-lived tropical bird species to be more resistant to forms of oxidative and non-oxidative stress than cells from shorter-lived temperate species.

Activation of calcium-insensitive phospholipase A(2) (iPLA(2)) by P2X(7) receptors in murine peritoneal macrophages

Free fatty acid releases are triggered by PLA2 activation and are substrates for many enzymes such as cyclooxygenases. These reactions are responsible for the production of many prostaglandins implicated in the inflammation yet many purinergic receptors have been implicated in diseases characterised by chronic inflammation. The role of P2X receptors was evaluated in LPS-primed murine peritoneal macrophages which were labelled with either [(3)H]-oleic acid or [(3)H]-arachidonic acid. Ten μmolar thapsigargin and 1mM ATP stimulated the release of both unsaturated acids. ATP had no effect at 10 μM and ivermectin had no effect on the response to ATP. The response to ATP was inhibited by magnesium and was not observed with cells from P2X(7)(-/-) mice. The response to ATP was not affected by the removal of extracellular calcium and was inhibited by arachidonyltrifluoromethyl ketone and bromoenol lactone but not by pyrrophenone. The release of the [(3)H]-fatty acids by ATP and thapsigargin was diminished by PD-98058, an inhibitor of MEK-1. It was concluded that in LPS-primed macrophages, P2X(7) receptors, not P2X(4) receptors, activated an iPLA(2) and promoted the release of unsaturated fatty acids secondary to the activation of a kinase. This response might contribute to the inflammation provoked by extracellular ATP.

Deficient mitochondrial Ca(2+) buffering in the Cln8(mnd) mouse model of neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) are a group of genetic childhood-onset progressive brain diseases characterized by a decline in mental and motor capacities, epilepsy, visual loss and premature death. Using patch clamp, fluorescence imaging and caged Ca(2+) photolysis, we evaluated the mechanisms of neuronal Ca(2+) clearance in Cln8(mnd) mice, a model of the human NCL caused by mutations in the CLN8 gene. In Cln8(mnd) hippocampal slices, Ca(2+) clearance efficiency in interneurons and, to some extent, principal neurons declined with age. In cultured Cln8(mnd) hippocampal neurons, clearance of large Ca(2+) loads was inefficient due to impaired mitochondrial Ca(2+) uptake. In contrast, neither Ca(2+) uptake by sarco/endoplasmic reticulum Ca(2+) ATPase, nor Ca(2+) extrusion through plasma membrane was affected by the Cln8 mutation. Excitotoxic glutamate challenge caused Ca(2+) deregulation more readily in Cln8(mnd) than in wt neurons. We propose that neurodegeneration in human CLN8 disorders is primarily caused by reduced mitochondrial Ca(2+) buffering capacity.

Nucleotides control the excitability of sensory neurons via two P2Y receptors and a bifurcated signaling cascade

Nucleotides contribute to the sensation of acute and chronic pain, but it remained enigmatic which G protein-coupled nucleotide (P2Y) receptors and associated signaling cascades are involved. To resolve this issue, nucleotides were applied to dorsal root ganglion neurons under current- and voltage-clamp. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), and uridine triphosphate (UTP), but not uridine diphosphate (UDP), depolarized the neurons and enhanced action potential firing in response to current injections. The P2Y₂ receptor preferring agonist 2-thio-UTP was equipotent to UTP in eliciting these effects. The selective P2Y₁ receptor antagonist MRS2179 largely attenuated the excitatory effects of ADP, but left those of 2-thio-UTP unaltered. Thus, the excitatory effects of the nucleotides were mediated by 2 different P2Y receptors, P2Y₁ and P2Y₂. Activation of each of these 2 receptors by either ADP or 2-thio-UTP inhibited currents through K_V7 channels, on one hand, and facilitated currents through TRPV₁ channels, on the other hand. Both effects were abolished by inhibitors of phospholipase C or Ca²⁺-ATPase and by chelation of intracellular Ca²⁺. The facilitation of TRPV₁, but not the inhibition K_V7 channels, was prevented by a protein kinase C inhibitor. Simultaneous blockage of K_V7 channels and of TRPV₁ channels prevented nucleotide-induced membrane depolarization and action potential firing. Thus, P2Y₁ and P2Y₂ receptors mediate an excitation of dorsal root ganglion neurons by nucleotides through the inhibition of K_V7 channels and the facilitation of TRPV₁ channels via a common bifurcated signaling pathway relying on an increase in intracellular Ca²⁺ and an activation of protein kinase C, respectively.

Gene targeting and Calcium handling efficiencies in mouse embryonic stem cell lines

AIM

To compare gene targeting efficiencies, expression profiles, and Ca(2+) handling potentials in two widely used mouse embryonic stem cell lines.

METHODS

The two widely used mouse embryonic stem cell lines, R1 and HM-1, were cultured and maintained on Mitomycin C treated mouse embryonic fibroblast feeder cell layers, following standard culture procedures. Cells were incubated with primary and secondary antibodies before fluorescence activated cell sorting analysis to compare known pluripotency markers. Moreover, cells were harvested by trypsinization and transfected with a kinase-inactive murine Tyk2 targeting construct, following the BioRad and Amaxa transfection procedures. Subsequently, the cells were cultured and neomycin-resistant cells were picked after 13 d of selection. Surviving clones were screened twice by polymerase chain reaction (PCR) and finally confirmed by Southern blot analysis before comparison. Global gene expression profiles of more than 20 400 probes were also compared and significantly regulated genes were confirmed by real time PCR analysis. Calcium handling potentials of these cell lines were also compared using various agonists.

RESULTS

We found significant differences in transfection efficiencies of the two cell lines (91% ± 6.1% vs 75% ± 4.2%, P = 0.01). Differences in the targeting efficiencies were also significant whether the Amaxa or BioRad platforms were used for comparison. We did not observe significant differences in the levels of many known pluripotency markers. However, our genome-wide expression analysis using more than 20 400 spotted cDNA arrays identified 55 differentially regulated transcripts (P < 0.05) implicated in various important biological processes, including binding molecular functions (particularly Ca(2+) binding roles). Subsequently, we measured Ca(2+) signals in these cell lines in response to various calcium agonists, both in high and low Ca(2+) solutions, and found significant differences (P < 0.05) in the regulation of Ca(2+) homeostasis between the investigated cell lines. Then we further compared the detection and expression of various membrane and intracellular Ca(2+) receptors and similarly found significant (P < 0.05) variations in a number of calcium receptors between these cell lines.

CONCLUSION

Results of this study emphasize the importance of considering intrinsic cellular variations, during selection of cell lines for experiments and interpretations of experimental results.

Initial calcium release from intracellular stores followed by calcium dysregulation is linked to secondary axotomy following transient axonal stretch injury

Acute axonal shear and stretch in the brain induces an evolving form of axonopathy and is a major cause of ongoing motor, cognitive and emotional dysfunction. We have utilized an in vitro model of mild axon bundle stretch injury, in cultured primary cortical neurons, to determine potential early critical cellular alterations leading to secondary axonal degeneration. We determined that transient axonal stretch injury induced an initial acute increase in intracellular calcium, principally derived from intracellular stores, which was followed by a delayed increase in calcium over 48 h post-injury (PI). This progressive and persistent increase in intracellular calcium was also associated with increased frequency of spontaneous calcium fluxes as well as cytoskeletal abnormalities. Additionally, at 48 h post-injury, stretch-injured axon bundles demonstrated filopodia-like sprout formation that preceded secondary axotomy and degeneration. Pharmacological inhibition of the calcium-activated phosphatase, calcineurin, resulted in reduced secondary axotomy (p < 0.05) and increased filopodial sprout length. In summary, these results demonstrate that stretch injury of axons induced an initial substantial release of calcium from intracellular stores with elevated intracellular calcium persisting over 2 days. These long-lasting calcium alterations may provide new insight into the earliest neuronal abnormalities that follow traumatic brain injury as well as the key cellular changes that lead to the development of diffuse axonal injury and secondary degeneration.

Nematicidal activity of two monoterpenoids and SER-2 tyramine receptor of Caenorhabditis elegans

In vitro cultures of two nematodes (Caenorhabditis elegans and Ascaris suum) were established to study the nematicidal activity of three monoterpenoids (thymol, carvacrol and p-cymene). Toxicity of thymol and carvacrol was found for the two nematodes tested. The study was then aimed to address whether nematode tyramine receptor (TyrR) could interact with the two compounds by using HEK293 mammalian cells transfected with a C. elegans TyrR (ser-2) sequence, in hope of developing a high-throughput cell-based platform for future screening of new antihelminthic compounds. SER-2 expression and functionality in the transfected cells was first confirmed by green fluorescent protein tagging, competitive receptor binding, intracellular cyclic AMP, and intracellular calcium [Ca(2+)](i) mobilization assays. Thymol and carvacrol were then tested and demonstrated to interact with TyrR in desensitizing SER-2 for tyramine activation in [Ca(2+)](i) mobilization assay, and in translocating SER-2 from membrane to cytoplasm in receptor internalization assay. Receptor internalization activity of thymol and carvacrol was significantly blocked in cells expressing mutant SER-2 with the S210A/S214A double mutations, thus confirming specificity of the interactions. In summary, the current study showed that the nematicidal activity of thymol and carvacrol might be mediated through TyrR as the two compounds could trigger the signaling cascade downstream from the receptor in cells expressing wild-type but not a mutant SER-2. The TyrR-expressing cell system may prove to be a good screening platform for developing new antihelmintic compounds that may overcome parasite drug resistance, especially when such chemicals are used in combination with commercial drugs.

Unlike the synchronous Plasmodium falciparum and P. chabaudi infection, the P. berghei and P. yoelii asynchronous infections are not affected by melatonin

We have previously reported that Plasmodium chabaudi and P. falciparum sense the hormone melatonin and this could be responsible for the synchrony of malaria infection. In P. chabaudi and P. falciparum, melatonin induces calcium release from internal stores, and this response is abolished by U73122, a phospholipase C inhibitor, and luzindole, a melatonin-receptor competitive antagonist. Here we show that, in vitro, melatonin is not able to modulate cell cycle, nor to elicit an elevation in intracellular calcium concentration of the intraerythrocytic forms of P. berghei or P. yoelii, two rodent parasites that show an asynchrononous development in vivo. Interestingly, melatonin and its receptor do not seem to play a role during hepatic infection by P. berghei sporozoites either. These data strengthen the hypothesis that host-derived melatonin does not synchronize malaria infection caused by P. berghei and P. yoelii. Moreover, these data explain why infections by these parasites are asynchronous, contrary to what is observed in P. falciparum and P. chabaudi infections.

Gamma-radiation induces apoptosis via sarcoplasmatic reticulum in guinea pig ileum smooth muscle cells

We investigated the effects of gamma-radiation on cells isolated from the longitudinal smooth muscle layer of the guinea pig ileum, a relatively radioresistant tissue. Single doses (up to 50 Gy) reduced the amount of sarcoplasmatic reticulum and condensed the myofibrils, as shown by electron microscopy 3 days post-irradiation. After that, contractility of smooth muscle strips was reduced. Ca(2+) handling was altered after irradiation, as shown in fura-2 loaded cells, with elevated basal intracellular Ca(2+), reduced amount of intrareticular Ca(2+), and reduced capacitive Ca(2+) entry. Radiation also induced apoptosis, judged from flow cytometry of cells loaded with proprium iodide. Electron microscopy showed that radiation caused condensation of chromatin in dense masses around the nuclear envelope, the presence of apoptotic bodies, fragmentation of the nucleus, detachment of cells from their neighbors, and reductions in cell volume. Radiation also caused activation of caspase 12. Apoptosis was reduced by the administration of the caspase inhibitor Z-Val-Ala-Asp-fluoromethyl-ketone methyl ester (Z-VAD-FMK) during the 3 day period after irradiation, and by the chelator of intracellular Ca(2+), 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), from 1 h before until 2 h after irradiation. BAPTA also reduced the effects of radiation on contractility, basal intracellular Ca(2+), amount of intrareticular Ca(2+), capacitative Ca(2+) entry, and apoptosis. In conclusion, the effects of gamma radiation on contractility, Ca(2+) handling, and apoptosis appear due to a toxic action of intracellular Ca(2+). Ca(2+)-induced damage to the sarcoplasmatic reticulum seems a key event in impaired Ca(2+) handling and apoptosis induced by gamma-radiation.

Maintaining low Ca2+ level in the endoplasmic reticulum restores abnormal endogenous F508del-CFTR trafficking in airway epithelial cells

The most common mutation in cystic fibrosis, F508del, results in cystic fibrosis transmembrane conductance regulator protein (CFTR) that is retained in the endoplasmic reticulum (ER). Retention is dependent on chaperone proteins, many of which, like calnexin, require calcium for optimal activity. Here, we show that a limited and a maintained ER calcium level is sufficient to inhibit the F508del-CFTR/calnexin interaction and to restore the cAMP-dependent CFTR chloride transport, thus showing the correction of abnormal trafficking. We used Western blot analysis, iodide efflux and calcium measurement techniques applied to the human airway epithelial cystic fibrosis cell line CF15 (F508del/F508del). The inhibition of ER calcium pump, with thapsigargin, curcumin, 2,5-di(t-butyl)hydroquinone or cyclopiazonic acid, maintains a threshold levels of calcium that is correlated to the recovery of endogenous F508del-CFTR transport activity. In particular, cyclopiazonic acid restores a 2-aminoethyoxydiphenyl borate-sensitive F508del-CFTR trafficking with an EC50 of 915 nm. By contrast, the 1,4,5-trisphosphate or IP3 receptor activators, i.e., ATP and histamine, while transiently emptying the ER intracellular calcium store, did not affect the trafficking of F508del-CFTR. Our data suggest that decreasing the ER calcium level is not sufficient to restore the defective trafficking of F508del-CFTR, whereas decreasing and also maintaining low ER calcium level allow correction of defective biosynthetic pathway of endogenous F508del-CFTR in human airway epithelial cells.

Novel neuroprotective compound SCH-20148 rescues thymocytes and SH-SY5Y cells from thapsigargin-induced mitochondrial membrane potential reduction and cell death

Mitochondrial membrane potential plays an important role in cell survival. Transitions in mitochondrial permeability, which indicate the imminent destruction of the organelles, have been observed in damaged neuronal cells both in vitro and in vivo. In this study, C57/BL6n mouse thymocytes were put under stress using thapsigargin, a Ca2+ ATP-ase inhibitor, after which the change in mitochondrial membrane potential was monitored with a JC-1 dual-emission probe. This was done in an attempt to identify a novel compound that can suppress mitochondrial membrane potential reduction and cell death. In this assay system, the novel compound SCH-20148 [2,3-dihydroxypropyl-5-bromo-N-(2-methyl-3-trifluoromethylphenyl)anthranilate] was found to protect mouse thymocytes against thapsigargin (3 nM)-induced mitochondrial membrane potential reduction (IC50=42 nM). SCH-20148 also prevented A23187- or ionomycin-induced shifts in mitochondrial membrane potential but it did not have any effect on the changes induced by tunicamycin, staurosporine, or dexamethasone. The potent immunosuppressants tacrolimus and cyclosporine A prevented the effect of thapsigargin, but did not prevent the A23187- or ionomycin-induced changes. Calcium-modulating agents, an anti-oxidant, a protein kinase C inhibitor, and anti-inflammatory agents were not effective against thapsigargin-induced mitochondrial permeability transition which implies that SCH-20148 exerts a protective effect via its specific mechanism. In addition, SH-20148 demonstrated a neuroprotective effect against thapsigargin-induced neuronal cell death in neuroblastoma SH-SY5Y cells. Taken together, these results suggest the potential of SCH-20148 as novel neuroprotective drug.

Calcium movements during pigment aggregation in freshwater shrimp chromatophores

Pigment granule migration within crustacean chromatophores provides an excellent model with which to investigate cytoplasmic movements, given the antagonistic, neurosecretory peptide regulation of granule translocation, and the absence of innervation in these large, brightly colored cells. Red pigment-concentrating hormone (RPCH) induces pigment aggregation in shrimp chromatophores via an increase in intracellular Ca2+; however, how this increase is brought about is not known. To examine the putative Ca2+ movements leading to pigment translocation in red, ovarian chromatophores of the freshwater shrimp, Macrobrachium olfersii, this study manipulates intra- and extracellular Ca2+ employing ER Ca2+-ATPase inhibitors, ryanodine-sensitive, ER Ca2+ channel blockers, and EDTA/EGTA-buffered A23187/Ca2+-containing salines. Our findings reveal that during pigment aggregation, cytosolic Ca2+ apparently increases from an intracellular source, the abundant SER, loaded by the SERCA and released through ryanodine-sensitive receptor/channels, triggered by capacitative calcium influx and/or calcium-induced calcium release mechanisms. Aggregation also depends on external calcium, which may modulate RPCH/receptor coupling. Such calcium-regulated pigment movements form the basis of a complex system of chromatic adaptation, which confers selective advantages like camouflage and protection against ultra-violet radiation to this palaemonid shrimp.

Discovering the mechanism of capacitative calcium entry

This essay examines the historical significance of an APS classic paper that is freely available online:

Kwan CY, Takemura H, Obie JF, Thastrup O, and Putney JW Jr.

Effects of MeCh, thapsigargin, and La3+on plasmalemmal and intracellular Ca2+transport in lacrimal acinar cells. Am J Physiol Cell Physiol 258: C1006–C1015, 1990. ( http://ajpcell.physiology.org/cgi/reprint/258/6/C1006 )

Lead inhibited N-methyl-D-aspartate receptor-independent long-term potentiation involved ryanodine-sensitive calcium stores in rat hippocampal area CA1

Lead exposure is known to be associated with cognitive dysfunction in children. Impairment of the induction of long-term potentiation (LTP) has been reported in area CA1 of rat hippocampus following lead exposure in vivo and in vitro. The present study was carried out to investigate whether the alterations of N-methyl-d-aspartate (NMDA) receptor-independent LTP following lead exposure involve internal calcium stores in hippocampus CA1 synapses. Monosynaptic field excitatory postsynaptic potentials in hippocampal slice area CA1 were recorded using the whole-cell patch-clamp upon acute lead treatment, and these studies were coupled with calcium imaging experiments to observe internal calcium changes in cultured hippocampal neurons. Inhibiting calcium release by ryanodine significantly reduced NMDA receptor-independent LTP, and depletion of internal calcium stores with thapsigargin blocked this form of LTP. Caffeine, an agonist of ryanodine receptors, enhanced this form of LTP. However, caffeine-enhanced NMDA receptor-independent LTP was depressed after bath application of lead. Moreover, lead further decreased ryanodine- and thapsigargin-reduced NMDA receptor-independent LTP. Calcium imaging also confirmed that lead had an effect on internal calcium release and uptake. Taken together, these results demonstrated that lead inhibited NMDA receptor-independent LTP by action on calcium release and uptake by ryanodine-sensitive stores in rat hippocampal area CA1.

Changes in guinea pig gallbladder smooth muscle Ca2+ homeostasis by acute acalculous cholecystitis

Impaired smooth muscle contractility is a hallmark of acute acalculous cholecystitis. Although free cytosolic Ca2+ ([Ca2+]i) is a critical step in smooth muscle contraction, possible alterations in Ca2+ homeostasis by cholecystitis have not been elucidated. Our aim was to elucidate changes in the Ca2+ signaling pathways induced by this gallbladder dysfunction. [Ca2+]i was determined by epifluorescence microscopy in fura 2-loaded isolated gallbladder smooth muscle cells, and isometric tension was recorded from gallbladder muscle strips. F-actin content was quantified by confocal microscopy. Ca2+ responses to the inositol trisphosphate (InsP3) mobilizing agonist CCK and to caffeine, an activator of the ryanodine receptors, were impaired in cholecystitic cells. This impairment was not the result of a decrease in the size of the releasable pool. Inflammation also inhibited Ca2+ influx through L-type Ca2+ channels and capacitative Ca2+ entry induced by depletion of intracellular Ca2+ pools. In addition, the pharmacological phenotype of these channels was altered in cholecystitic cells. Inflammation impaired contractility further than Ca2+ signal attenuation, which could be related to the decrease in F-actin that was detected in cholecystitic smooth muscle cells. These findings indicate that cholecystitis decreases both Ca2+ release and Ca2+ influx in gallbladder smooth muscle, but a loss in the sensitivity of the contractile machinery to Ca2+ may also be responsible for the impairment in gallbladder contractility.

Endothelin-1 increases intracellular Ca(2+) in rabbit pulmonary artery smooth muscle cells through phospholipase C

In freshly isolated rabbit pulmonary artery smooth muscle cells, endothelin (ET)-1 induced a transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) followed by a return to the initial [Ca(2+)](i). This response was not abolished by the voltage-dependent Ca(2+) channel blocker nicardipine or removal of Ca(2+) from the bath solution but was inhibited by ryanodine and thapsigargin. This finding suggested that the increase in [Ca(2+)](i) induced by ET-1 was attributable to release of Ca(2+) from ryanodine- and inositol 1,4,5-trisphosphate-sensitive intracellular Ca(2+) stores. The transient increase in [Ca(2+)](i) induced by ET-1 was also inhibited by pretreatment with antagonists of ET type A and B (ET(A) and ET(B)) receptors (BQ-123 and BQ-788, respectively). Furthermore, the ET(B) receptor agonist IRL-1620 induced an increase in [Ca(2+)](i) that was followed by a sustained increase in [Ca(2+)](i); the sustained increase in [Ca(2+)](i) was blocked by nicardipine. Using the nystatin-perforated patch-clamp technique, we found that IRL-1620 caused an increase in Ca(2+) current that was inhibited by addition of ET-1. ET-1 did not inhibit Ca(2+) current when cells were pretreated with BQ-123. These results suggested that when both receptor types are activated, the opposing responses lead to abolition of the sustained [Ca(2+)](i) increases induced by ET(B) receptor activation. Western blot analysis confirmed expression of ET(A) and ET(B) receptors. Finally, U-73122 inhibited the ET-1-induced [Ca(2+)](i) increase, indicating that phospholipase C was involved in modulation of the ET-1-induced [Ca(2+)](i) increase in rabbit pulmonary artery smooth muscle cells.

Involvement of protein kinase C in the inhibition of lipopolysaccharide-induced nitric oxide production by thapsigargin in RAW 264.7 macrophages

This study explored the effects of inhibition of endoplasmic reticulum (ER) Ca(2+)-ATPase on lipopolysaccharide (LPS)-induced protein kinase C (PKC) activation, nuclear factor-kappaB (NF-kappaB) translocation, inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in RAW 264.7 macrophages. Thapsigargin (TG) irreversibly inhibits ER Ca(2+)-ATPase and LPS-induced NO production is reduced even after washout. TG also attenuated LPS-stimulated iNOS expression by using immunoblot analysis. However, another distinct fully reversible ER Ca(2+)-ATPase inhibitor, 2,5-di-tert-butylhydroquinone (DBHQ), ionophore A23187 and ionomycin could exert a similar effect to TG in increasing intracellular calcium concentration; however, these agents could not mimic TG in reducing iNOS expression and NO production. LPS increased PKC-alpha and -beta activation, and TG pretreatment attenuated LPS-stimulated PKC activation. Not did pretreatment with DBHQ, A23187 and ionomycin reduce LPS-stimulated PKC activation. Furthermore, NF-kappaB-specific DNA-protein-binding activity in the nuclear extracts was enhanced by treatment with LPS, and TG pretreatment attenuated LPS-stimulated NF-kappaB activation. None of DBHQ, A23187 and ionomycin pretreatment reduced LPS-stimulated NF-kappaB activation. These data suggest that persistent inhibition of ER Ca(2+)-ATPase by TG would influence calcium release from ER Ca2+ pools that was stimulated by the LPS activated signal processes, and might be the main mechanism for attenuating PKC and NF-kappaB activation that induces iNOS expression and NO production.

Intracellular calcium and protein tyrosine phosphorylation during the release of bovine sperm adhering to the fallopian tube epithelium in vitro

In mammals, sperm adhesion to the epithelial cells lining the oviductal isthmus plays a key role in the maintenance of motility and in the selection of superior quality subpopulations. In the bovine species, heparin and other sulfated glycoconjugates powerfully induce the synchronous release of sperm adhering to tubal epitheliumin vitroand may represent the signal which triggers release at ovulationin vivo. Sperm detachment may be due either to surface remodeling or to hyperactivation brought about by capacitation. In this paper, the dynamics of intracellular free Ca2+concentration ([Ca2+]i) and protein tyrosine phosphorylation in sperm during and after heparin-induced release fromin vitrocultured oviductal monolayers were assessed to determine whether this event is due to capacitation. Moreover, Ca2+-ionophore A23187, thapsigargin, thimerosal and caffeine were used to determine whether [Ca2+]iincrease and/or hyperactivation can induce sperm release. Results showed that: 1. heparin-released sperm have significantly higher [Ca2+]ithan adhering sperm; 2. heparin induces a [Ca2+]ielevation in the sperm head followed by detachment from the monolayers; 3. external Ca2+is not required for heparin-induced release; 4. [Ca2+]iincrease and/or hyperactivation are unable to release sperm; and 5. heparin-released sperm have an increased level of tyrosine phosphorylated proteins compared with adhering sperm. In conclusion, although heparin is considered a long-lasting capacitation agent, it quickly modulates the capacitation of bovine sperm adhering to the fallopian epithelium, probably leading to surface remodeling and therefore to the release of sperm selected and stored within the oviduct through adhesion.

Effects of intracellular stores and extracellular Ca(2+) on Ca(2+)-activated K(+) currents in mature mouse inner hair cells

Ca(2+)-activated K(+) currents were studied in inner hair cells (IHCs) of mature mice. I(K,f), the large-conductance Ca(2+)-activated K(+) current (BK) characteristic of mature IHCs, had a fast activation time constant (0.4 ms at -25 mV at room temperature) and did not inactivate during 170 ms. Its amplitude, measured at -25 mV, and activation time constant were similar between IHCs in the apical and basal regions of the cochlea. I(K,f) was selectively blocked by 30 nm IbTx but was unaffected by superfusion of Ca(2+)-free solution, nifedipine or Bay K 8644, excluding the direct involvement of voltage-gated Ca(2+) channels in I(K,f) activation. Increasing the intracellular concentration of the Ca(2+) chelator BAPTA from 0.1 mm to 30 mm reduced the amplitude of I(K,f) at -25 mV and shifted its activation by 37 mV towards more depolarized potentials. A reduction in the size of I(K,f) and a depolarizing shift of its activation were also seen when either thapsigargin and caffeine or ryanodine were added intracellularly, suggesting that I(K,f) is modulated by voltage-dependent release from intracellular Ca(2+) stores. Mature IHCs had a small additional Ca(2+)-activated K(+) current (I(K(Ca))), activated by Ca(2+) flowing through L-type Ca(2+) channels. This current was still present during superfusion of either IbTx (60 nm) or apamin (300 nm) but was abolished in Cs(+)-based intracellular solution or during superfusion of 5 mm TEA, suggesting the presence of an additional BK-channel type. Current clamp experiments at body temperature show that I(K,f), but not I(K(Ca)), is essential for fast voltage responses of mature IHCs.

Germacranolides from seeds of the endangered Umbelliferae species Rouya polygama

From the etheral extract of Rouya polygama Coincy seeds (Umbelliferae) six new germacranolides 1-6 were isolated. The structures were elucidated by chemical methods and spectroscopic analysis. Compounds 1 and 4 exhibited activity against Artemia salina larvae.

Cyclosporine A amplifies Ca2+ signaling pathway in LLC-PK1 cells through the inhibition of plasma membrane Ca2+ pump

Cyclosporine A (CsA), a neutral, highly hydrophobic cyclic peptide with 11 amino acids, is currently the most widely used immunosuppressive drug for preventing graft rejection and autoimmune diseases. Despite its efficacy, the use of CsA is limited by severe side effects, mainly nephrotoxicity and arterial hypertension. Single cell microfluorimetry was used to evaluate the role of CsA on Ca(2+) signaling pathway in intact cells of the porcine proximal tubule-like cell line LLC-PK1; the assay of the in vitro activity of the plasma membrane Ca(2+) pump (PMCA) was carried out through the preparation and isolation of membranes. The addition of CsA to incubation medium at doses ranging from 0.1 to 2 microM did not change the basal level of intracellular calcium ([Ca(2+)](i)), whereas it affected the [Ca(2+)](i) response to thapsigargin (TG), a powerful inhibitor of microsomal Ca(2+) pump. In control studies, 5 microM TG produced a biphasic response: [Ca(2+)](i) peaked with a 60-s lag, and it then declined to a plateau of elevated [Ca(2+)](i), which remains above basal. However, it became evident that CsA strengthened the Ca(2+) response to TG because the addition of 5 microM TG to cells exposed to 400 nM CsA did not affect the peak response to TG, but it markedly affected the subsequent sustained phase ([Ca(2+)](i) = 156 +/- 4.84 versus 130 +/- 3.28 nmol, mean +/- SEM, n = 6, P < 0.001). In membrane preparations, 200 nM CsA brought about, in the presence of 10 microM calmodulin (CaM), a significant decrease of plasma membrane Ca(2+) pump (PMCA) activity (46.96 +/- 0.26 versus 53.48 +/- 1.96 nmol x mg of protein(-1) x min(-1), n = 6, P < 0.02), a value similar to that obtained in the presence of equimolar amounts of cyclosporine H (CsH), a non-immunosuppressive analogue of CsA. These findings suggest that in this cell line CsA affects the Ca(2+) export pathway through the reduction of the PMCA activity with consequent amplification and strengthening of [Ca(2+)](i) response after exposure to agents that trigger intracellular Ca(2+) release. The increased cell sensitivity during Ca(2+) signaling events ensuing from the impairment of this "defense system" may be regarded as one of the basic mechanisms involved in the development of the side effects induced by CsA.

2-aminoethoxydiphenyl borane activates a novel calcium-permeable cation channel

The membrane-permeable, noncompetitive inositol 1,4,5-trisphosphate (IP3)-receptor inhibitor 2-aminoethoxydiphenyl borane (2-APB) has been widely used to probe for IP3-receptor involvement in calcium signaling pathways. However, a number of recent studies in different cell types revealed other sites of action of 2-APB. In this study, we examined the influence of 2-APB on capacitative calcium entry and intracellular Ca2+ concentrations in rat basophilic leukemia (RBL-2H3 m1) cells. 2-APB was found to inhibit capacitative calcium entry, but at concentrations greater than 50 microM, a new effect of 2-APB was observed. When capacitative calcium entry was blocked with Gd3+, 2-APB caused an increase in cytoplasmic Ca2+. This increase in intracellular Ca2+ was not caused by altered buffering of cytoplasmic Ca2+ and was not caused by or in any way affected by the depletion of intracellular Ca2+ stores. Associated with the increase in intracellular Ca2+, in the presence of 2 mM Ca2+, 2-APB activated single channels in the plasma membrane with a conductance of approximately 50 pS. These channels seem to be nonselective cation channels; monovalent cations are the major carriers of current, but finite permeability to Ca2+ leads to a significant intracellular Ca2+ signal. Experiments with excised patches indicate that 2-APB activates these channels from the outer aspect of the cell membrane. This effect of 2-APB further illustrates the complex actions of this compound and reveals the presence in RBL-2H3 m1 cells of a novel, ligand-gated calcium-permeable channel.

Intracellular calcium release resulting from mGluR1 receptor activation modulates GABAA currents in wide-field retinal amacrine cells: a study with caffeine

The modulatory action of calcium (Ca2+) released from intracellular stores on GABAA receptor-mediated current was investigated in wide-field amacrine cells isolated from the teleost, Morone chrysops, retina. Caffeine, ryanodine or inositol 1,4,5-triphosphate (IP3) markedly inhibited the GABAA current by elevating [Ca2+]i. The inhibition resulted from the activation of a Ca2+--> Ca2+/calmodulin --> calcineurin cascade. Long (>12 s) exposure to glutamate mimicked the caffeine effect, i.e. it inhibited the GABAA current by elevating [Ca2+]i through mGluR1 receptor activation and consequent IP3 generation. This pathway provides a 'timed' disinhibitory mechanism to potentiate excitatory postsynaptic potentials in wide-field amacrine cells. It occurs as a result of the suppression of GABA-mediated conductances as a function of the duration of presynaptic excitatory input activity. This is much like some forms of long-term potentiation in the central nervous system. In a local retinal circuit this will selectively accentuate particular excitatory inputs to the wide-field amacrine cell. Similar to other neural systems, we suggest that activity-dependent postsynaptic disinhibition is an important feature of the signal processing in the inner retina.

Norepinephrine induces slow calcium signalling in murine brown preadipocytes through the beta-adrenoceptor/cAMP/protein kinase A pathway

The mechanism of adrenergically activated calcium signalling in isolated murine brown preadipocytes (stromal-vascular fraction) was studied with Fura-2. Norepinephrine (NE) generated in preadipocytes a slow Ca(2+)-response ( approximately 10 nM/min) without a burst and a maximum, whereas in mature brown adipocytes, the quick burst reached 1.5 microM [Ca(2+)](i). Thapsigargin, which is known to discharge Ca(2+) ions from the IP(3)-sensitive stores, initiated a huge capacitative calcium entry in mature brown adipocytes but failed to stimulate a response in preadipocytes. The beta-selective antagonist nadolol almost completely prevented the effect of NE on [Ca(2+)](i), while the antagonist of alpha-adrenoceptors phentolamine caused only a approximately 25% reduction of the cellular response. Forskolin or the cell-permeable Br-cAMP caused [Ca(2+)](i) rise, which were even higher than with NE. The protein kinase A (PKA) inhibitor N-[2-(p-bromocynnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89) reduced and the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine (IBMX), N-cyclohexyl-N-(2-hydroxyethyl)-4-(6-(1,2-dihydro-2-oxoquinolyloxy))butyramide (OPC-3911), 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidone (Ro 20-1724) or the protein phosphatase inhibitor okadaic acid enhanced the NE-, isoproterenol- or forskolin-initiated cellular calcium responses. It was concluded that (i) brown preadipocytes lacked a trigger mechanism of initiation of [Ca(2+)](i) rises and (ii) the cAMP- and protein kinase A-mediated phosphorylation played an important role in the beta-adrenoceptor-initiated calcium signalling in these cells. All these features distinguish brown adipocyte precursors from differentiated brown adipocytes, where calcium signalling is initiated exclusively via alpha(1)-adrenoceptors and the trigger mechanism.

Stretch-induced Ca(2+) release via an IP(3)-insensitive Ca(2+) channel

Various mechanical stimuli increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) in vascular smooth muscle cells (VSMC). A part of the increase in [Ca(2+)](i) is due to the release of Ca(2+) from intracellular stores. We have investigated the effect of mechanical stimulation produced by cyclical stretch on the release of Ca(2+) from the intracellular stores. Permeabilized VSMC loaded with (45)Ca(2+) were subjected to 7.5% average (15% maximal) cyclical stretch. This resulted in an increase in (45)Ca(2+) rate constant by 0.126 +/- 0.0035. Inhibition of inositol 1,4,5-trisphosphate (IP(3)), ryanodine, and nicotinic acid adenine dinucleotide phosphate channels (NAADP) with 50 microg/ml heparin, 50 microM ruthenium red, and 25 microM thio-NADP, respectively, did not block the increase in (45)Ca(2+) efflux in response to cyclical stretch. However, 10 microM lanthanum, 10 microM gadolinium, and 10 microM cytochalasin D but not 10 microM nocodazole inhibited the increase in (45)Ca(2+) efflux. This supports the existence of a novel stretch-sensitive intracellular Ca(2+) store in VSMC that is distinct from the IP(3)-, ryanodine-, and NAADP-sensitive stores.

Effect of dialkyl phthalates on the degranulation and Ca2+ response of RBL-2H3 mast cells

We examined the effect of three dialkyl phthalates, di-n-butylphthalate (DBP), di-isobutylphthalate (DIBP) and di(2-ethylhexyl)phthalate (DEHP), on antigen-induced degranulation of RBL-2H3 mast cells. Exposure to 50-500 microM DBP, 50-500 microM DIBP, and 500 microM DEHP significantly potentiated antigen-induced beta-hexosaminidase release. Without antigen stimulation, the phthalates did not cause any significant increase in degranulation. Next, we examined the Ca2+ response of RBL-2H3 cells after exposure to these phthalates. The cytosolic calcium ion concentration ([Ca2+]i) of the cells clearly increased when the cells were stimulated with 50-500 microM and 50-500 microM DIBP, and increased slightly when stimulated with 50-500 microM DEHP. Digital imaging fluorescence microscope analysis showed that the addition of DBP evoked Ca2+ oscillation in individual mast cells. Finally, we investigated the relationship between the DBP-sensitive Ca2+ stores and thapsigargin (TG)-sensitive Ca2+ stores. A rise in [Ca2+](i) following challenge with DBP after TG was observed, and thus the DBP-sensitive and TG-sensitive Ca2+ stores in RBL-2H3 cells seem to be different. In conclusion, some dialkyl phthalates increase antigen-induced degranulation in RBL-2H3 cells dependent on the increase of [Ca2+]i.

PKC- and ERK-dependent activation of I kappa B kinase by lipopolysaccharide in macrophages: enhancement by P2Y receptor-mediated CaMK activation

1. Although accumulating studies have identified I kappa B kinase (IKK) to be essential for controlling NF-kappa B activity in response to several cytokines, the upstream kinases that control IKK activity are still not completely known. We have previously reported that G protein-coupled P2Y(6) receptor activation by UTP potentiates lipopolysaccharide (LPS)-induced I kappa B phosphorylation and degradation, and NF-kappa B activation in J774 macrophages. In this study, we investigated the upstream kinases for IKK activation by UTP and LPS. 2. In murine J774 macrophages, LPS-induced NF-kappa B activation was inhibited by the presence of PDTC, D609, Ro 31-8220, PD 098059 and SB 203580. 3. Accompanying NF-kappa B activation, LPS induced I kappa B degradation and IKK activation were reduced by PDTC, D609, Ro 31-8220 and PD 098059, but not by SB 203580. 4. Although UTP itself slightly induced IKK activation, this response was synergistic with LPS. BAPTA/AM and KN-93 (a calcium/calmodulin-dependent protein kinase (CaMK) inhibitor) attenuated UTP- but not LPS-stimulated IKK activity. Synergistic IKK activation between LPS and thapsigargin was further demonstrated in peritoneal macrophages. 5. LPS and UTP co-stimulation additively increased p65 NF-kappa B phosphorylation. In vitro kinase assays revealed that LPS and UTP induced extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase activation were respectively inhibited by PD098059 and SB 203580. 6. Taken together, we demonstration that Gq protein-coupled P2Y(6) receptor activation can potentiate LPS-stimulated IKK activity. While PKC and ERK participate in IKK activation by LPS and UTP, the phosphatidylinositide-phospholipase C-dependent activation of CaMK plays a major role in UTP potentiation of the LPS response.

Cellular mechanisms underlying temperature-induced bleaching in the tropical sea anemone Aiptasia pulchella

Temperature-induced bleaching in symbiotic cnidarians is a result of the detachment and loss of host cells containing symbiotic algae. We tested the hypothesis that host cell detachment is evoked through a membrane thermotropic event causing an increase in intracellular calcium concentration, [Ca2+]i, which could then cause collapse of the cytoskeleton and perturb cell adhesion. Electron paramagnetic resonance measurements of plasma membranes from the tropical sea anemone Aiptasia pulchella and the Hawaiian coral Pocillopora damicornis labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) revealed no membrane thermotropic event. In addition, intracellular imaging using Fura-2AM as well as labeling anemones with 45Ca revealed no significant change in [Ca2+]i. However, bleaching could be evoked at ambient temperature with 25 mmol l–1 caffeine without affecting [Ca2+]i. [Ca2+]i could be altered with ionomycin in isolated host cells, but ionomycin could not induce bleaching in A. pulchella. As caffeine can affect levels of intracellular protein phosphorylation, the ability of other agents that alter intracellular levels of protein phosphorylation to evoke bleaching was investigated. The protein phosphatase inhibitor vanadate could induce bleaching in A. pulchella. Two-dimensional gels of 32P-labeled proteins from cold-shocked, caffeine-treated and control anemones show that both temperature shock and caffeine alter the array of phosphorylated host soluble proteins. We conclude that cnidarian bleaching is linked to a temperature-induced alteration in protein phosphorylation.