Transmembrane Calcium Flux Research Articles

Conditions of limited calcium influx (CLCI) inhibits IL2 induction and favors expression of anergy-related genes in TCR/CD3 and CD28 costimulated primary human T cells

Calcium is a key regulator of the T cell immune response. Depending on the spatial properties (nucleus versus cytoplasm) of the calcium signals generated after CD3xCD28 stimulation, primary human T cells either mount a productive immune response or develop tolerance. Nuclear calcium acts as a genomic decision maker: during T cell activation, it drives expression of genes associated with a productive immune response while in its absence, stimulated T cells acquire an anergy-like gene profile. Selective inhibition of nuclear calcium signaling in stimulated T cells blocks the productive immune response and directs the cells towards an anergy-like state. Here we show that the two transcriptional programs that include, respectively, the ‘activation gene’, interleukin 2 (IL2) and ‘anergy-related genes’, EGR2, EGR3, and CREM have different requirements for transmembrane calcium flux. By either lowering extracellular calcium concentrations with EGTA or using low concentrations of the ORAI blockers, BTP2 or RO2959, we reduced transmembrane calcium flux in human primary T cells stimulated with CD3xCD28. These ‘conditions of limited calcium influx’ (CLCI) blocked CD3xCD28-induced IL2 expression but only moderately affected induction of the anergy-related genes EGR2, EGR3, and CREM. We observed no difference in NFAT2 nuclear translocation after CD3xCD28 stimulation between normal conditions and CLCI. These results indicate that CLCI favors expression of anergy-related genes in activated human T cells. CLCI may be used to develop novel means for pro-tolerance immunosuppressive treatments.

K(+) regulates Ca(2+) to drive inflammasome signaling: dynamic visualization of ion flux in live cells.

P2X7 purinergic receptor engagement with extracellular ATP induces transmembrane potassium and calcium flux resulting in assembly of the NLRP3 inflammasome in LPS-primed macrophages. The role of potassium and calcium in inflammasome regulation is not well understood, largely due to limitations in existing methods for interrogating potassium in real time. The use of KS6, a novel sensor for selective and sensitive dynamic visualization of intracellular potassium flux in live cells, multiplexed with the intracellular calcium sensor Fluo-4, revealed a coordinated relationship between potassium and calcium. Interestingly, the mitochondrial potassium pool was mobilized in a P2X7 signaling, and ATP dose-dependent manner, suggesting a role for mitochondrial sensing of cytosolic ion perturbation. Through treatment with extracellular potassium we found that potassium efflux was necessary to permit sustained calcium entry, but not transient calcium flux from intracellular stores. Further, intracellular calcium chelation with BAPTA-AM indicated that P2X7-induced potassium depletion was independent of calcium mobilization. This evidence suggests that both potassium efflux and calcium influx are necessary for mitochondrial reactive oxygen generation upstream of NLRP3 inflammasome assembly and pyroptotic cell death. We propose a model wherein potassium efflux is necessary for calcium influx, resulting in mitochondrial reactive oxygen generation to trigger the NLRP3 inflammasome.

Genetic Evidence Supporting Caveolae Microdomain Regulation of Calcium Entry in Endothelial Cells

Various cellular signals initiate calcium entry into cells, and there is evidence that lipid rafts and caveolae may concentrate proteins that regulate transmembrane calcium fluxes. Here, using mice deficient in caveolin-1 (Cav-1) and Cav-1 knock-out reconstituted with endothelium-specific Cav-1, we show that Cav-1 is essential for calcium entry in endothelial cells and governs the localization and protein-protein interactions between transient receptor channels C4 and C1. Thus, Cav-1 is required for calcium entry in vascular endothelial cells and perhaps other specialized cell types containing caveolae.

Phospholemman and the Cardiac Sodium Pump

See related article, pages 1376–1383 In excitable tissues, the activity of the plasmalemmal sodium/potassium ATPase (Na/K pump) is vital for the maintenance of normal electrical activity and ion gradients. In cardiac muscle, the transsarcolemmal sodium (Na) gradient established by the Na/K activity is essential not only for generating the rapid upstroke of the action potential but also for driving a number of ion exchange and transport processes that are crucial for normal cellular function, excitation contraction coupling, ion homeostasis and the control of cell volume. These Na-dependent membrane transporters include those responsible for the regulation of other ions (such as the sodium calcium exchanger (NCX), Na/H exchanger and Na-HCO3 cotransporter), as well as those involved in the movement of substrates and amino acids.1 By determining the set point for NCX, the Na/K pump controls the predominant mechanism of transmembrane calcium (Ca) flux, and hence indirectly controls intracellular Ca load and myocardial contractility. Interventions that influence either the activity of the Na/K pump, or indirectly the transmembrane sodium gradient, can therefore profoundly affect normal cardiac function. Phospholemman, a type 1 transmembrane protein, is the predominant quantitative site of phosphorylation by protein kinase A (PKA) and protein kinase C (PKC) in cardiac sarcolemma.2 PKA phosphorylates serine 68 and PKC phosphorylates serines 63 and 68 in phospholemman. For a long time following its cloning in 1991,3 the physiological role of phospholemman was unclear. Indeed, writing in this journal in 1998, researchers noted that “As a major target for hormone-stimulated phosphorylation in the heart, the physiological function of phospholemman is likely to be an important one”,4 however they were unable to suggest what this function may be. Various roles have now been proposed: 1) regulation of cell volume; …

Voltage-gated cation channel modulators for the treatment of stroke

Neuronal voltage-gated cation channels regulate the transmembrane flux of calcium, sodium and potassium. Neuronal ischaemia occurring during acute ischaemic stroke results in the breakdown in the normal function of these ion channels, contributing to a series of pathological events leading to cell death. A dramatic increase in the intracellular concentration of calcium during neuronal ischaemia plays a particularly important role in the neurotoxic cascade resulting in stroke-related acute neurodegeneration. One approach to provide therapeutic benefit following ischaemic stroke has been to target neuronal voltage-gated cation channels, and particularly blockers of calcium and sodium channels, for post-stroke neuroprotection. A recent development has been the identification of openers of large-conductance calcium- and voltage-dependent potassium channels (maxi-K channels), which hyperpolarise ischaemic neurons, reduce excitatory amino acid release, and reduce ischaemic calcium entry. Thus far, targeting these voltage-gated cation channels has not yet yielded significant clinical benefit. The reasons for this may involve the lack of small-molecule blockers of many neuronal members of these ion channel families and the design of preclinical stroke models, which do not adequately emulate the clinical condition and hence lack sufficient rigor to predict efficacy in human stroke. Furthermore, there may be a need for changes in clinical trial designs to optimise the selection of patients and the course of drug treatment to protect neurons during all periods of potential neuronal sensitivity to neuro-protectants. Clinical trials may also have to be powered to detect small effect sizes or be focused on patients more likely to respond to a particular therapy. The development of future solutions to these problems should result in an improved probability of success for the treatment of stroke.

Targeting of Endothelial Nitric-oxide Synthase to the Cytoplasmic Face of the Golgi Complex or Plasma Membrane Regulates Akt- Versus Calcium-dependent Mechanisms for Nitric Oxide Release

The heterogeneous localization of endothelial nitricoxide synthase (eNOS) on the Golgi complex versus the plasma membrane has made it difficult to dissect the regulation of each pool of enzyme. Here, we generated fusion proteins that specifically target the plasma membrane or cytoplasmic aspects of the Golgi complex and have assessed eNOS activation. Plasma membrane-targeted eNOS constructs were constitutively active, phosphorylated, and responsive to transmembrane calcium fluxes, yet were insensitive to further activation by Akt-mediated phosphorylation. In contrast, cis-Golgi complex-targeted eNOS behaved similarly to wild-type eNOS and was less sensitive to calcium-dependent activation and highly responsive to Akt-dependent phosphorylation compared with plasma membrane versions. In plasma membrane- and Golgi complex-targeted constructs, Ser1179 is critical for NO production. This study provides clear evidence for functional roles of plasma membrane- and Golgi complex-localized eNOS and supports the concept that proteins thought to be regulated and to function exclusively in the plasma membrane of cells can indeed signal and be regulated in internal Golgi membranes.

Functional separation of deep cytoplasmic calcium from subplasmalemmal space calcium in cultured human uterine smooth muscle cells

For smooth muscle, two important functions of free intracellular calcium (Ca 2+ i) are modulation of plasma membrane excitability properties and modulation of the contractile apparatus. As proposed by van Breemen, Ca 2+ i can be divided into the subplasmalemmal space (Ca 2+ sps) and the deep cytosol (Ca 2+ d) by the superficial calcium buffer barrier. Using these distinctions, Ca 2+ sps activates the large conductance calcium-activated potassium channel (BK), and Ca 2+ d binds calcium-dependent fluorescent probes in the cytoplasm. We present here combined fluorescence—patch clamp experiments designed to simultaneously assess Ca 2+ d and Ca 2+ sps in cultured human uterine smooth muscle cells. Open probabilities ( P o) of the BK channel were measured using the cell-attached patch clamp technique. P o was used to approximate changes of [Ca 2+ sps]. Relative concentrations of Ca 2+ d were approximated by observing fluorescence of Calcium green-1 ( F). Under control conditions, we found similar time courses for rises of P o and F following 10 nM oxytocin (OT) addition. In parallel experiments, but with lanthanum (La 3+) added to the bath to block transmembrane calcium flux, P o was only slightly affected, but F increases were delayed and blunted. These data paradoxically indicate that following OT stimulation, the primary source of calcium for Ca 2+ sps is internal stores, and calcium entry from the extracellular space is required to raise Ca 2+ d. When cells were exposed to cyclopiazonic acid (CPA) to release SR calcium stores, P o increased slowly, then persisted at large values. The persistence of P o rises suggests that removal of calcium from the subplasmalemmal space is primarily via reuptake into the SR. In the presence of La 3+, OT-induced rises of F were slightly prolonged, suggesting that transmembrane calcium flux contributes to decreasing Ca 2+ d, but is not the primary mechanism. In summary, these data demonstrate that Ca 2+ d and Ca 2+ sps are not always intimately linked, but indicate a functional separation of the deep cytosol and the subplasmalemmal space that is consistent with the existence of a barrier to calcium diffusion between these two regions.

Oilgomerization characteristics of cysteine string protein

CSP function is vital to synaptic transmission, however; the precise nature of its role remains controversial. Conflicting reports support either a role for CSP: (i) in exocytosis or (ii) in the regulation of transmembrane calcium fluxes. Here we have examined the self-association of CSP to form oligomers that are stable upon SDS–PAGE. To understand the structural requirements for CSP self-association a series of CSP deletion mutants were constructed, expressed, and purified. This analysis revealed an interesting pattern of oligomerization. Amino acids between 83 and 136 were observed to be important for self-association. The recombinant CSP oligomers as well as the CSP monomers directly associate with Ni 2+–NTA agarose. Thus CSP–CSP interactions may be an important consideration for current working models of CSP chaperone activity at the synapse.

Potassium Channels and Human Corporeal Smooth Muscle Cell Tone: Diabetes and Relaxation of Human Corpus Cavernosum Smooth Muscle by Adenosine Triphosphate Sensitive Potassium Channel Openers

Sustained contraction of human corporeal smooth muscle depends on continuous transmembrane calcium flux through voltage gated calcium channels. K channels modulate corporeal smooth muscle membrane potential and, thus, ultimately affect transmembrane calcium flux. Therefore, we characterized relaxation responses elicited by the K channel modulators pinacidil and levcromakalim on isolated human corporeal tissue strips. We also evaluated the possibility that there may be alterations in adenosine triphosphate sensitive K channel pharmacology/function related to the presence of diabetes mellitus. A total of 215 isolated human corporeal tissue strips obtained from 57 male patients with organic erectile dysfunction were investigated. Cumulative concentration-response curves were constructed at half log increments for steady state relaxation responses elicited by pinacidil and levcromakalim on equivalently phenylephrine pre-contracted (to approximately 75% of maximum) isolated corporeal tissue strips. Potassium currents were measured using the cell attached whole cell patch clamp technique on freshly isolated corporeal smooth muscle cells. A concentration dependent, glibenclamide sensitive relaxation response of phenylephrine pre-contracted corporeal tissue strips was observed for pinacidil and levcromakalim. Consistent with such observations, electrophysiological recordings on freshly isolated myocytes revealed that pinacidil (10 microM.) and levcromakalim (10 microM.) induced whole cell potassium currents that were blocked by glibenclamide (10 microM.). In addition, statistical analysis revealed that phenylephrine pre-contracted corporeal tissue strips from patients without diabetes were more sensitive to relaxation by both compounds than corporeal tissue strips excised from those with diabetes. Furthermore, relaxation responses elicited by pinacidil and levcromakalim were not affected by charybdotoxin or 4-aminopyridine but were completely reversed by KCl or tetraethylammonium chloride. These data indicate that the adenosine triphosphate sensitive K channel subtype is likely to have an important role in the relaxation of isolated corporeal tissue strips and, moreover, they are the molecular target for the K channel modulators/openers levcromakalim and pinacidil. Such observations are consistent with the supposition that alterations in the structure/function/activity of these potassium channels may underlie at least some aspects of observed diabetes related differences in tissue sensitivity to K channel modulators.

The virally encoded fungal toxin KP4 specifically blocks L-type voltage-gated calcium channels.

KP4 is a virally encoded fungal toxin secreted by the P4 killer strain of Ustilago maydis. Previous studies demonstrated that this toxin inhibits growth of the target fungal cells by blocking calcium uptake rather than forming channels, as had been suggested previously. Unexpectedly, this toxin was also shown to inhibit voltage-gated calcium channel activity in mammalian cells. We used whole-cell patch-clamp techniques to further characterize this activity against mammalian cells. KP4 is shown to specifically block L-type calcium channels with weak voltage dependence to the block. Because KP4 activity is abrogated by calcium, KP4 probably binds competitively with calcium to the channel exterior. Finally, it is shown that chemical reagents that modify lysine residues reduce KP4 activity in both patch-clamp experiments on mammalian cells and in fungal killing assays. Because the only lysine residue is K42, this residue seems to be crucial for both mammalian and fungal channel activity. Our results defining the type of mammalian channel affected by this fungal toxin further support our contention that KP4 inhibits fungal growth by blocking transmembrane calcium flux through fungal calcium channels, and imply a high degree of structural homology between these fungal and mammalian calcium channels.

Effect of protein kinase C on transmembrane calcium fluxes in HaCaT keratinocytes

Capacitive calcium influx is associated with the release of calcium from internal stores and participates in intracellular calcium homeostasis. In keratinocytes, its activation is linked to the stimulation of the phospho-inositide (PI) pathway and seems to be altered in psoriasis. An overnight treatment of isolated HaCaT keratinocytes with phorbol 12-myristate 13-acetate (PMA) selectively downregulated the classical, calcium-dependent protein kinase C (PKC) isoenzyme PKC alpha in preconfluent cells. This was parallelled by an increased capacitative calcium influx with no effects on the PI pathway. These observations were strengthened in measurements using cyclopiazonic acid which revealed a 47% increase in PMA pretreated as compared with control cells in the calcium influx rate through store-operated calcium channels (SOC-s) following the emptying of the intracellular calcium stores. In confluent as compared with preconfluent cultures PKC epsilon was markedly increased, while other isoenzymes were not affected. In parallel, the kinetics of capacitative calcium influx were altered, showing clear inactivation. PMA pretreatment in these cells had little effect on PKC alpha but downregulated both PKC beta and PKC epsilon, and did not increase the influx through SOC-s. These observations support the differential regulation of SOC-s by PKC and suggest the involvement of several PKC isoenzymes in human keratinocytes.

The signaling mechanisms of long distance intercellular calcium waves (far waves) in cultured human uterine myocytes.

Cultured human myocytes exhibit intercellular calcium waves that travel farther than 100 microm ('far waves'). This work investigates the mechanism of far wave propagation. Culture lines were initiated from myometrial biopsies of term pregnant women. Calcium green-1 was used as a fluorescence probe for intracellular free calcium. Serial imaging was performed at a frame rate of 0.83 frames/s. Intercellular calcium waves were mechanically initiated by atraumatically applying small drops of mineral oil onto the surface of the monolayer. Each intercellular calcium wave was scored using a standardized grid, and points were assigned depending upon the distance the wave traveled and the fluorescent intensity observed within each region. Experiments were performed in the presence of inhibitors of gap junctions and connexin hemichannels (octanol), ATP (apyrase and MDL 12330 A), prostaglandins (indomethacin, high concentrations of lanthanum), the prostaglandin transporter, PGT (DIDS), and transmembrane calcium flux (low concentrations of lanthanum). Octanol, apyrase and MDL 12330 A failed to modify the far waves, indicating gap junctions, connexin hemichannels and ATP do not participate in the paracrine mechanism. Indomethacin at 30, 100 and 300 microM, in a dose dependent manner, reduced the far wave score to 0, suggesting a prostaglandin was critically involved in the mechanism. DIDS reduced the far wave score, but did not fully inhibit wave propagation, suggesting the presence of PGT-dependent and -independent components to the mechanism. Lanthanum at 0.1 mM had no effect, but at 1 mM, reduced the far wave score. These results are consistent with PGF2alpha and/or PGE2 being the signal molecule for the PGT-dependent component. Taken together, these data indicate that long distance intercellular calcium waves in cultured human myocytes utilizes a paracrine signaling mechanism, but with more than one extracellular signaling compound.

UNDERSTANDING MEMBRANE FUNCTION

Work on algae has had wide‐ranging impacts on our understanding of membrane function. Work on giant cells of freshwater and marine algae has been very important in defining and characterizing active transport systems for ions and other solutes and for studying other transport processes at the plasmalemma and tonoplast. Such work was particularly important in changing the focus of studies of higher plant membrane transport processes in the 1960s. Recent technical and genetic advances mean that studies formerly confined to large algal cells can now also be performed on higher plants and microalgae, but work on giant cells still makes important contributions. Studies on fucoid embryos continues to make significant contributions to our understanding of the role of transmembrane calcium fluxes in early development. This work has wide‐ranging implications for the development of other organisms.

INTEGRATIVE ERECTILE BIOLOGY: The Effects of Age and Disease on Gap Junctions and Ion Channels and Their Potential Value to the Treatment of Erectile Dysfunction

Initiation, maintenance, and modulation of corporal smooth muscle tone are critically dependent upon agonist-induced changes in intracellular calcium levels and mobilization as well as transmembrane calcium flux. The transient control of myocyte excitability and contractility at the cellular level is inextricably linked to membrane potential, which, in turn, is modulated by potassium ion efflux through one of the four known corporeal smooth muscle potassium ion channels. Corporal tissue responses are subsequently coordinated by means of the movement of intracellular second messenger molecules (i.e., IP3, cAMP, cGMP) and ions (i.e., K+ and Ca2+) among the corporal myocytes by means of intercellular communication through gap junction channels. Knowledge of the critical contribution of these interlinking cellular (nonjunctional ion channels [e.g., maxi-K]) and tissue (gap junction channels [e.g., connexin 43]) systems to the modulation of erectile capacity has provided the scientific rationale for the promulgation of the successful preclinical testing of hSlo ion channel gene therapy for the normalization of erectile status in both aged and diabetic rats.

A Plasticizer Released from IV Drip Chambers Elevates Calcium Levels in Neurosecretory Terminals

We report that intracellular calcium levels rise in mammalian neurosecretory terminals and in cultured pheochromocytoma cells during acute exposure to physiological medium incubated in IV drip chambers. The agent responsible for this effect is shown to be di(2-ethylhexyl)phthalate (DEHP). DEHP (800 nM) added to saline solution caused a rise in [Ca2+]i similar to that elicited by the contaminant-containing solution. The extraction of this contaminant from the IV drip chamber, as measured by spectrophotometry, was time-dependent and was markedly accelerated by the presence of 50 mM ethanol in the solution. Larger [Ca2+]i increases were observed in terminals exposed to solutions incubated in IV drip chambers for greater durations. The rise in calcium requires transmembrane calcium flux through membrane channels, as the response is blocked by either 100 μM cadmium or by lowering the extracellular free Ca2+ concentration to 10 μM. Our results suggest that acute alterations in intracellular calcium should be considered in addition to long-term effects when determining the safety of phthalate-containing plastics and that laboratory researchers using plastic perfusion materials consider this potential source of artifactual results.

Hormonal activation of phosphorylase in cockroach fat body trophocytes: A correlation with trans-membrane calcium flux.

This study is an investigation of the temporal relationship between transmembrane Ca(2+) fluxes, and glycogen phosphorylase activation in dispersed trophocytes from the fat body of the cockroach, Periplaneta americana. Phosphorylase is maximally activated within 5 min after treating the trophocytes with either of the hypertrehalosemic hormones, Pea-HTH-I and Pea-HTH-II. Activation caused by Pea-HTH-II is sustained for a longer period than that produced by Pea-HTH-I. Chelation of extracellular Ca(2+) with EGTA blocks the activation of phosphorylase by HTH. Similarly, chelation of intracellular Ca(2+) with Quin 2 greatly diminishes the phosphorylase activating effect of both HTHs. The data support the view that an increase in the intracellular Ca(2+ )concentration is required for the activation of phosphorylase and that extracellular Ca(2+) is an essential, although not necessarily sole, source of Ca(2+) for this purpose. Using (45)Ca(2+) to trace the movement of Ca(2+) following a challenge with either Pea-HTH-I or -II, it was shown that (45)Ca(2+)influx nearly doubled during the first 30 s. At this time, the trophocytes begin to expel Ca(2+) at a rate higher than that of untreated cells and this state persists for approximately 4 min. The Ca(2+) fluxes are consistent with its postulated role in the activation of phosphorylase. Arch.

Regulation of cardiac beta-adrenergic response by nitric oxide.

Time for primary review 12 days. The force and frequency of myocardial contraction are physiologically regulated by neurotransmitters and hormones. Norepinephrine released by the sympathetic nerves in the heart and epinephrine released into the circulation by adrenal glands increase myocardial contractility by acting on both α- and β-adrenergic receptors on heart muscle. Opposed to that is the action of acetylcholine released from parasympathetic nerves which reduces contractility by binding to muscarinic cholinergic receptors. The first demonstration that these two autonomic pathways are regulated by nitric oxide (NO) produced endogenously within cardiac muscle cells [1] both completes the understanding of the molecular mechanism of action of neurotransmitters in the heart and offers potential new therapeutic approaches for the correction of the altered responsiveness of cardiac muscle to autonomic regulation in circumstances such as heart failure. We will briefly review the molecular pathways leading to the intracellular actions of β-adrenergic and muscarinic cholinergic agonists in the cardiac myocyte, integrating the more recent evidence implicating the NO pathway from the single myocyte to clinical situations. ### 1.1 β-Adrenergic pathway β-Adrenergic agonists are well known to increase the force and frequency of contraction and increase the rate of relaxation of cardiac muscle. Despite some differences between regions of the heart, in general, the early increase in force of contraction is related directly to an increase in transmembrane flux of calcium, through phosphorylation of the L-type Ca channel, and the subsequent calcium-induced calcium release from the sarcoplasmic reticulum, whereas the sustained inotropic effect during the subsequent beats results from both increased influx and increased mobilization of internal calcium resulting from an increased replenishing of the reservoir of calcium in the sarcoplasmic reticulum [2,3]. A hallmark of the β-adrenergic effect on the heart is to increase the rate of relaxation which has been related to more rapid termination of … * Corresponding author. Tel.: +32-2-764-5349; fax: +32-2-764-9322 balligand{at}mint.ucl.ac.be

Calcium oscillations in rhythmically active respiratory neurones in the brainstem of the mouse.

1. The rhythmically active respiratory network in the brainstem slice of the mouse was investigated under in vitro conditions using patch clamp and microfluorometric techniques. Rhythmic respiratory activity persisted over the whole course of an experiment. 2. Electrophysiologically recorded rhythmic activity in respiratory neurones was accompanied by oscillations in intracellular calcium, which displayed a maximal concentration of 300 nM and decayed to basal levels with a mean time constant of 1.6 +/- 0.9 s. 3. Elevations of calcium concentrations were highly correlated with the amplitude of rhythmic membrane depolarization of neurones, indicating that they were initiated by a calcium influx across the plasma membrane through voltage-gated calcium channels. 4. Voltage clamp protocols activating either high voltage-activated (HVA) or both HVA and low voltage-activated (LVA) calcium channels showed that intracellular calcium responses were mainly evoked by calcium currents through HVA channels. 5. Somatic calcium signals depended linearly on transmembrane calcium fluxes, suggesting that calcium-induced calcium release did not substantially contribute to the response. 6. For calcium elevations below 1 microM, decay time constants were essentially independent of the amplitude of calcium rises, indicating that calcium extrusion was adequately approximated by a linear extrusion mechanism. 7. Cytosolic calcium oscillations observed in neurones of the ventral respiratory group provide further evidence for rhythmic activation of calcium-dependent conductances or second messenger systems participating in the generation and modulation of rhythmic activity in the central nervous system.

Cysteine-string proteins regulate exocytosis of insulin independent from transmembrane ion fluxes

Cysteine-string proteins (Csps) are vesicle proteins involved in exocytosis of synaptic vesicles in Drosophila and modulation of presynaptic calcium influx. As both the contribution of calcium channel regulation to the role of Csp in exocytosis and a function of Csp outside the nervous system are unknown, we studied its function in endocrine exocytosis from large dense core vesicles (LDCVs) using insulin-secreting pancreatic β-cells. Csps were expressed in primary and derived β-cell lines on insulin-containing LDCVs. Suppression of Csp expression reduced not only depolarisation induced insulin release but also exocytosis in permeabilised cells directly stimulated by Ca 2+. Thus, Csp is a secretory granule protein and is required for endocrine exocytosis independent of the modulation of transmembrane calcium fluxes.

Aspects of Lead Toxicity and Habituation in Hermissenda Learning.

Previous articleNext article No AccessNEUROBIOLOGYAspects of Lead Toxicity and Habituation in Hermissenda LearningA. M. Kuzirian, H. T. Epstein, and N. S. RaffertyA. M. Kuzirian Search for more articles by this author , H. T. Epstein Search for more articles by this author , and N. S. Rafferty Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Biological Bulletin Volume 193, Number 2October 1997 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv193n2p263 Views: 10Total views on this site Citations: 2Citations are reported from Crossref Copyright © 1997 by Marine Biological LaboratoryPDF download Crossref reports the following articles citing this article:A. M. Kuzirian, H. T. Epstein, T. J. Nelson, N. S. Rafferty, and D. L. Alkon Lead, Learning, and Calexcitin in Hermissenda, The Biological Bulletin 195, no.22 (Sep 2016): 198–201.https://doi.org/10.2307/1542837C. T. Tamse, K. Hammar, D. M. Porterfield, and P. J. S. Smith Transmembrane Calcium Flux in Pb+2-Exposed Aplysia Neurons, The Biological Bulletin 195, no.22 (Sep 2016): 201–202.https://doi.org/10.2307/1542838