Role Of Calcium Influx Research Articles

Relationship Between Vitamin D Status and Incidences of Falls Among the Elderly in Some South-Eastern Communities of Nigeria

<i>Background</i>: Vitamin D has been known to play an important role in musculoskeletal health. As a result, it is postulated that low vitamin D status is responsible for falls in the elderly due to the genomic role of the vitamin on Vitamin-D-receptors (VDR) in muscle cells and its non-genomic role in calcium influx into muscles. Hence, the present study aimed to establish the relationship between serum vitamin D levels and fall events in the elderly to reduce morbidity. <i>Methods</i>: It was a prospective, case-controlled, and cross-sectional study of 89 patients aged ≥ 60 years that had experienced at least one fall in the previous 12 months in three rural communities of Enugu State and their 124 age-matched controls. Serum 25(OH)D was assayed by enzyme-linked immune-sorbent assay and the number of falls was obtained from interviewer-administered questionnaires. Acquired data were analyzed using descriptive and comparative statistical methods. <i>Result</i>: The mean serum 25(OH)D level of patients was significantly lower than that of controls (patients 24.6±7.2 ng/mL versus controls 56.0±9.2 ng/mL; p=0.0001), and showed a significant negative correlation with the number of falls in the elderly (r=-0.347, p=0.002). Nevertheless, no significant difference in serum 25(OH)D levels of male and female patients and control groups was observed (p>0.05). There was a statistically increasing number of falls with increasing age and decreasing serum 25(OH)D levels (p=0.0001) among the patients. <i>Conclusion</i>: It can be concluded from this study that serum 25(OH)D level is inversely related to the number of falls experienced by the elderly irrespective of gender.

Englerin A-sensing charged residues for transient receptor potential canonical 5 channel activation.

The transient receptor potential canonical (TRPC) 5 channel, known as a nonselective cation channel, has a crucial role in calcium influx. TRPC5 has been reported to be activated by muscarinic receptor activation and extracellular pH change and inhibited by the protein kinase C pathway. Recent studies have also suggested that TRPC5 is extracellularly activated by englerin A (EA), but the mechanism remains unclear. The purpose of this study is to identify the EA-interaction sites in TRPC5 and thereby clarify the mechanism of TRPC5 activation. TRPC5 channels are over-expressed in human embryonic kidney (HEK293) cells. TRPC5 mutants were generated by site-directed mutagenesis. The whole-cell patch-clamp configuration was used to record TRPC5 currents. Western analysis was also performed to observe the expression of TRPC5 mutants. To identify the EA-interaction site in TRPC5, we first generated pore mutants. When screening the mutants with EA, we observed the EA-induced current increases of TRPC5 abolished in K554N, H594N, and E598Q mutants. The current increases of other mutants were reduced in different levels. We also examined the functional intactness of the mutants that had no effect by EA with TRPC5 agonists, such as carbachol or GTPγS. Our results suggest that the three residues, Lys-554, His-594, and Glu-598, in TRPC5 might be responsible for direct interaction with EA, inducing the channel activation. We also suggest that although other pore residues are not critical, they could partly contribute to the EA-induced channel activation.

Pneumolysin-Dependent Calpain Activation and Interleukin-1α Secretion in Macrophages Infected with Streptococcus pneumoniae.

Pneumolysin (PLY), a major virulence factor of Streptococcus pneumoniae, is a pore-forming cytolysin that modulates host innate responses contributing to host defense against and pathogenesis of pneumococcal infections. Interleukin-1α (IL-1α) has been shown to be involved in tissue damage in a pneumococcal pneumonia model; however, the mechanism by which this cytokine is produced during S. pneumoniae infection remains unclear. In this study, we examined the role of PLY in IL-1α production. Although the strains induced similar levels of pro-IL-1α expression, wild-type S. pneumoniae D39, but not a deletion mutant of the ply gene (Δply), induced the secretion of mature IL-1α from host macrophages, suggesting that PLY is critical for the maturation and secretion of IL-1α during S. pneumoniae infection. Further experiments with calcium chelators and calpain inhibitors indicated that extracellular calcium ions and calpains (calcium-dependent proteases) facilitated the maturation and secretion of IL-1α from D39-infected macrophages. Moreover, we found that PLY plays a critical role in calcium influx and calpain activation, as elevated intracellular calcium levels and the degradation of the calpain substrate α-fodrin were detected in macrophages infected with D39 but not the Δply strain. These results suggested that PLY induces the influx of calcium in S. pneumoniae-infected macrophages, followed by calpain activation and subsequent IL-1α maturation and secretion.

Endothelin A receptor blocker atrasentan lowers blood pressure by the reduction of nifedipine-sensitive calcium influx in Ren-2 transgenic rats fed a high-salt diet.

Our previous experiments demonstrated that selective endothelin A (ETA) receptor blockade had antihypertensive effects in Ren-2 transgenic rats (TGRs), but the mechanisms responsible for this change of blood pressure (BP) have not been explored yet. Four-week-old male heterozygous TGRs and their normotensive controls--Hannover Sprague-Dawley (HanSD) rats--were fed high-salt diet (2% NaCl) and were treated with selective ETA receptor blocker atrasentan (5 mg/kg per day) for 8 weeks. At the end of the study, the contribution of principle vasoactive systems was evaluated by the sequential blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium) and nitric oxide synthase [N-nitro-L-arginine methyl ester (L-NAME)]. The role of calcium influx through L-type voltage-dependent calcium channels in BP maintenance was evaluated using nifedipine. In a separate group of animals, the efficiency of distinct vasodilator systems--prostanoids (blocked by nonselective cyclooxygenase inhibitor indomethacin) and Ca-activated K channels (inhibited by tetraethylammonium)--was also analyzed. Atrasentan attenuated the development of hypertension in heterozygous TGRs, but had no effects in Hannover Sprague-Dawley rats. Moreover, atrasentan moderately attenuated renin-angiotensin system-dependent vasoconstriction, whereas it had no effect on sympathetic vasoconstriction. The nifedipine-sensitive BP component was markedly decreased by atrasentan treatment. In contrast, vasodilatation mediated by nitric oxide, endogenous prostanoids or Ca-activated K channels was reduced in atrasentan-treated TGRs, indicating the absence of compensatory augmentation of endothelin B receptor-mediated vasodilation in these animals. BP-lowering effect of chronic atrasentan treatment in TGRs was mainly caused by reduced Ca influx through L-type voltage-dependent calcium channels due to missing ETA receptor-dependent vasoconstriction and attenuated angiotensin II-dependent vasoconstriction.

Role of Calcium Influx and Modulation of Local Neurotransmitters as Hallmarks of Pediatric Traumatic Brain Injury - Retracted

This article was retracted on 09/11/2010.

Autocrine regulation of T‐cell activation by ATP release and P2X7receptors

T-cell activation requires the influx of extracellular calcium, although mechanistic details regarding such activation are not fully defined. Here, we show that P2X(7) receptors play a key role in calcium influx and downstream signaling events associated with the activation of T cells. By real-time PCR and immunohistochemistry, we find that Jurkat T cells and human CD4(+) T cells express abundant P2X(7) receptors. We show, using a novel fluorescent microscopy technique, that T-cell receptor (TCR) stimulation triggers the rapid release of ATP (<100 microM). This release of ATP is required for TCR-mediated calcium influx, NFAT activation, and interleukin-2 (IL-2) production. TCR activation up-regulates P2X(7) receptor gene expression. Removal of extracellular ATP by apyrase or alkaline phosphatase treatment, inhibition of ATP release with the maxi-anion channel blocker gadolinium chloride, or siRNA silencing of P2X(7) receptors blocks calcium entry and inhibits T-cell activation. Moreover, lymphocyte activation is impaired in C57BL/6 mice that express poorly functional P2X(7) receptors, compared to control BALB/c mice, which express fully functional P2X(7) receptors. We conclude that ATP release and autocrine, positive feedback through P2X(7) receptors is required for the effective activation of T cells.

P3-014: The role of calcium influx in ET-1-induced proliferation of human lung adenocarcinoma cells SPC-A1

P3-014: The role of calcium influx in ET-1-induced proliferation of human lung adenocarcinoma cells SPC-A1

Cell cycle-dependent regulation of store-operated I CRAC and Mg 2+-nucleotide-regulated MagNuM (TRPM7) currents

Calcium signaling is a central mechanism for numerous cellular functions and particularly relevant for immune cell proliferation. However, the role of calcium influx in mitotic cell cycle progression is largely unknown. We here report that proliferating rat mast cells RBL-2H3 tightly control their major store-operated calcium influx pathway, I CRAC, during cell cycle progression. While I CRAC is maintained at control levels during the first gap phase (G1), the current is significantly up-regulated in preparation for and during chromatin duplication. However, mitosis strongly suppresses I CRAC. Non-proliferating cells deprived of growth hormones strongly down-regulate I CRAC while increasing cell volume. We further show that the other known calcium (and magnesium) influx pathway in mast cells, the TRPM7-like magnesium-nucleotide-regulated metal (MagNuM) current, is largely uncoupled from cell cycle regulation except in G1. Taken together, our results demonstrate that both store-operated calcium influx via I CRAC and MagNuM are regulated at crucial checkpoints during cell cycle progression.

Voltage-dependent calcium influx mediates maturation of myofibril arrangement in ascidian larval muscle

Calcium signaling is important for multiple events during embryonic development. However, roles of calcium influx during embryogenesis have not been fully understood since routes of calcium influx are often redundant. To define roles of voltage-gated calcium channel (Cav) during embryogenesis, we have isolated an ascidian Cav β subunit gene (TuCavβ) and performed gene knockdown using the morpholino antisense oligonucleotide (MO). The suppression of Cav activity by TuCavβMO remarkably perturbed gastrulation and tail elongation. Further, larvae with normal morphology also failed to exhibit motility. Phalloidin-staining showed that arrangement of myofibrils was uncoordinated in muscle cells of TuCavβMO-injected larvae with normal tail. To further understand the roles of Cav activity in myofibrillogenesis, we tested pharmacological inhibitions with ryanodine, curare, and N-benzyl-p-toluensulphonamide (BTS). The treatment with ryanodine, an intracellular calcium release blocker, did not significantly affect the motility and establishment of the myofibril orientation. However, treatment with curare, an acetylcholine receptor blocker, and BTS, an actomyosin ATPase specific inhibitor, led to abnormal motility and irregular orientation of myofibrils that was similar to those of TuCavβMO-injected larvae. Our results suggest that contractile activation regulated by voltage-dependent calcium influx but not by intracellular calcium release is required for proper arrangement of myofibrils.

Role of calcium influx through voltage-operated calcium channels and of calcium mobilization in the physiology of Schistosoma mansoni muscle contractions

We tested the hypothesis that voltage-operated Ca2+ channels mediate an extracellular Ca2+ influx in muscle fibres from the human parasite Schistosoma mansoni and, along with Ca2+ mobilization from the sarcoplasmic reticulum, contribute to muscle contraction. Indeed, whole-cell voltage clamp revealed voltage-gated inward currents carried by divalent ions with a peak current elicited by steps to +20 mV (from a holding potential of -70 mV). Depolarization of the fibres by elevated extracellular K+ elicited contractions that were completely dependent on extracellular Ca2+ and inhibited by nicardipine (half inhibition at 4.1 microM). However these contractions were not very sensitive to other classical blockers of voltage-gated Ca2+ channels, indicating that the schistosome muscle channels have an atypical pharmacology when compared to their mammalian counterparts. Futhermore, the contraction induced by 5 mM caffeine was inhibited after depletion of the sarcoplasmic reticulum either with thapsigargin (10 microM) or ryanodine (10 microM). These data suggest that voltage-operated Ca2+ channels do contribute to S. mansoni contraction as does the mobilization of stored Ca2+, despite the small volume of sarcoplasmic reticulum in schistosome smooth muscles.

The immunobiology of Guillain‐Barré syndromes

This presentation highlights aspects of the immunobiology of the Guillain-Barré syndromes (GBS), the world's leading cause of acute autoimmune neuromuscular paralysis. Understanding the key pathophysiological pathways of GBS and developing rational, specific immunotherapies are essential steps towards improving the clinical outcome of this devastating disorder. Much of the research into GBS over the last decade has focused on the forms mediated by anti-ganglioside antibodies, and we have made substantial progress in our understanding in several related areas. Particular highlights include (a) the emerging correlations between anti-ganglioside antibodies and specific clinical phenotypes, notably between anti-GM1/anti-GD1a antibodies and the acute motor axonal variant and anti-GQ1b/anti-GT1a antibodies and the Miller Fisher syndrome; (b) the identification of molecular mimicry between GBS-associated Campylobacter jejuni oligosaccharides and GM1, GD1a, and GT1a gangliosides as a mechanism for anti-ganglioside antibody induction; (c) the development of rodent models of GBS with sensory ataxic or motor phenotypes induced by immunisation with GD1b or GM1 gangliosides, respectively. Our work has particularly studied the motor nerve terminal as a model site of injury, and through combined active and passive immunisation paradigms, we have developed murine neuropathy phenotypes mediated by anti-ganglioside antibodies. This has been achieved through use of glycosyltransferase and complement regulator knock-out mice, both for cloning anti-ganglioside antibodies and inducing disease. Through such studies, we have proven a neuropathogenic role for murine anti-ganglioside antibodies and human GBS-associated antisera and identified several determinants that influence disease expression including (a) the level of immunological tolerance to microbial glycans that mimic self-gangliosides; (b) the ganglioside density in target tissue; (c) the level of complement activation and the neuroprotective effects of endogenous complement regulators; and (d) the role of calcium influx through complement pores in mediating axonal injury. Such studies provide us with clear information on an antibody-mediated pathogenesis model for GBS and should lead to rational therapeutic testing of agents that are potentially suitable for use in humans.

Intracellular calcium signals and control of cell proliferation: how many mechanisms?

The progression through the cell cycle in non-transformed cells is under the strict control of extracellular signals called mitogens, that act by eliciting complex cascades of intracellular messengers. Among them, increases in cytosolic free calcium concentration have been long realized to play a crucial role; however, the mechanisms coupling membrane receptor activation to calcium signals are still only partially understood, as are the pathways of calcium entry in the cytosol. This article centers on the role of calcium influx from the extracellular medium in the control of proliferative processes, and reviews the current understanding of the pathways responsible for this influx and of the second messengers involved in their activation.

Confocal imaging of changes in glial calcium dynamics and homeostasis after mechanical injury in rat spinal cord white matter

Periaxonal glia play an important role in maintaining axonal function in white matter. However, little is known about the changes that occur in glial cells in situ immediately after traumatic injury. We used fluo-3 and confocal microscopy to examine the effects of localized (<0.5 mm) mechanical trauma on intracellular calcium (Ca i 2+) levels in glial cells in a mature rat spinal cord white matter preparation in vitro. At the injury site, the glial Ca i 2+ signal increased by 300–400% within 5 min and then irreversibly declined indicating cell lysis and death. In glial cells at sites adjacent to the injury (1.5–2 mm from epicenter), Ca i 2+ levels peaked at 10–15 min, and thereafter declined but remained significantly above rest levels. At distal sites (6–9 mm), Ca i 2+ levels rose and declined even slower, peaking at 80–90 min. Injury in zero calcium dampened Ca i 2+ responses, indicating a role for calcium influx in the generation and propagation of the injury-induced Ca i 2+ signal. By 50–80 min post-injury, surviving glial cells demonstrated an enhanced ability to withstand supraphysiological Ca i 2+ loads induced by the calcium ionophore A-23187. Glial fibrillary acidic protein (GFAP) and CNPase immunolabeling determined that the glial cells imaged with fluo-3 included both astrocytes and oligodendrocytes. These data provide the first direct evidence that the effects of localized mechanical trauma include a glial calcium signal that can spread along white matter tracts for up to 9 mm within less than 3 h. The results further show that trauma can enhance calcium regulation in surviving glial cells in the acute post-injury period.

Enhancement of alpha2-adrenoceptor-mediated vasoconstriction by the thromboxane-mimetic U46619 in the porcine isolated ear artery: role of the ERK-MAP kinase signal transduction cascade.

1. Alpha(2)-adrenoceptor-mediated contractions in porcine blood vessels can be enhanced in the presence of the thromboxane-mimetic U46619, and forskolin. The aim of this study was to determine the role of U46619 in the enhanced contractions, and to determine whether signalling through the ERK-MAP kinase pathway is involved. 2. Responses to the alpha(2)-adrenoceptor agonist UK14304 (1 micro M) were increased from 22+/-3% of the response to 60 mM KCl to 68+/-12% (n=8, mean+/-s.e.m.) in the presence of a low concentration of U46619 (< 20% of the 60 mM KCl response). 3. Both the direct and the U46619-enhanced UK14304 responses were inhibited by 50 microM PD98059, an inhibitor of the ERK-MAP kinase pathway. UK14304-induced contractions were associated with an increase in ERK2 phosphorylation, indicating an increased activity. In the presence of U46619, there was an enhanced phosphorylation of ERK2. U46619 on its own had no effect on ERK phosphorylation. 4. Both the direct and enhanced UK14304 contractions were inhibited in the absence of extracellular calcium. These conditions also prevented the increase in ERK2 phosphorylation. This indicates a role for calcium influx in the enhanced contractions. 5. In conclusion, this study demonstrates that precontraction with the thromboxane-mimetic U46619 enhances alpha(2)-adrenoceptor-mediated vasoconstriction through the enhancement of the ERK-MAP kinase pathway, and influx of extracellular calcium.

Lithium and KB-R7943 effects on mechanics and energetics of rat heart muscle.

The role of calcium influx on energy expenditure during cardiac contraction was studied. For this purpose, the described ability of lithium and KB-R 7943 (KBR) to diminish Ca entry through Na-Ca exchanger (Ponce-Hornos & Langer, J Mol Cell Cardiol 1980, 12, 1367, Satoh et al., Circulation 2000, 101, 1441) were used. In isolated contractions (contractions elicited after at least 5 min of rest) LiCl 45 mmol L(-1) decreased pressure developed and pressure-time integral from 42.3 +/- 2.7 and 14.5 +/- 1.2 to 32.1 +/- 3.4 mN mm(-2) and 8.3 +/- 0.9 mN mm(-2) s, respectively. A similar effect was observed in regular contractions (at 0.16 Hz stimulation). The presence of KBR (5 micromol L(-1)) in the perfusate induced a slight but not significant decrease in pressure developed and pressure-time integral in steady-state contractions. As it was previously described, the heat involved in a heart muscle contraction can be decomposed into several components (H1, H2, H3 and H4), but only one (H3) was associated with force generation. While H3 decreased with lithium in both types of contractions, H3/PtI ratio remained unaltered, indicating that the economy for pressure maintenance was unaffected. To further investigate the role of Ca entry on force development, a condition in which the contraction is mainly dependent on extracellular calcium was studied. An 'extra' stimulus applied 200 ms after the regular one in a muscle stimulated at 0.16 Hz induces a contraction with this characteristic (Marengo et al., Am J Physiol 1999, 276, H309). Lithium induced a strong decrease in pressure-time integral and H3 associated with this contraction (43 and 45%, respectively) with no change in H3/PtI ratio. Lithium also reduced (53%) an energy component (H2) associated with Ca cycling. The use of KBR showed qualitatively similar results [i.e. a 33% reduction in pressure-time integral associated with the extrasystole (ES) with no changes in H3/PtI ratio and a 30% reduction in the H2 component]. Li and KBR effects appear to be additive and in the presence of 45 mmol L(-1) Li and 5 micromol L(-1) KBR the extrasystole was abolished in 77%. Lithium and KBR effects particularly for the extrasystole can be explained through the inhibition of Ca entry via Na-Ca exchange giving support to the participation of the Na-Ca exchanger in the Ca influx from the extracellular space. In addition, the results also suggest the possibility of an effect of Li on an additional Ca sensitive locus (different than the Na-Ca exchanger). In this connection, in isolated contractions lithium decreased the energy release fraction related to mitochondrial processes (H4) increasing the economy of the overall cardiac contraction.

Role of Calcium Influx in Cytotoxic T Lymphocyte Lytic Granule Exocytosis during Target Cell Killing

One mechanism cytotoxic T lymphocytes use to kill targets is exocytosis of cytotoxic agents from lytic granules, a process that requires Ca 2+ influx. We investigated the role of Ca 2+ influx in granule exocytosis using TALL-104 human leukemic cytotoxic T cells triggered via a bispecific antibody containing an anti-CD3 F(ab′) to kill Raji B lymphoma cells. Using a novel fluorescence method, we detected target-directed release of ∼15% of lytic granules during killing. Consistent with previous work, we observed sustained CTL Ca 2+ gradients during killing, but gradients reflect the behavior of Fura-2 in granules. Rapid imaging experiments suggest that Ca 2+ channels are not polarized during killing, indicating that Ca 2+ influx does not direct granule reorientation. Furthermore, we find that Ca 2+ acts via a high-affinity interaction to promote granule exocytosis.

Death of rat sympathetic ganglion cells in vitro caused by neurite transection: effect of extracellular calcium.

Calcium entry into neurons secondary to excitotoxic insults is believed to cause neuronal death after trauma and ischemia, but the role of calcium influx in neuronal death after neurite transection independent of excitotoxicity has not been clearly defined. This study assesses the effect of variations in extracellular calcium concentration ([Ca2+]e) from 50 nM to 5 mM on cell death, in 14-day-old cultures of dissociated sympathetic neurons from the superior cervical ganglia of newborn rats. The neurites were transected with a custom-made injury device, and cell death was assessed with propidium iodide and fluorescence microscopy. We found that neurite transection caused a significant increase (p < 0.05) in cell death at all [Ca2+]e studies, but there was no significant difference in mortality at the various [Ca2+]e. Cell death significantly increased between 2 and 24 h postinjury at all three [Ca2+]e. Cell death increased with decreasing distance between the cell body and the transection site, and there was a significant decrease in mortality at distances greater than 0.66 mm, irrespective of the [Ca2+]e. These results suggest that influx of extracellular calcium is not responsible for posttransection cell death, suggesting that calcium release from internal stores or calcium-independent cell death mechanisms are triggered by neurite transection.

Up-regulation of GTP cyclohydrolase I and tetrahydrobiopterin by calcium influx.

GTP cyclohydrolase I (GTPCH) catalyzes the first and rate-limiting reaction in the synthesis of tetrahydrobiopterin (BH4), an obligatory co-factor for monoamines and nitric oxide syntheses. Roles of calcium influx on transcript, protein and activity levels of GTPCH and BH4 availability were studied using primary cultured bovine adrenal medullary cells. Bovine GTPCH cDNA was isolated and used in Northern blot analyses. Ionomycin, A23187 and BayK8644 dramatically up-regulated GTPCH mRNA level. Depolarization by potassium or veratridine also induced GTPCH expression, which was abolished by EGTA. A23187 elevated GTPCH protein level, enzyme activity, and BH4 levels. Thus, calcium influx up-regulates GTPCH gene expression and BH4 levels which may contribute to neurotoxicity directly and/or via elevation of dopamine and nitric oxide.

Regulation of the RhoA pathway in human endothelial cell spreading on type IV collagen: role of calcium influx.

We have shown that nonvoltage-operated Ca(2+) entry regulates human umbilical vein endothelial cell adhesion, migration, and proliferation on type IV collagen. We now demonstrate a requirement for Ca(2+) influx for activation of the RhoA pathway during endothelial cell spreading on type IV collagen. Reorganization of actin into stress fibers was complete when the cells where fully spread at 90 minutes. No actin organization into stress fibers was seen in endothelial cells plated on type I collagen, indicating a permissive effect of type IV collagen. CAI, a blocker of nonvoltage-operated Ca(2+) channels, prevented development of stress fiber formation in endothelial cells on type IV collagen. This permissive effect was augmented by Ca(2+) influx, as stimulated by 0. 5 microM thapsigargin or 0.1 microM ionomycin, yielding faster development of actin stress fibers. Ca(2+) influx and actin rearrangement in response to thapsigargin and ionomycin were abrogated by CAI. Activated, membrane-bound RhoA is a substrate for C3 exoenzyme which ADP-ribosylates and inactivates RhoA, preventing actin stress fiber formation. Pretreatment of endothelial cells with C3 exoenzyme prevented basal and thapsigargin-augmented stress fiber formation. While regulation of Ca(2+) influx did not alter RhoA translocation, it reduced in vitro ADP-ribosylation of RhoA (P(2)<0. 05), suggesting Ca(2+) influx is needed for RhoA activation during spreading on type IV collagen; no Ca(2+) regulated change in RhoA was seen in HUVECs spreading on type I collagen matrix. Blockade of Ca(2+) influx of HUVEC spread on type IV collagen also reduced tyrosine phosphorylation of p190Rho-GAP and blocked thapsigargin-enhanced binding of p190Rho-GAP to focal adhesion kinase. Thus, Ca(2+) influx is necessary for RhoA activation and for linkage of the RhoA/stress fiber cascade to the focal adhesion/focal adhesion kinase pathway during human umbilical vein endothelial cell spreading on type IV collagen.

Fast retrograde effects on neuronal death and dendritic organization in development: the role of calcium influx

Retrograde signals from axon terminal to cell body are known to regulate neuronal survival and differentiation during development. They are generally attributed to the uptake and transport of trophic factors, but there is recent evidence in the isthmo-optic nucleus for a remarkably fast-acting retrograde signal from the contralateral retina that is not mediated by the conventional trophic route. The isthmo-optic nucleus undergoes 55% neuron death between embryonic days 12 and 17, and becomes laminated at embryonic day 14 owing to dendritic re-organization. Blockade of retinal electrical activity just before day 14 reduces neuronal death and lamination in the isthmo-optic nucleus within as little as 6 h. We here investigate how action potentials initiate the fast-acting retrograde signal, and we provide evidence that the first step is calcium entry into the isthmo-optic axon terminals. Neuronal death and lamination are rapidly reduced in the isthmo-optic nucleus by intraocularly injected ω-conotoxin, a blocker of N-type calcium channels known to be located mainly on axon terminal. Similar effects occurred with two other calcium channel blockers (cadmium and α-bungarotoxin) believed to act on both the isthmo-optic terminals and their target cells, but not with nifedipine, a blocker of L-type (mainly somatic) channels, supporting a presynaptic initiation of the fast signal. Nevertheless postsynaptic events may also be involved because pharmacological destruction of the amacrine targets cells of the isthmo-optic nucleus reduced its cell death and lamination 9–12 h later.