scholarly journals The effects of microenvironment on the redifferentiation of regenerating neurones: neurite architecture, acetylcholine receptors and Ca2+ channel distribution

1987 ◽  
Vol 132 (1) ◽  
pp. 111-131
Author(s):  
M. E. Spira ◽  
D. Zeldes ◽  
B. Hochner ◽  
A. Dormann
Keyword(s):  
Action Potentials ◽  
Acetylcholine Receptors ◽  
Membrane Properties ◽  
Environmental Cues ◽  
Freezing And Thawing ◽  
Intrinsic Factors ◽  
Extrinsic Cues ◽  
Voltage Dependent ◽  
Synaptic Receptors ◽  
Ca2 Channels

Severed adult neurones, which are capable of regrowth, encounter different microenvironments from those encountered during development. Moreover, adult neurones may respond in a different manner from developing neurones to the same environmental cues. Thus, the recovery of the integrative and transmission capabilities (which depend on the neuronal architecture, passive and active membrane properties, and synaptic receptor distribution) by a regenerating adult neurone may not be complete. In the present review, we examine several aspects of the outcome of the interaction between the microenvironment and regrowing neurones using the cockroach giant interneurones (GINs) as a model system. We demonstrate that whereas extrinsic cues govern the morphological redifferentiation and distribution of synaptic receptors, the distribution of voltage-dependent Ca2+ channels is to a large extent determined by intrinsic factors. The pathway of regrowth and the architecture of regenerating GINs were studied by examination of intracellularly stained fibres. The environments provided by the connectives and ganglia are different. The elongating sprouts in the connective appeared as smooth cylinders. Within the ganglionic domain, the main longitudinal sprouts emitted neurites which extended and branched into the neuropile. The local cues for branching of neurites were eliminated by freezing and thawing of the ganglia prior to the arrival of the growing tips. The failure to extend neurites under these conditions is attributed to the elimination of extrinsic signals for morphological redifferentiation of the fibres, since the same fibres emit neurites in anterior ganglia which have not been subjected to freezing and thawing. The distribution of acetylcholine receptors (AChRs) on the GINs was mapped by ionophoretic application of ACh. In both the intact and regenerating GINs receptors were located only on the neurites. Freezing and thawing of a ganglion eliminated the local signals for insertion and/or activation of AChRs on the neurites. Thus, both the morphological redifferentiation and the distribution of AChRs are affected by the microenvironment. Voltage-dependent Ca2+ channels were detected after intracellular injection of tetraethylammonium into the GIN and in the presence of tetrodotoxin (TTX) and Ba2+ in the extracellular space. The regrowing axon tips always revealed large barium action potentials independent of the CNS microenvironment. This observation is consistent with the hypothesis that Ca2+ plays an important role in the growth process. However, increased Ba2+ responsiveness was also observed in axonal segments proximal to the region of neuronal extension.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of bromocriptine on prolactin release, electrical membrane properties and transmembrane Ca2+ fluxes in cultured rat pituitary adenoma cells

1986 ◽  
Vol 111 (2) ◽  
pp. 185-192 ◽  
Author(s):  
P. W. Johansen ◽  
O. Sand ◽  
J. G. Iversen ◽  
E. Haug ◽  
K. M. Gautvik
Keyword(s):  
Pituitary Adenoma ◽  
Action Potentials ◽  
Inhibitory Effect ◽  
Membrane Properties ◽  
Free Solution ◽  
Prolactin Release ◽  
Clonal Strain ◽  
Rat Pituitary ◽  
Basal Release ◽  
Voltage Dependent

Abstract. The effects of the dopamine (DA) agonist bromocriptine on prolactin (Prl) release, electrical membrane properties and transmembrane Ca2 + fluxes have been studied in a clonal strain of rat pituitary adenoma cells (GH3). These cells generate Ca2+ dependent action potentials, and produce and secrete spontaneously both Prl and growth hormone. Prl release stimulated by thyroliberin (TRH) and elevated extracellular K+ concentration was completely blocked by bromocriptine, whereas the basal release was only moderately affected. The TRH and K+ evoked Prl release were half maximally inhibited by bromocriptine at 5–10 and 10–50 μm, respectively. The normal biphasic membrane response to TRH and the depolarizing effect of elevated K+ concentration were not altered by bromocriptine, whereas the Ca2+-spikes in Na+-free solution were suppressed by the drug. We therefore suggest that bromocriptine blocks the voltage sensitive Ca2+-channels of GH3 cells. In agreement with this notion, bromocriptine also suppressed the basal and TRH induced 45Ca2+ efflux from preloaded cells. We conclude that the inhibitory effect of bromocriptine on the voltage dependent Ca2+-channels is an important mechanism responsible for suppression of Prl release.

scholarly journals Activation of AMPA/Kainate Receptors but Not Acetylcholine Receptors Causes Mg2+ Influx into Retzius Neurones of the Leech Hirudo medicinalis

2003 ◽  
Vol 122 (6) ◽  
pp. 727-739 ◽  
Author(s):  
Anja Müller ◽  
Dorothee Günzel ◽  
Wolf-Rüdiger Schlue
Keyword(s):  
Acetylcholine Receptors ◽  
Hirudo Medicinalis ◽  
Kainate Receptors ◽  
Cation Channels ◽  
Kainate Receptor ◽  
Intracellular Acidification ◽  
Voltage Dependent ◽  
Ionic Changes ◽  
Intracellular Signal ◽  
Ca2 Channels

In Retzius neurones of the medicinal leech, Hirudo medicinalis, kainate activates ionotropic glutamate receptors classified as AMPA/kainate receptors. Activation of the AMPA/kainate receptor–coupled cation channels evokes a marked depolarization, intracellular acidification, and increases in the intracellular concentrations of Na+ ([Na+]i) and Ca2+. Qualitatively similar changes are observed upon the application of carbachol, an activator of acetylcholine receptor-coupled cation channels. Using multibarrelled ion-selective microelectrodes it was demonstrated that kainate, but not carbachol, caused additional increases in the intracellular free Mg2+ concentration ([Mg2+]i). Experiments were designed to investigate whether this kainate-induced [Mg2+]i increase was due to a direct Mg2+ influx through the AMPA/kainate receptor–coupled cation channels or a secondary effect due to the depolarization or the ionic changes. It was found that: (a) Similar [Mg2+]i increases were evoked by the application of glutamate or aspartate. (b) All kainate-induced effects were inhibited by the glutamatergic antagonist DNQX. (c) The magnitude of the [Mg2+]i increases depended on the extracellular Mg2+ concentration. (d) A reduction of the extracellular Ca2+ concentration increased kainate-induced [Mg2+]i increases, excluding possible Ca2+ interference at the Mg2+-selective microelectrode or at intracellular buffer sites. (e) Neither depolarizations evoked by the application of 30 mM K+, nor [Na+]i increases induced by the inhibition of the Na+/K+ ATPase caused comparable [Mg2+]i increases. (f) Inhibitors of voltage-dependent Ca2+ channels did not affect the kainate-induced [Mg2+]i increases. Moreover, previous experiments had already shown that intracellular acidification evoked by the application of 20 mM propionate did not cause changes in [Mg2+]i. The results indicate that kainate-induced [Mg2+]i increases in leech Retzius neurones are due to an influx of extracellular Mg2+ through the AMPA/kainate receptor–coupled cation channel. Mg2+ may thus act as an intracellular signal to distinguish between glutamatergic and cholinergic activation of leech Retzius neurones.

scholarly journals Activation of Nicotinic Acetylcholine Receptors Augments Calcium Channel-mediated Exocytosis in Rat Pheochromocytoma (PC12) Cells

1998 ◽  
Vol 111 (2) ◽  
pp. 257-269 ◽  
Author(s):  
Amy B. Harkins ◽  
Aaron P. Fox
Keyword(s):  
Pc12 Cells ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Single Cells ◽  
Cellular Functions ◽  
Nicotinic Acetylcholine ◽  
Cellular Processes ◽  
Voltage Dependent ◽  
Vesicle Secretion ◽  
Ca2 Channels

The functional effect of activating Ca2+-permeable neuronal nicotinic acetylcholine receptors (nAChRs) on vesicle secretion was studied in PC12 cells. Single cells were patch-clamped in the whole-cell configuration and stimulated with either brief pulses of nicotine to activate the Ca2+-permeable nAChRs or with voltage steps to activate voltage-dependent Ca2+ channels. Membrane capacitance was used as a measure of vesicle secretion. Activation of nAChRs by nicotine application to cells voltage clamped at −80 mV evoked secretion. This secretion was completely abolished by nicotinic antagonists. When the cells were voltage clamped at +20 mV in the presence of Cd2+ to block voltage-activated Ca2+ channels, nicotine elicited a small amount of secretion. Most interestingly, when the nAChRs were activated coincidentally with voltage-dependent Ca2+ channels, secretion was augmented approximately twofold over the secretion elicited with voltage-dependent Ca2+ channels alone. Our data suggest that Ca2+ influx via nAChRs affects Ca2+-dependent cellular functions, including vesicle secretion. In addition to the secretion evoked by nAChR activation at hyperpolarized potentials, we demonstrate that even at depolarized potentials, nAChRs provide an important Ca2+ entry pathway underlying Ca2+-dependent cellular processes such as exocytosis.

Internal cesium ions block various K conductances in spinal motoneurons

1981 ◽  
Vol 59 (12) ◽  
pp. 1280-1284 ◽  
Author(s):  
E. Puil ◽  
R. Werman
Keyword(s):  
Action Potentials ◽  
Considerable Increase ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
Resting Potential ◽  
Large Reduction ◽  
Spinal Motoneurons ◽  
Spike Generation ◽  
Cesium Ions ◽  
Voltage Dependent

Conventional intracellular recording with low resistance electrodes was used to examine the effects of iontophoretic injections of Cs+ ions (30–200 nA for 30–500 s) into spinal motoneurons of cats anesthetized with pentobarbital and paralyzed with gallamine. The most striking effects of internal Cs+ were a great prolongation of the falling phase of action potentials, a large reduction in the amplitude of their afterhyperpolarizations, and a considerable increase in the size of delayed depolarizations. A reduction of resting membrane conductance (up to half of control values) and a small increase in membrane potential usually were evident. Although the rate of rise and amplitude of spikes sometimes were increased, the above effects on membrane properties usually were accompanied by block of antidromic invasion or synaptic spike generation, and inactivation of directly evoked spikes. Recovery of spike genesis was very rapid but the prolongation of spikes and other effects of Cs+ lasted 4–35 min, depending on the amount of Cs+ application. Larger injections of Cs+ resulted in greater depolarizations of up to 13 mV. It is concluded that internal Cs+ ions block voltage-dependent K+ conductance of spike repolarization, the Ca2+-activated K+ conductance responsible for the afterhyperpolarization, and some of the K+ conductance responsible for the resting potential. It is suggested that the enhanced delayed depolarization may result from a Cs+-blockade of an early outward K+ current which would unmask an inward current of Ca2+ ions.

Mechanisms for signal transformation in lemniscal auditory thalamus

1996 ◽  
Vol 76 (6) ◽  
pp. 3597-3608 ◽  
Author(s):  
F. Tennigkeit ◽  
D. W. Schwarz ◽  
E. Puil
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Membrane Properties ◽  
High Threshold ◽  
Tonic Firing ◽  
Sensory Stimuli ◽  
Current Pulses ◽  
Type K ◽  
Voltage Dependent ◽  
Medial Geniculate

1. During alertness, lemniscal thalamocortical neurons in the ventral medial geniculate body (MGBv) encode sound signals by firing action potentials in a tonic mode. When they are in a burst firing mode, characteristic of thalamic neurons during some sleep states, the same stimuli may have an alerting function, leading to conscious perception of sound. We investigated the intrinsic membrane properties of MGBv neurons in search of mechanisms that enable them to convert from burst to tonic firing modes, allowing accurate signal coding of sensory stimuli. 2. We studied thalamocortical relay neurons and identified neurons morphologically with injected N-(2-aminoethyl) biotinamide hydrochloride in in vitro slice preparations of young rats. With the use of the whole cell recording method, we examined the contributions of distinct conductances to voltage responses evoked by current pulses. The neurons (n = 74) displayed a narrow range of resting potentials (-68 +/- 4 mV, mean +/- SD) and an average input resistance of 226 +/- 100 M omega. The membrane time constant was 40 +/- 17.6 ms and the action potential threshold was -51.6 +/- 3 mV. 3. Injections of hyperpolarizing current pulses from rest revealed an inward rectification produced by two voltage-dependent components. A fast component, sensitive to blockade with Ba2+ (100–200 microM), was attributed to an inward rectifier, IIR. Such applications also increased input resistance and depolarized neurons, consistent with a blockade of various K+ conductances. Application of Ba2+ often unmasked another voltage-dependent rectification with a slower time course. The second component was sensitive to blockade with Cs+ (1.5 mM), reminiscent of a hyperpolarization-activated current, IH. 4. Depolarizing pulses from rest produced ramp-shaped voltage responses that led to delayed tonic firing. Blockade of Na+ conductances by tetrodotoxin (TTX, 300–600 nM), or extracellular replacement of Ca2+ with Mg2+ (with TTX present), reduced the slope of the ramp and the overall depolarizing response. Application of 4-aminopyridine (4-AP, 100 microM), a blocker of A-type K+ conductances, increased input resistance and the overall depolarizing response. The voltage ramp therefore represents a complex rectification due to voltage-dependent contributions of persistent Na-, Ca2+, and K+ conductances. 5. Depolarizing pulses from potentials of less than -75 mV evoked phasic burst responses, consisting of one to seven action potentials riding on a low-threshold spike (LTS). The LTS was absent in low extracellular Ca2+ conditions and was blocked by application of Ni2+ (0.6 mM), but not by Cd2+ (50 microM). Similar depolarization from less than -80 mV evoked several action potentials, often followed by a TTX-resistant high-threshold spike (HTS) of longer duration. Firing of HTSs always occurred during 4-AP (100 microM) application, inferring that, normally, A-type K+ conductances may control ability to fire an HTS. As in the LTS, a Ca2+ current is a major participant in the HTS because extracellular replacement of Ca2+ with Mg2+ or application of Cd2+ (50 microM) blocked its genesis. After TTX blockade of Na+ conductances, “tonic firing” of HTSs occurred during depolarization above -45 mV. 6. During tonic firing evoked by current pulses, the second and subsequent spikes were longer in duration than the initial action potentials. Low extracellular concentrations of Ca2+ or Cd2+ (50 microM) application reduced the durations of the nonprimary spikes, inferring a contribution of high-threshold voltage-dependent Ca2+ conductances to their repolarizing phase. Also, K+ conductances may contribute to spike repolarization, because 4-AP (100 microM) or tetraethylammonium (2 mM) application led to prolonged action potentials and the generation of plateau potentials. A fast afterhyperpolarization, likely mediated by a Ca(2+)-dependent K+ conductance, limited the tonic firing. Such conductances, therefore, may regulate the re

scholarly journals A native prokaryotic voltage-dependent calcium channel with a novel selectivity filter sequence

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Takushi Shimomura ◽  
Yoshiki Yonekawa ◽  
Hitoshi Nagura ◽  
Michihiro Tateyama ◽  
Yoshinori Fujiyoshi ◽  
...  
Keyword(s):  
Action Potentials ◽  
Negative Charge ◽  
Selectivity Filter ◽  
Na Channels ◽  
Glycine Residue ◽  
Voltage Dependent Calcium Channel ◽  
Voltage Dependent ◽  
Living Organisms ◽  
Insight Into ◽  
Ca2 Channels

Voltage-dependent Ca2+ channels (Cavs) are indispensable for coupling action potentials with Ca2+ signaling in living organisms. The structure of Cavs is similar to that of voltage-dependent Na+ channels (Navs). It is known that prokaryotic Navs can obtain Ca2+ selectivity by negative charge mutations of the selectivity filter, but native prokaryotic Cavs had not yet been identified. We report the first identification of a native prokaryotic Cav, CavMr, whose selectivity filter contains a smaller number of negatively charged residues than that of artificial prokaryotic Cavs. A relative mutant whose selectivity filter was replaced with that of CavMr exhibits high Ca2+ selectivity. Mutational analyses revealed that the glycine residue of the CavMr selectivity filter is a determinant for Ca2+ selectivity. This glycine residue is well conserved among subdomains I and III of eukaryotic Cavs. These findings provide new insight into the Ca2+ selectivity mechanism that is conserved from prokaryotes to eukaryotes.

scholarly journals The mechanism of tubocurarine action on mechanoreceptor channels in the protozoan Stentor coeruleus

1985 ◽  
Vol 117 (1) ◽  
pp. 215-235
Author(s):  
D. C. Wood
Keyword(s):  
Mechanical Stimulation ◽  
Action Potentials ◽  
Response Probability ◽  
Linear Increase ◽  
Membrane Properties ◽  
Reversible Binding ◽  
Exponential Component ◽  
Voltage Dependent ◽  
Stentor Coeruleus ◽  
Highly Correlated

(+)-Tubocurarine (TC) decreases the probability that the protozoan, Stentor coeruleus Ehrenberg, will contract in response to mechanical stimulation, because it selectively depresses mechanoreceptor currents. Resting membrane properties and action potentials are not significantly altered by the drug. Stentor incubated in media containing radioactively labelled TC (TC*) retain TC* after extensive washing despite a rather high apparent KD (19.7 mumol l-1). The incubation curve for TC* binding exhibits an initial exponential rise followed by a linear increase. Wash-out of bound TC* and elimination of the exponential component of the incubation curve is observed if the TC* incubation is followed by a 5-s exposure to 8% urea; therefore, the exponential component represents a reversible binding process. TC* binding in the exponential component is highly correlated (r less than −0.96) with the depression in receptor current and response probability when incubation time, drug concentration and drug (gallamine, TC, decamethonium and succinylcholine) are varied. These correlations suggest that the exponential binding is to functional mechanoreceptors. Mechanoreceptor currents are decreased by hyperpolarization and increased by depolarization, indicating that the mechanoreceptor channel is voltage-dependent. At hyperpolarized potentials the channels are in a form (the U form) which cannot be opened by mechanical stimulation; at depolarized potentials they are in a form (the R form) which can be opened. TC appears to bind to the U form with higher affinity than to the R form, since depolarization reduces the amount of bound TC* and relieves the depression of mechanoreceptor current produced by TC.

Initiation of facial motoneurone migration is dependent on rhombomeres 5 and 6

Development ◽  
2001 ◽  
Vol 128 (19) ◽  
pp. 3707-3716
Author(s):  
Michèle Studer
Keyword(s):  
Chick Embryo ◽  
Environmental Cues ◽  
Motor Nucleus ◽  
Migratory Behaviour ◽  
In Ovo ◽  
Intrinsic Factors ◽  
Extrinsic Cues ◽  
Facial Motor Nucleus ◽  
Migratory Path ◽  
Embryo Chick

In mammals, facial branchiomotor (FBM) neurones are born in ventral rhombomere (r) 4 and migrate through r5 to dorsal r6 where they form the facial motor nucleus. This pattern of migration gives rise to the distinctive appearance of the internal genu of the facial nerve, which is lacking in birds. To distinguish between extrinsic cues and intrinsic factors in the caudal migration of FBM neurones, this study takes advantage of the evolutionary migratory difference between mouse and chick in generating mouse-chick chimaeras in ovo. After the homotopic transplantation of mouse r5 and/or r6 into a chick embryo, chick ventral r4 neurones redirected their cell bodies towards the ectopic mouse source and followed a caudal migratory path, reminiscent of mouse FBM neurones. In a second series of grafting experiments, when mouse r4 was transplanted in place of chick r4, mouse r4 neurones were unable to migrate into chick r5, although mouse and chick cells were able to mix freely within r4. Thus, these data suggest that local environmental cues embedded in mouse r5 and r6 are directly involved in initiating caudal migration of FBM neurones. In addition, they demonstrate that chick FBM neurones are competent to recapitulate a migratory behaviour that has been lost during avian phylogeny.

scholarly journals Foxp3 enhancers synergize to maximize regulatory T cell suppressive capacity

2021 ◽  
Vol 218 (8) ◽  
Author(s):  
Xinying Zong ◽  
Xiaolei Hao ◽  
Beisi Xu ◽  
Jeremy Chase Crawford ◽  
Shaela Wright ◽  
...  
Keyword(s):  
Foxp3 Expression ◽  
Regulatory Elements ◽  
Environmental Cues ◽  
Cell Repertoire ◽  
Intrinsic Factors ◽  
Receptor Repertoire ◽  
Suppressive Capacity ◽  
Extrinsic Cues ◽  
Cell Induction ◽  
Lineage Stability

T reg cells bearing a diverse antigen receptor repertoire suppress pathogenic T cells and maintain immune homeostasis during their long lifespan. How their robust function is determined genetically remains elusive. Here, we investigate the regulatory space of the cis-regulatory elements of T reg lineage–specifying factor Foxp3. Foxp3 enhancers are known as distinct readers of environmental cues controlling T reg cell induction or lineage stability. However, their single deficiencies cause mild, if any, immune dysregulation, leaving the key transcriptional mechanisms determining Foxp3 expression and thereby T reg cell suppressive capacity uncertain. We examined the collective activities of Foxp3 enhancers and found that they coordinate to maximize T reg cell induction, Foxp3 expression level, or lineage stability through distinct modes and that ablation of synergistic enhancers leads to lethal autoimmunity in young mice. Thus, the induction and maintenance of a diverse, stable T reg cell repertoire rely on combinatorial Foxp3 enhancers, suggesting broad, stage-specific, synergistic activities of cell-intrinsic factors and cell-extrinsic cues in determining T reg cell suppressive capacity.

Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

1988 ◽  
Vol 255 (4) ◽  
pp. E469-E474
Author(s):  
J. P. Kile ◽  
M. S. Amoss
Keyword(s):  
Luteinizing Hormone ◽  
Ionophore A23187 ◽  
Channel Blockers ◽  
Hormone Release ◽  
Primary Cells ◽  
Rat Pituitary ◽  
Voltage Dependent ◽  
Lh Release ◽  
Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

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