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Hee-Sup Shin

Publications and source records attributed to Hee-Sup Shin.

At least 37 records · Page 2Linked to original sources
PubMed2004

P/Q-type Ca2+ channel alpha1A regulates synaptic competition on developing cerebellar Purkinje cells.

Synapse formation depends critically on the competition among inputs of multiple sources to individual neurons. Cerebellar Purkinje cells have highly organized synaptic wiring from two distinct sources of excitatory afferents. Single climbing fibers innervate proximal dendrites of Purkinje cells, whereas numerous parallel fibers converge on their distal dendrites. Here, we demonstrate that the P/Q-type Ca2+ channel alpha1A, a major Ca2+ channel subtype in Purkinje cells, is crucial for this organized synapse formation. In the alpha1A knock-out mouse, many ectopic spines were protruded from proximal dendrites and somata of Purkinje cells. Innervation territory of parallel fibers was expanded proximally to innervate the ectopic spines, whereas that of climbing fibers was regressed to the basal portion of proximal dendrites and somata. Furthermore, multiple climbing fibers consisting of a strong climbing fiber and one or a few weaker climbing fibers, persisted in the majority of Purkinje cells and were cowired to the same somata, proximal dendrites, or both. Therefore, the lack of alpha1A results in the persistence of parallel fibers and surplus climbing fibers, which should normally be expelled from the compartment innervated by the main climbing fiber. These results suggest that a P/Q-type Ca2+ channel alpha1A fuels heterosynaptic competition between climbing fibers and parallel fibers and also fuels homosynaptic competition among multiple climbing fibers. This molecular function facilitates the distal extension of climbing fiber innervation along the dendritic tree of the Purkinje cell and also establishes climbing fiber monoinnervation of individual Purkinje cells.

Animals↗
PubMed2004

Biophysical and pharmacological characterization of spermatogenic T-type calcium current in mice lacking the CaV3.1 (alpha1G) calcium channel: CaV3.2 (alpha1H) is the main functional calcium channel in wild-type spermatogenic cells.

Mammalian acrosome reaction (AR) requires successive activation of three different types of calcium channels (T-type channels, Inositol-3-phosphate (InsP3) receptors, and TRPC2 channels). All the calcium signaling is under the control of the activation of the first-one, a T-type calcium channel. The molecular characterization of the T-type calcium channel is still a matter of debate, previous reports showing the presence of transcripts for Ca(V)3.1 and Ca(V)3.2 subunits. Using mice deficient for Ca(V)3.1 subunit, we show that the T-type current density in spermatogenic cells is not reduced in deficient mice versus control mice. We characterized the biophysical and pharmacological properties of T-type current in spermatogenic cells from Ca(V)3.1 deficient mice. Biophysical and pharmacological properties of spermatogenic T-type current from wild-type and Ca(V)3.1 deficient mice demonstrate that Ca(V)3.3 does not contribute to T-type current. Moreover, nickel and amiloride inhibit T-type currents in deficient and wild-type mice with similar potencies. These results demonstrate that T-type currents in spermatogenic cells is due to Ca(V)3.2 subunit and that Ca(V)3.1 contributes to a very negligible extent to the T-type currents. Thus, the deficient Ca(V)3.1 mouse model allows the characterization of native Ca(V)3.2 currents in spermatogenic cells. Spermatogenic Ca(V)3.2 currents present specific feature in comparison to the cloned Ca(V)3.2 current so far. More particularly, the time-dependence of recovery from short-term inactivation of native spermatogenic Ca(V)3.2 is close to 100 millisecond, a value expected for Ca(V)3.1 current.

Amiloride↗
PubMed2004

Null mutation of alpha1D Ca2+ channel gene results in deafness but no vestibular defect in mice.

Multiple Ca2+ channels confer diverse functions to hair cells of the auditory and vestibular organs in the mammalian inner ear. We used gene-targeting technology to generate alpha1D Ca2+ channel-deficient mice to determine the physiological role of these Ca2+ channels in hearing and balance. Analyses of auditory-evoked brainstem recordings confirmed that alpha1D-/- mice were deaf and revealed that heterozygous (alpha1D+/-) mice have increased hearing thresholds. However, hearing deficits in alpha1D+/- mice were manifested mainly by the increase in threshold of low-frequency sounds. In contrast to impaired hearing, alpha1D-/- mice have balance performances equivalent to their wild-type littermates. Light and electron microscope analyses of the inner ear revealed outer hair cell loss at the apical cochlea, but no apparent abnormality at the basal cochlea and the vestibule. We determined the mechanisms underlying the auditory function defects and the normal vestibular functions by examining the Ba2+ currents in cochlear inner and outer hair cells versus utricular hair cells in alpha1D+/- mice. Whereas the whole-cell Ba2+ currents in inner hair cells consist mainly of the nimodipine-sensitive current (approximately 85%), the utricular hair cells express only approximately 50% of this channel subtype. Thus, differential expression of alpha1D channels in the cochlear and utricular hair cells confers the phenotype of the alpha1D null mutant mice. Because vestibular and cochlear hair cells share common features and null deletion of several genes have yielded both deafness and imbalance in mice, alpha1D null mutant mice may serve as a model to disentangle vestibular from auditory-specific functions.

Animals↗
PubMed2004

Altered GABAergic neurotransmission in mice lacking dopamine D2 receptors.

The levels of glutamic acid decarboxylase (GAD) were strongly increased in the cortex and the striatum in dopamine D2 receptors null (D2R-/-) mice, which show a significant locomotor impairment. In this study, the effects of different GABAergic drugs on locomotor activity were analyzed in D2R-/- mice. After administering muscimol (1 mg/kg), a GABA(A) receptor agonist, the D2R-/- mice showed increased locomotor activity up to 200%. When the muscimol dose was increased (4-6 mg/kg), the D2R-/- mice exhibited seizure-like behavior, and the electroencephalographic (EEG) recordings during these behaviors showed a high amplitude rhythmic epileptiform activity in these mice. In situ hybridization showed that after injecting muscimol in the D2R-/- mice, the expression of enkephalin and immediate early gene, NGFI-A, was closely regulated with the locomotor activity regulated by GABAergic stimulation. These results suggest that the absence of D2R alters the GABAergic neurotransmission, specifically on GABA(A)-receptor mediated signaling, and stimulating the GABA(A) receptor can reverse the dysfunction of GABAergic inhibition in the motor circuits in the basal ganglia.

Animals↗
PubMed2003

Repression of phospho-JNK and infarct volume in ischemic brain of JIP1-deficient mice.

Mice lacking JIP1, a scaffold protein that organizes JNK pathway components, were constructed independently by two groups. The proposed in vivo function, however, remains contradictory; One study reported that targeted disruption of the jip1 caused embryonic death due to the requirement of JIP1 for fertilized eggs (Thompson et al. [2001] J. Biol. Chem. 276:27745-27748). In contrast, another group (Whitmarsh et al. [2001] Genes Dev. 15:2421-2432) demonstrated that JIP1-deficient mice were viable and that the JIP1 null mutation inhibited the kainic acid-induced JNK activation and neuronal death. The current study was undertaken to re-elucidate the in vivo roles of JIP1 using newly generated JIP1 knockout mice. Our JIP1-deficient mice were viable and healthy. The transient focal ischemic insult produced by middle cerebral artery occlusion (MCAO) strongly activated JNK in brain of jip1(+/+), jip1(+/-), and jip1(-/-) mice. Increased JNK activity was sustained for more than 22 hr in jip1(+/+) and jip1(+/-), whereas it was repressed rapidly in jip1(-/-). Concomitantly, the infarct volume produced by the ischemic insult in jip1(-/-) was reduced notably compared to that in jip1(+/+) brain. These results suggest that JIP1 plays a pivotal role in regulating the maintenance of phosphorylated JNK and neuronal survival in postischemic brain, but is not essential for JNK activation and early development.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Thalamic control of visceral nociception mediated by T-type Ca2+ channels.

Sensations from viscera, like fullness, easily become painful if the stimulus persists. Mice lacking alpha1G T-type Ca2+ channels show hyperalgesia to visceral pain. Thalamic infusion of a T-type blocker induced similar hyperalgesia in wild-type mice. In response to visceral pain, the ventroposterolateral thalamic neurons evokeda surge of single spikes, which then slowly decayed as T type-dependent burst spikes gradually increased. In alpha1G-deficient neurons, the single-spike response persisted without burst spikes. These results indicate that T-type Ca2+ channels underlie an antinociceptive mechanism operating in the thalamus andsupport the idea that burst firing plays a critical role in sensory gating in the thalamus.

Abdominal Pain↗
PubMed2003

Enhanced learning and memory in mice lacking Na+/Ca2+ exchanger 2.

The plasma membrane Na(+)/Ca(2+) exchanger (NCX) plays a role in regulation of intracellular Ca(2+) concentration via the forward mode (Ca(2+) efflux) or the reverse mode (Ca(2+) influx). To define the physiological function of the exchanger in vivo, we generated mice deficient for NCX2, the major isoform in the brain. Mutant hippocampal neurons exhibited a significantly delayed clearance of elevated Ca(2+) following depolarization. The frequency threshold for LTP and LTD in the hippocampal CA1 region was shifted to a lowered frequency in the mutant mice, thereby favoring LTP. Behaviorally, the mutant mice exhibited enhanced performance in several hippocampus-dependent learning and memory tasks. These results demonstrate that NCX2 can be a temporal regulator of Ca(2+) homeostasis and as such is essential for the control of synaptic plasticity and cognition.

Animals↗
PubMed2003

Partial rescue of the Na+-Ca2+ exchanger (NCX1) knock-out mouse by transgenic expression of NCX1.

The null mutation of cardiac Na(+)-Ca(2+) exchanger (NCX1) gene in mice caused death of embryo in utero at embryonic day (ED) 9.0-9.5 and this embryonic lethality appears resulted from abnormal heart development. In the present study, we investigated whether transgenic re-expression of NCX1 in mutant cardiac myocytes could rescue these lethal defects. Transgenic mice expressing the canine NCX1 in a cardiac specific manner were bred into the NCX1 knock-out background but did not prevent the fetal lethality associated with the NCX1 null allele. However, the NCX1 knock-out embryos with an NCX1 transgene survived with heart beatings until ED 10.5 which was one day longer than the survival of the NCX1 knock-out embryos (ED 9.5). At ED 10.5, however, the partially rescued NCX1 embryos might have succumbed to the lack of an organized vasculature in the yolk sacs. The placental labyrinth layer was reduced in size and largely avascular. The transgenic re-expression of NCX1 rescued heart beatings and survived longer, but was still insufficient for the mice to be completely rescued. Importantly, NCX1 was observed to express in the yolk sac and the placenta of wild type mice. The results suggest that defects in extra-embryonic compartments are causal to the lethality, and that NCX1 may play an important role in establishing vascularization in extra-embryonic tissues.

Animals↗
PubMed2003

Altered properties of quantal neurotransmitter release at endplates of mice lacking P/Q-type Ca2+ channels.

Transmission at the mouse neuromuscular junction normally relies on P/Q-type channels, but became jointly dependent on both N- and R-type Ca(2+) channels when the PQ-type channel alpha(1A) subunit was deleted. R-type channels lay close to Ca(2+) sensors for exocytosis and I(K(Ca)) channel activation, like the P/Q-type channels they replaced. In contrast, N-type channels were less well localized, but abundant enough to influence secretion strongly, particularly when action potentials were prolonged. Our data suggested that active zone structures may select among multiple Ca(2+) channels in the hierarchy P/Q >R >N. The alpha(1A)-/- neuromuscular junction displayed several other differences from wild-type: lowered quantal content but greater ability to withstand reductions in the Ca(2+)/Mg(2+) ratio, and little or no paired-pulse facilitation, the latter findings possibly reflecting compensatory mechanisms at individual release sites. Changes in presynaptic function were also associated with a significant reduction in the size of postsynaptic acetylcholine receptor clusters.

4-Aminopyridine↗
PubMed2003

Peroxiredoxin II is essential for sustaining life span of erythrocytes in mice.

Peroxiredoxins (Prxs) are a family of antioxidant proteins that reduce peroxide levels by using reducing agents such as thioredoxin. These proteins were characterized to have a number of cellular functions, including cell proliferation and differentiation and protection of specific proteins from oxidative damage. However, the physiological roles of the peroxiredoxins have not been determined. To clarify the physiological relevance of this protein type, we generated a mouse model deficient in Prx II, which is abundantly expressed in all types of cells. The Prx II-/- mice were healthy in appearance and fertile. However, they had splenomegaly caused by the congestion of red pulp with hemosiderin accumulation. Heinz bodies were detected in their peripheral blood, and morphologically abnormal cells were elevated in the dense red blood cell (RBC) fractions, which contained markedly higher levels of reactive oxygen species (ROS). The Prx II-/- mice had significantly decreased hematocrit levels, but increased reticulocyte counts and erythropoietin levels, indicative of a compensatory action to maintain hematologic homeostasis in the mice. In addition, a labeling experiment with the thiol-modifying reagent biotinylated iodoacetamide (BIAM) in Prx II-/- mice revealed that a variety of RBC proteins were highly oxidized. Our results suggest that Prx II-/- mice have hemolytic anemia and that Prx II plays a major role in protecting RBCs from oxidative stress in mice.

Anemia, Hemolytic↗
PubMed2002

Molecular characterization of a two-domain form of the neuronal voltage-gated P/Q-type calcium channel alpha(1)2.1 subunit.

We characterized the neuronal two-domain (95kD-alpha(1)2.1) form of the alpha(1)2.1 subunit of the voltage-gated calcium channels using genetic and molecular analysis. The 95kD-alpha(1)2.1 is absent in neuronal preparations from CACNA1A null mouse demonstrating that alpha(1)2.1 and 95kD-alpha(1)2.1 arise from the same gene. A recombinant two-domain form (alpha(1AI-II)) of alpha(1)2.1 associates with the beta subunit and is trafficked to the plasma membrane. Translocation of the alpha(1AI-II) to the plasma membrane requires association with the beta subunit, since a mutation in the alpha(1AI-II) that inhibits beta subunit association reduces membrane trafficking. Though the alpha(1AI-II) protein does not conduct any voltage-gated currents, we have previously shown that it generates a high density of non-linear charge movements [Ahern et al., Proc. Natl. Acad. Sci. USA 98 (2001) 6935-6940]. In this study, we demonstrate that co-expression of the alpha(1AI-II) significantly reduces the current amplitude of alpha(1)2.1/beta(1a)/alpha(2)delta channels, via competition for the beta subunit. Taken together, our results demonstrate a dual functional role for the alpha(1AI-II) protein, both as a voltage sensor and modulator of P/Q-type currents in recombinant systems. These studies suggest an in vivo role for the 95kD-alpha(1)2.1 in altering synaptic activity via protein-protein interactions and/or regulation of P/Q-type currents.

Animals↗
PubMed2002

Cerebellar slice cultures from mice lacking the P/Q calcium channel: electroresponsiveness of Purkinje cells.

To investigate the role of P/Q type Ca(2+) channels in determining the firing pattern of Purkinje cells (PCs) we compared the somatically evoked discharge of action potentials (APs) in PCs from 3 to 4 week old cerebellar slice cultures obtained with ataxic mice lacking alpha(1A)-subunit (alpha(-/-)) and with normal mice (non-ataxic alpha(+/-) or alpha(+/+)) using the whole-cell configuration of the patch-clamp recording method. Whereas evoked responses of PCs in normal mice were mainly fast APs, those of PCs from ataxic mice were mainly low-threshold Ca(2+) spikes (LTS). Furthermore, a sustained plateau potential due to the activation of cadmium sensitive Ca(2+) conductances was not observed in PCs from ataxic mice by blocking K(+) channels. These results confirm that P/Q Ca(2+) channels elicit Ca(2+)-dependent plateau potentials and control the propagation of the dendritic LTS to the soma.

Action Potentials↗
PubMed2002

Impaired D2 dopamine receptor function in mice lacking type 5 adenylyl cyclase.

Dopamine receptor subtypes D1 and D2, and many other seven-transmembrane receptors including adenosine receptor A2A, are colocalized in striatum of brain. These receptors stimulate or inhibit adenylyl cyclases (ACs) to produce distinct physiological and pharmacological responses and interact with each other synergistically or antagonistically at various levels. The identity of the AC isoform that is coupled to each of these receptors, however, remains unknown. To investigate the in vivo role of the type 5 adenylyl cyclase (AC5), which is preferentially expressed in striatum, mice deficient for the AC5 gene were generated. The genetic ablation of the AC5 gene eliminated >80% of forskolin-induced AC activity and 85-90% of AC activity stimulated by either D1 or A2A receptor agonists in striatum. However, D1- or A2A-specific pharmaco-behaviors were basically preserved, whereas the signal cascade from D2 to AC was completely abolished in AC5(-/-), and motor activity of AC5(-/-) was not suppressed by treatment of cataleptic doses of the antipsychotic drugs haloperidol and sulpiride. Interestingly, both haloperidol and clozapine at low doses remarkably increased the locomotion of AC5(-/-) in the open field test that was produced in part by a common mechanism that involved the increased activation of D1 dopamine receptors. Together, these results suggest that AC5 is the principal AC integrating signals from multiple receptors including D1, D2, and A2A in striatum and the cascade involving AC5 among diverse D2 signaling pathways is essential for neuroleptic effects of antipsychotic drugs.

Adenylyl Cyclases↗
PubMed2002

Acetylcholine-induced phosphatidylinositol 4,5-bisphosphate depletion does not cause short-term desensitization of G protein-gated inwardly rectifying K+ current in mouse atrial myocytes.

Depletion of phosphatidylinositol 4,5-bisphosphate (PIP(2)) induced by phenylephrine or endothelin causes the inhibition of acetylcholine-activated K(+) current (I(KACh)) in atrial myocytes. In the present study, we have investigated the hypothesis that muscarinic receptor induced PIP(2) depletion also causes inhibition of I(KACh), resulting in desensitization. We confirmed the expression of G(q)-coupled muscarinic receptors in mouse atrial myocytes using reverse transcriptase-polymerase chain reaction. The involvement of M(1) and M(3) receptors in desensitization is examined using specific antagonists, 4-DAMP and pirenzepine, but they significantly reduced peak I(KACh), implying nonspecific M(2) blockade. When ACh-induced phosphoinositide depletion was specifically inhibited using PLCbeta1 knock-out mice, the extent of desensitization during 4 min was 47.5 +/- 3.2%, which was not different from that in wild type (46.8 +/- 2.1%). Phenylephrine-induced phosphoinositide hydrolysis and phenylephrine-induced inhibition of I(KACh) were not affected by PLCbeta1 knock-out. To facilitate PIP(2) depletion, replenishment of PIP(2) was blocked by wortmannin. Wortmannin did not affect the desensitization and the recovery from desensitization. These results suggest that PIP(2) depletion by acetylcholine does not contribute to short-term desensitization of I(KACh). The differential regulation of I(KACh) by different phospholipase C-linked receptors may imply that receptor co-localization is required for PIP(2) to act as a signaling molecule.

Acetylcholine↗
PubMed2002

Functional Roles of Ca(v)1.3 (alpha(1D)) calcium channel in sinoatrial nodes: insight gained using gene-targeted null mutant mice.

We directly examined the role of the Ca(v)1.3 (alpha(1D)) Ca(2+) channel in the sinoatrial (SA) node by using Ca(v)1.3 Ca(2+) channel-deficient mice. A previous report has shown that the null mutant (Ca(v)1.3(-/-)) mice have sinus bradycardia with a prolonged PR interval. In the present study, we show that spontaneous action potentials recorded from the SA nodes show a significant decrease in the beating frequency and rate of diastolic depolarization in Ca(v)1.3(-/-) mice compared with their heterozygous (Ca(v)1.3(+/-)) or wild-type (WT, Ca(v)1.3(+/+)) littermates, suggesting that the deficit is intrinsic to the SA node. Whole-cell L-type Ca(2+) currents (I(Ca,L)s) recorded in single isolated SA node cells from Ca(v)1.3(-/-) mice show a significant depolarization shift in the activation threshold. The voltage-dependent activation of Ca(v)1.2 (alpha(1C)) versus Ca(v)1.3 Ca(2+) channel subunits was directly compared by using a heterologous expression system without beta coexpression. Similar to the I(Ca,L) recorded in the SA node of Ca(v)1.3(-/-) mutant mice, the Ca(v)1.2 Ca(2+) channel shows a depolarization shift in the voltage-dependent activation compared with that in the Ca(v)1.3 Ca(2+) channel. In summary, using gene-targeted deletion of the Ca(v)1.3 Ca(2+) channel, we were able to establish a role for Ca(v)1.3 Ca(2+) channels in the generation of the spontaneous action potential in SA node cells.

Animals↗
PubMed2002

Molecular basis of R-type calcium channels in central amygdala neurons of the mouse.

R-type Ca2+ channels play a critical role in coupling excitability to dendritic Ca2+ influx and neuronal secretion. Unlike other types of voltage-sensitive Ca2+ channels (L, N, P/Q, and T type), the molecular basis for the R-type Ca2+ channel is still unclear, thereby limiting further detailed analyses of R-type Ca2+ channel physiology. The prevailing hypothesis is that alpha(1E) (Ca(V)2.3) gene encodes for R-type Ca2+ channels, but the dearth of critical evidence has rendered this hypothesis controversial. Here we generated alpha1E-deficient mice (alpha1E-/-) and examined the status of voltage-sensitive Ca2+ currents in central amygdala (CeA) neurons that exhibit abundant alpha1E expression and R-type Ca2+ currents. The majority of R-type currents in CeA neurons were eliminated in alpha1E-/- mice whereas other Ca2+ channel types were unaffected. These data clearly indicate that the expression of alpha1E gene underlies R-type Ca2+ channels in CeA neurons. Furthermore, the alpha1E-/- sign mice exhibited signs of enhanced fear as evidenced by their vigorous escaping behavior and aversion to open-field conditions. These latter findings imply a possible role of alpha1E-based R-type Ca2+ currents in amygdala physiology associated with fear.

Amygdala↗
PubMed2002

A perforated patch-clamp study of calcium currents and exocytosis in chromaffin cells of wild-type and alpha(1A) knockout mice.

Simultaneous recordings of inward whole-cell Ca(2+) channel currents (I(Ca) ) and increments of capacitance as an indication of exocytosis (Delta(Cm)), were performed in voltage-clamped single adrenal chromaffin cells from wild-type and alpha(1A) subunit deficient mice, using the perforated-patch configuration of the patch-clamp technique. Using protocol #1 (one single Ca(2+) channel blocker per cell), to dissect the components of I(Ca), L channels contributed 43%, N channels 35% and P/Q channels 30% to the total I(Ca) of wild-type cells. Using protocol #2 (cumulative sequential addition of 3 microm nifedipine, 1 microm omega-conotoxin GVIA, and 1 microm omega-agatoxin IVA), L, N and P/Q channels contributed 40%, 34% and 14%, respectively, to I(Ca); an R component of around 11% remained. In wild-type mice the changes of Delta(Cm) paralleled those of I(Ca). In alpha(1A) deficient mice the L component of I(Ca) rose to 53% while the P/Q disappeared; the N and R components were similar. In these mice, Delta(Cm) associated to N and R channels did not vary; however, the P/Q component was abolished while the L component increased by 20%. In conclusion, exocytosis was proportional to the relative density of each Ca(2+) channel subtype, L, N, P/Q, R. Ablation of the alpha(1A) gene led to a loss of P/Q channel current and to a compensatory increase of L channel-associated secretion; however, this compensation was not sufficient to maintain the overall exocytotic response, that was diminished by 35% in alpha(1A) -deficient mice. This may be due to altered Ca(2+) homeostasis in these mice, as compared to wild mouse chromaffin cells.

Animals↗