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Hee-Sup Shin

Publications and source records attributed to Hee-Sup Shin.

At least 19 recordsLinked to original sources
PubMed2006

Molecular coupling of a Ca2+-activated K+ channel to L-type Ca2+ channels via alpha-actinin2.

Cytoskeletal proteins are known to sculpt the structural architecture of cells. However, their role as bridges linking the functional crosstalk of different ion channels is unknown. Here, we demonstrate that a small conductance Ca(2+)-activated K(+) channels (SK2 channel), present in a variety of cells, where they integrate changes in intracellular Ca(2+) concentration [Ca(2+)(i)] with changes in K(+) conductance and membrane potential, associate with L-type Ca(2+) channels; Ca(v)1.3 and Ca(v)1.2 through a physical bridge, alpha-actinin2 in cardiac myocytes. SK2 channels do not physically interact with L-type Ca(2+) channels, instead, the 2 channels colocalize via their interaction with alpha-actinin2 cytoskeletal protein. The association of SK2 channel with alpha-actinin2 localizes the channel to the entry of external Ca(2+) source, which regulate the channel function. Furthermore, we demonstrated that the functions of SK2 channels in atrial myocytes are critically dependent on the normal expression of Ca(v)1.3 Ca(2+) channels. Null deletion of Ca(v)1.3 channel results in abnormal function of SK2 channel and prolongation of repolarization and atrial arrhythmias. Our study provides insight into the molecular mechanisms of the coupling of SK2 channel with voltage-gated Ca(2+) channel, and represents the first report linking the coupling of 2 different types of ion channels via cytoskeletal proteins.

Actinin↗
PubMed2006

Reduced nicotinic receptor function in sympathetic ganglia is responsible for the hypothermia in the acetylcholinesterase knockout mouse.

Cholinergic signalling in the sympathetic ganglia (SG) contributes to non-shivering thermogenesis by relaying the activation signal from the brain to SG neurons which activate many peripheral tissues to produce heat. Paradoxically, acetylcholinesterase (AChE) inhibitors, which should enhance cholinergic signalling, induce hypothermia. To understand the mechanism of how cholinergic signalling in the SG controls thermoregulation, we analysed infant AChE knockout mice, which are known to show hypothermia by postnatal day 15. Nicotinic receptor currents were reduced in acutely dissociated SG neurons of the AChE-deficient mice by over 40% compared with wild-type mice. When wild-type neurons were treated for 1 h with either oxotremorine-M, a muscarinic agonist, or nicotine, the amplitude of nicotinic receptor currents was also decreased by 40%. The hypothermia in AChE mutant mice was fully rescued by a peripheral injection of both ivermectin, which increases nicotinic receptor currents, and methyl-atropine, a muscarinic antagonist. Our results demonstrate that the hypothermia induced by the lack of AChE activity is primarily caused by a downregulation of nicotinic receptors via prolonged stimulation of muscarinic and nicotinic receptors in SG neurons. The stationary noise analysis of the nicotinic receptor current traces showed that the properties of single-channel activities were not different between the two genotypes, suggesting that the primary reason for downregulation of nicotinic receptors is due to a reduction of the receptors on the surface.

Acetylcholinesterase↗
PubMed2006

Thyrotropin-releasing hormone increases GABA release in rat hippocampus.

Thyrotropin-releasing hormone (TRH) is a tripeptide that is widely distributed in the brain including the hippocampus where TRH receptors are also expressed. TRH has anti-epileptic effects and regulates arousal, sleep, cognition, locomotion and mood. However, the cellular mechanisms underlying such effects remain to be determined. We examined the effects of TRH on GABAergic transmission in the hippocampus and found that TRH increased the frequency of GABAA receptor-mediated spontaneous IPSCs in each region of the hippocampus but had no effects on miniature IPSCs or evoked IPSCs. TRH increased the action potential firing frequency recorded from GABAergic interneurons in CA1 stratum radiatum and induced membrane depolarization suggesting that TRH increases the excitability of interneurons to facilitate GABA release. TRH-induced inward current had a reversal potential close to the K+ reversal potential suggesting that TRH inhibits resting K+ channels. The involved K+ channels were sensitive to Ba2+ but resistant to other classical K+ channel blockers, suggesting that TRH inhibits the two-pore domain K+ channels. Because the effects of TRH were mediated via Galphaq/11, but were independent of its known downstream effectors, a direct coupling may exist between Galphaq/11 and K+ channels. Inhibition of the function of dynamin slowed the desensitization of TRH responses. TRH inhibited seizure activity induced by Mg2+ deprivation, but not that generated by picrotoxin, suggesting that TRH-mediated increase in GABA release contributes to its anti-epileptic effects. Our results demonstrate a novel mechanism to explain some of the hippocampal actions of TRH.

Action Potentials↗
PubMed2006

T-type Ca2+ channels and absence epilepsy.

Burst firing of the thalamic neurons is driven by the low threshold Ca2+ spike generated by Ca2+ influx through T-type Ca2+ channels when these channels are activated by membrane hyperpolarization due to inhibitory inputs. The major inhibitory inputs to the thalamocortical (TC) neurons are from the GABAergic neurons in the thalamic reticular nucleus. Thalamic burst firings have long been implicated in the pathogenesis of absence epilepsy. The recent progress in genetic approaches has provided with an opportunity to examine this issue at the level of an organism. In this review I describe results primarily obtained from the analysis of the mice deficient for the alpha1G locus which is the predominant gene underlying the low threshold Ca2+ currents in the TC neurons. Current results so far demonstrate the essential role of the thalamocortical bursts in certain forms of absence seizures. Understanding of the pathophysiological mechanisms of absence epilepsy may help develop drugs to control the disease.

Animals↗
PubMed2006

Bradycardia and slowing of the atrioventricular conduction in mice lacking CaV3.1/alpha1G T-type calcium channels.

The generation of the mammalian heartbeat is a complex and vital function requiring multiple and coordinated ionic channel activities. The functional role of low-voltage activated (LVA) T-type calcium channels in the pacemaker activity of the sinoatrial node (SAN) is, to date, unresolved. Here we show that disruption of the gene coding for CaV3.1/alpha1G T-type calcium channels (cacna1g) abolishes T-type calcium current (I(Ca,T)) in isolated cells from the SAN and the atrioventricular node without affecting the L-type Ca2+ current (I(Ca,L)). By using telemetric electrocardiograms on unrestrained mice and intracardiac recordings, we find that cacna1g inactivation causes bradycardia and delays atrioventricular conduction without affecting the excitability of the right atrium. Consistently, no I(Ca,T) was detected in right atrium myocytes in both wild-type and CaV3.1(-/-) mice. Furthermore, inactivation of cacna1g significantly slowed the intrinsic in vivo heart rate, prolonged the SAN recovery time, and slowed pacemaker activity of individual SAN cells through a reduction of the slope of the diastolic depolarization. Our results demonstrate that CaV3.1/T-type Ca2+ channels contribute to SAN pacemaker activity and atrioventricular conduction.

Animals↗
PubMed2006

Genetic studies on the role of T-type Ca2+ channels in sleep and absence epilepsy.

Thalamocortical neurons in mammals fire action potentials in two different modes, burst or tonic, depending on the cellular state. The burst firing is driven by the low threshold Ca2+ spike that is generated by Ca2+ influx through T-type Ca2+ channels, and has long been implicated in the pathogenesis of absence epilepsy and the regulation of sleep rhythms. The recent availability of the knock-out mice for the alpha1G locus, encoding the predominant form of T-type channels in thalamocortical neurons, has provided an opportunity to examine those ideas at the level of organism. In this review we will describe recent results demonstrating the essential role of thalamic bursts in certain forms of absence seizures and in some of the sleep rhythms. Available information so far reveals the sensory gating role of thalamic bursts, and thus of alpha1G T-type channels. Understanding of the molecular targets involved in pathophysiological mechanisms will help develop drugs to control those pathological states.

Animals↗
PubMed2005

Multiple receptors coupled to phospholipase C gate long-term depression in visual cortex.

Long-term depression (LTD) in sensory cortices depends on the activation of NMDA receptors. Here, we report that in visual cortical slices, the induction of LTD (but not long-term potentiation) also requires the activation of receptors coupled to the phospholipase C (PLC) pathway. Using immunolesions in combination with agonists and antagonists, we selectively manipulated the activation of alpha1 adrenergic, M1 muscarinic, and mGluR5 glutamatergic receptors. Inactivation of these PLC-coupled receptors prevents the induction of LTD, but only when the three receptors were inactivated together. LTD is fully restored by activating any one of them or by supplying intracellular D-myo-inositol-1,4,5-triphosphate (IP3). LTD was also impaired by intracellular application of PLC or IP3 receptor blockers, and it was absent in mice lacking PLCbeta1, the predominant PLC isoform in the forebrain. We propose that visual cortical LTD requires a minimum of PLC activity that can be supplied independently by at least three neurotransmitter systems. This essential requirement places PLC-linked receptors in a unique position to control the induction of LTD and provides a mechanism for gating visual cortical plasticity via extra-retinal inputs in the intact organism.

Animals↗
PubMed2005

Genetic dissection of theta rhythm heterogeneity in mice.

Rhythmic oscillatory activities at the theta frequency (4-12 Hz) in the hippocampus have long-attracted attention because they have been implicated in diverse brain functions, including spatial cognition. Although studies based on pharmacology and lesion experiments suggested heterogeneity of these rhythms and their behavioral correlates, controversies are abundant on these issues. Here we show that mice harboring a phospholipase C (PLC)-beta1(-/-) mutation (PLC-beta1(-/-) mice) lack one subset of theta rhythms normally observed during urethane anesthesia, alert immobility, and passive whole-body rotation. In contrast, the other subset of theta rhythms observed during walking or running was intact in these mutant mice. PLC-beta1(-/-) mice also have somewhat disrupted theta activity during paradoxical sleep but do have an atropine-resistant component of theta rhythm. In addition, carbachol-induced oscillations were obliterated in hippocampal slices of PLC-beta1(-/-) mice. Interestingly, PLC-beta1(-/-) mice showed deficits in a hidden platform version of the Morris water maze yet performed well in motor coordination tests and a visual platform version of the Morris water maze. The results genetically define the existence of at least two subtypes of theta rhythms and reveal their association with different behaviors.

Analysis of Variance↗
PubMed2005

Functional roles of Cav1.3(alpha1D) calcium channels in atria: insights gained from gene-targeted null mutant mice.

BACKGROUND: Previous data suggest that L-type Ca2+ channels containing the Cav1.3(alpha(1D)) subunit are expressed mainly in neurons and neuroendocrine cells, whereas those containing the Cav1.2(alpha1C) subunit are found in the brain, vascular smooth muscle, and cardiac tissue. However, our previous report as well as others have shown that Cav1.3 Ca2+ channel-deficient mice (Cav1.3(-/-)) demonstrate sinus bradycardia with a prolonged PR interval. In the present study, we extended our study to examine the role of the Cav1.3(alpha1D) Ca2+ channel in the atria of Cav1.3(-/-) mice. METHODS AND RESULTS: We obtained new evidence to demonstrate that there is significant expression of Cav1.3 Ca2+ channels predominantly in the atria compared with ventricular tissues. Whole-cell L-type Ca2+ currents (I(Ca,L)) recorded from single, isolated atrial myocytes from Cav1.3(-/-) mice showed a significant depolarizing shift in voltage-dependent activation. In contrast, there were no significant differences in the I(Ca,L) recorded from ventricular myocytes from wild-type and null mutant mice. We previously documented the hyperpolarizing shift in the voltage-dependent activation of Cav1.3 compared with Cav1.2 Ca2+ channel subunits in a heterologous expression system. The lack of Cav1.3 Ca2+ channels in null mutant mice would result in a depolarizing shift in the voltage-dependent activation of I(Ca,L) in atrial myocytes. In addition, the Cav1.3-null mutant mice showed evidence of atrial arrhythmias, with inducible atrial flutter and fibrillation. We further confirmed the isoform-specific differential expression of Cav1.3 versus Cav1.2 by in situ hybridization and immunofluorescence confocal microscopy. CONCLUSIONS: Using gene-targeted deletion of the Cav1.3 Ca2+ channel, we established the differential distribution of Cav1.3 Ca2+ channels in atrial myocytes compared with ventricles. Our data represent the first report demonstrating important functional roles for Cav1.3 Ca2+ channel in atrial tissues.

Animals↗
PubMed2005

Presynaptic N-type and P/Q-type Ca2+ channels mediating synaptic transmission at the calyx of Held of mice.

At the nerve terminal, both N- and P/Q-type Ca2+ channels mediate synaptic transmission, with their relative contribution varying between synapses and with postnatal age. To clarify functional significance of different presynaptic Ca2+ channel subtypes, we recorded N-type and P/Q-type Ca2+ currents directly from calyces of Held nerve terminals in alpha1A-subunit-deficient mice and wild-type (WT) mice, respectively. The most prominent feature of P/Q-type Ca2+ currents was activity-dependent facilitation, which was absent for N-type Ca2+ currents. EPSCs mediated by P/Q-type Ca2+ currents showed less depression during high-frequency stimulation compared with those mediated by N-type Ca2+ currents. In addition, the maximal inhibition by the GABAB receptor agonist baclofen was greater for EPSCs mediated by N-type channels than for those mediated by P/Q-type channels. These results suggest that the developmental switch of presynaptic Ca2+ channels from N- to P/Q-type may serve to increase synaptic efficacy at high frequencies of activity, securing high-fidelity synaptic transmission.

Animals↗
PubMed2005

Phospholipase C-beta3 mediates the thrombin-induced Ca2+ response in glial cells.

Phospholipase C-beta (PLC-beta) hydrolyses phosphatidylinositol 4,5-bisphosphate and generates inositol 1,4,5-trisphosphate in response to activation of various G protein-coupled receptors (GPCRs). Using glial cells from knock-out mice lacking either PLC-beta1 [PLC-beta1 (-/-)] or PLC-beta3 [PLC-beta3 (-/-)], we examined which isotype of PLC-beta participated in the cellular signaling events triggered by thrombin. Generation of inositol phosphates (IPs) was enhanced by thrombin in PLC-beta1 (-/-) cells, but was negligible in PLC-beta3 (-/-) cells. Expression of PLC-beta3 in PLC-beta3 (-/-) cells resulted in an increase in pertussis toxin (PTx)-sensitive IPs in response to thrombin as well as to PAR1-specific peptide, while expression of PLC-beta1 in PLC-beta1 (-/-) cells did not have any effect on IP generation. The thrombin-induced [Ca2+]i increase was delayed and attenuated in PLC-beta3 (-/-) cells, but normal in PLC-beta1 (-/-) cells. Pertussis toxin evoked a delayed [Ca2+]i increase in PLC-beta3 (-/-) cells as well as in PLC-beta1 (-/-) cells. These results suggest that activation of PLC-beta3 by pertussis toxin-sensitive G proteins is responsible for the transient [Ca2+]i increase in response to thrombin, whereas the delayed [Ca2+]i increase may be due to activation of some other PLC, such as PLC-beta4, acting via PTx-insensitive G proteins.

Animals↗
PubMed2005

Phospholipase Cbeta serves as a coincidence detector through its Ca2+ dependency for triggering retrograde endocannabinoid signal.

Endocannabinoids mediate retrograde signal and modulate transmission efficacy at various central synapses. Although endocannabinoid release is induced by either depolarization or activation of G(q/11)-coupled receptors, it is markedly enhanced by the coincidence of depolarization and receptor activation. Here we report that this coincidence is detected by phospholipase Cbeta1 (PLCbeta1) in hippocampal neurons. By measuring cannabinoid-sensitive synaptic currents, we found that the receptor-driven endocannabinoid release was dependent on physiological levels of intracellular Ca(2+) concentration ([Ca(2+)](i)), and markedly enhanced by depolarization-induced [Ca(2+)](i) elevation. Furthermore, we measured PLC activity in intact neurons by using exogenous TRPC6 channel as a biosensor for the PLC product diacylglycerol and found that the receptor-driven PLC activation exhibited similar [Ca(2+)](i) dependence to that of endocannabinoid release. Neither endocannabinoid release nor PLC activation was induced by receptor activation in PLCbeta1 knockout mice. We therefore conclude that PLCbeta1 serves as a coincidence detector through its Ca(2+) dependency for endocannabinoid release in hippocampal neurons.

Animals↗
PubMed2005

The axon guidance defect of the telencephalic commissures of the JSAP1-deficient brain was partially rescued by the transgenic expression of JIP1.

The JNK interacting protein, JSAP1, has been identified as a scaffold protein for mitogen-activated protein kinase (MAPK) signaling pathways and as a linker protein for the cargo transport along the axons. To investigate the physiological function of JSAP1 in vivo, we generated mice lacking JSAP1. The JSAP1 null mutation produced various developmental deficits in the brain, including an axon guidance defect of the corpus callosum, in which phospho-FAK and phospho-JNK were distributed at reduced levels. The axon guidance defect of the corpus callosum in the jsap1-/- brain was correlated with the misplacement of glial sling cells, which reverted to their normal position after the transgenic expression of JNK interacting protein 1(JIP1). The transgenic JIP1 partially rescued the axon guidance defect of the corpus callosum and the anterior commissure of the jsap1-/- brain. The JSAP1 null mutation impaired the normal distribution of the Ca+2 regulating protein, calretinin, but not the synaptic vesicle marker, SNAP-25, along the axons of the thalamocortical tract. These results suggest that JSAP1 is required for the axon guidance of the telencephalic commissures and the distribution of cellular protein(s) along axons in vivo, and that the signaling network organized commonly by JIP1 and JSAP1 regulates the axon guidance in the developing brain.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Lack of delta waves and sleep disturbances during non-rapid eye movement sleep in mice lacking alpha1G-subunit of T-type calcium channels.

T-type calcium channels have been implicated as a pacemaker for brain rhythms during sleep but their contribution to behavioral states of sleep has been relatively uncertain. Here, we found that mice lacking alpha1(G) T-type Ca(2+) channels showed a loss of the thalamic delta (1-4 Hz) waves and a reduction of sleep spindles (7-14 Hz), whereas slow (<1 Hz) rhythms were relatively intact, when compared with the wild-type during urethane anesthesia and non-rapid eye movement (NREM) sleep. Analysis of sleep disturbances, as defined by the occurrence of brief awakening (BA) episodes during NREM sleep, revealed that mutant mice exhibited a higher incidence of BAs of >16 sec compared with the wild-type, whereas no difference was seen in BAs of <16 sec between the two genotypes. These results are consistent with the previous idea of the distinct nature of delta oscillations and sleep spindles from cortically generated slow waves. These results also suggest that the alpha1(G)-subunit of T-type calcium channels plays a critical role in the genesis of thalamocortical oscillations and contributes to the modulation of sleep states and the transition between NREM sleep and wake states.

Animals↗
PubMed2004

Deletion of N-type calcium channels alters ethanol reward and reduces ethanol consumption in mice.

N-type calcium channels are modulated by acute and chronic ethanol exposure in vitro at concentrations known to affect humans, but it is not known whether N-type channels are important for behavioral responses to ethanol in vivo. Here, we show that in mice lacking functional N-type calcium channels, voluntary ethanol consumption is reduced and place preference is developed only at a low dose of ethanol. The hypnotic effects of ethanol are also substantially diminished, whereas ethanol-induced ataxia is mildly increased. These results demonstrate that N-type calcium channels modulate acute responses to ethanol and are important mediators of ethanol reward and preference.

Alcohol Drinking↗
PubMed2004

Human neural stem cell transplantation reduces spontaneous recurrent seizures following pilocarpine-induced status epilepticus in adult rats.

Transplantation of neural stem cells (NSCs) can replace lost neurons and improve the functional deficits. Cell transplantation strategies have been tried in the epileptic disorder, but the effect of exogenous NSCs is unknown. In this study, we attempted to test the anti-epileptogenic effect of NSCs in adult rats with status epilepticus. Experimental status epilepticus was induced by lithium-pilocarpine injection, and beta galactosidase-encoded human NSCs were transplanted intravenously on the next day of status epilepticus. Spontaneous recurrent seizures were monitored with Racine's seizure severity scale. Immunohistochemistry with anti-beta gal, Tuj-1, NeuN, GFAP, CNPase, GluR2, parvalbumin, and GABA were performed and extracellular field excitatory postsynaptic potentials (fEPSP) were recorded. Human NSCs suppressed spontaneous recurrent seizure formation and transplanted NSCs were differentiated into GABA-immunoreactive interneurons in the damaged hippocampus. Amplitude of fEPSP in the hippocampal CA1 was reduced, which was reversed by picrotoxin. These findings suggest that NSCs could be differentiated into inhibitory interneurons and decrease neuronal excitability, which could prevent spontaneous recurrent seizure formation in adult rats with pilocarpine-induced status epilepticus.

Aggression↗
PubMed2004

Role of the alpha1G T-type calcium channel in spontaneous absence seizures in mutant mice.

Alterations in thalamic T-type Ca2+ channels are thought to contribute to the pathogenesis of absence seizures. Here, we found that mice with a null mutation for the pore-forming alpha1A subunits of P/Q-type channels (alpha1A-/- mice) were prone to absence seizures characterized by typical spike-and-wave discharges (SWDs) and behavioral arrests. Isolated thalamocortical relay (TC) neurons from these mice showed increased T-type Ca2+ currents in vitro. To examine the role of increased T-currents in alpha1A-/- TC neurons, we cross-bred alpha1A-/- mice with mice harboring a null mutation for the gene encoding alpha1G, a major isotype of T-type Ca2+ channels in TC neurons. alpha1A-/-/alpha1G-/- mice showed a complete loss of T-type Ca2+ currents in TC neurons and displayed no SWDs. Interestingly, alpha1A-/-/alpha1G+/- mice had 75% of the T-type Ca2+ currents in TC neurons observed in alpha1A+/+/alpha1G+/+ mice and showed SWD activity that was quantitatively similar to that in alpha1A-/-/alpha1G+/+ mice. Similar results were obtained using double-mutant mice harboring the alpha1G mutation plus another mutation also used as a model for absence seizures, i.e., lethargic (beta4(lh/lh)), tottering (alpha1A(tg/tg)), or stargazer (gamma2(stg/stg)). The present results reveal that alpha1G T-type Ca2+ channels play a critical role in the genesis of spontaneous absence seizures resulting from hypofunctioning P/Q-type channels, but that the augmentation of thalamic T-type Ca2+ currents is not an essential step in the genesis of absence seizures.

Animals↗