Bone morphogenetic protein-4 induces upregulation of Cav3.1 Ca2+ channels in HL-1 atrial myocytes

Cardiac T-type Ca²⁺ channels are reexpressed in atrial and ventricular myocytes under various pathological conditions such as post-myocardial infarction, hypertrophy, and heart failure, but relatively little is known about the mechanisms. Our previous study found that bone morphogenetic protein-4 (BMP4) was reexpressed in pathological cardiac hypertrophy models and BMP4-mediated cardiomyocyte hypertrophy. We hypothesized that BMP4 could upregulate cardiac T-type Ca²⁺ channels in HL-1 atrial myocytes. The T-type Ca²⁺ currents were recorded by using the patch-clamp technique, and the expressions of Cav3.1 and Cav3.2 were measured by real-time PCR method in HL-1 cells. BMP4 and Cav3.1 mRNA expressions increased in the left atrium from the pressure overload-induced hypertrophy of mice hearts. BMP4 treatment for 48 h induced increase of Cav3.1 but not Cav3.2 mRNA expression in HL-1 cells, and the increase was inhibited by BMP4 inhibitor noggin. Acute treatment with BMP4 did not affect T-type Ca²⁺ currents, but chronic treatment (48 h) significantly increased the amplitude of T-type Ca²⁺ currents in HL-1 cells. Chronic treatment with BMP4 induced upregulation of NADPH oxidase-4 (NOX4), increase of reactive oxygen species (ROS) level, and activation of mitogen-activated protein kinase (MAPK)-activated protein kinases c-jun N-terminal kinases (JNK) and p38. BMP4-induced upregulation of Cav3.1 mRNA was inhibited by NADPH oxidase inhibitor apocynin, the radical scavenger tempol, JNK inhibitor SP600125, and p38 inhibitor SB203580. In conclusion, BMP4 induces upregulation of Cav3.1 Ca²⁺ channels and T-type Ca²⁺ currents in HL-1 atrial myocytes through ROS/MAPK pathways.     

Expression of recombinant calcium channels support secretion in a mouse pheochromocytoma cell line

We have characterized a recently established mouse pheochromocytoma cell line (MPC 9/3L) as a useful model for studying neurotransmitter release and neuroendocrine secretion. MPC 9/3L cells express many of the proteins involved in Ca2+-dependent neurotransmitter release but do not express functional endogenous Ca2+-influx pathways. When transfected with recombinant N-type Ca2+ channel subunits alpha1B,beta2a,alpha2delta (Cav2.2), the cells expressed robust Ca2+ currents that were blocked by omega-conotoxin GVIA. Activation of N-type Ca2+ currents caused rapid increases in membrane capacitance of the MPC 9/3L cells, indicating that the Ca2+ influx was linked to exocytosis of vesicles similar to that reported in chromaffin or PC12 cells. Synaptic protein interaction (synprint) sites, like those found on N-type Ca2+ channels, are thought to link voltage-dependent Ca2+ channels to SNARE proteins involved in synaptic transmission. Interestingly, MPC 9/3L cells transfected with either LC-type (alpha1C, beta2a, alpha2delta, Cav1.2) or T-type (alpha1G, beta2a, alpha2delta, Cav3.1) Ca2+ channel subunits, which do not express synprint sites, expressed appropriate Ca2+ currents that supported rapid exocytosis. Thus MPC 9/3L cells provide a unique model for the study of exocytosis in cells expressing specific Ca2+ channels of defined subunit composition without complicating contributions from endogenous channels. This model may help to distinguish the roles that different Ca2+ channels play in Ca2+-dependent secretion.     

Cannabinoid CB1 receptor signaling dichotomously modulates inhibitory and excitatory synaptic transmission in rat inner retina

In the inner retina, ganglion cells (RGCs) integrate and process excitatory signal from bipolar cells (BCs) and inhibitory signal from amacrine cells (ACs). Using multiple labeling immunohistochemistry, we first revealed the expression of the cannabinoid CB1 receptor (CB1R) at the terminals of ACs and BCs in rat retina. By patch-clamp techniques, we then showed how the activation of this receptor dichotomously regulated miniature inhibitory postsynaptic currents (mIPSCs), mediated by GABA_A receptors and glycine receptors, and miniature excitatory postsynaptic currents (mEPSCs), mediated by AMPA receptors, of RGCs in rat retinal slices. WIN55212-2 (WIN), a CB1R agonist, reduced the mIPSC frequency due to an inhibition of L-type Ca²⁺ channels no matter whether AMPA receptors were blocked. In contrast, WIN reduced the mEPSC frequency by suppressing T-type Ca²⁺ channels only when inhibitory inputs to RGCs were present, which could be in part due to less T-type Ca²⁺ channels of cone BCs, presynaptic to RGCs, being in an inactivation state under such condition. This unique feature of CB1R-mediated retrograde regulation provides a novel mechanism for modulating excitatory synaptic transmission in the inner retina. Moreover, depolarization of RGCs suppressed mIPSCs of these cells, an effect that was eliminated by the CB1R antagonist SR141716, suggesting that endocannabinoid is indeed released from RGCs.     

T-type channels-secretion coupling: evidence for a fast low-threshold exocytosis

T-type channels are transient low-voltage-activated (LVA) Ca²⁺ channels that control Ca²⁺ entry in excitable cells during small depolarizations around resting potential. Studies in the past 20 years focused on the biophysical, physiological, and molecular characterization of T-type channels in most tissues. This led to a well-defined picture of the functional role of LVA channels in controlling low-threshold spikes, oscillatory cell activity, muscle contraction, hormone release, cell growth and differentiation. So far, little attention has been devoted to the role of T-type channels in transmitter release, which mainly involves channel types belonging to the high-voltage-activated (HVA) Ca²⁺ channel family. However, evidence is accumulating in favor of a unique participation of T-type channels in fast transmitter release. Clear data are now reported in reciprocal synapses of the retina and olfactory bulb, synaptic contacts between primary afferent and second order nociceptive neurons, rhythmic inhibitory interneurons of invertebrates and clonal cell lines transfected with recombinant α₁ channel subunits. T-type channels also regulate the large dense-core vesicle release of neuroendocrine cells where Ca²⁺ dependence, rate of vesicle release, and size of readily releasable pool appear comparable to those associated to HVA channels. This suggests that when sufficiently expressed and properly located near the release zones, T-type channels can trigger fast low-threshold secretion. In this study, we will review the main findings that assign a specific task to T-type channels in fast exocytosis, discussing their possible involvement in the control of the Ca²⁺-dependent processes regulating exocytosis like vesicle depletion and vesicle recycling.     

Voltage-gated Ca<Superscript>2+</Superscript> channel mRNAs and T-type Ca<Superscript>2+</Superscript> currents in rat gonadotropin-releasing hormone neurons

Gonadotropin-releasing hormone (GnRH) neurons play a pivotal role in the neuroendocrine regulation of reproduction. We have previously reported that rat GnRH neurons exhibit voltage-gated Ca²⁺ currents. In this study, oligo-cell RT-PCR was carried out to identify subtypes of the α₁ subunit of voltage-gated Ca²⁺ channels in adult rat GnRH neurons. GnRH neurons expressed mRNAs for all five types of voltage-gated Ca²⁺ channels. For T-type Ca²⁺ channels, α_1H was dominantly expressed in GnRH neurons. Electrophysiological analysis in acute slice preparations revealed that GnRH neurons from adult rats exhibited T-type Ca²⁺ currents with fast inactivation kinetics (~20 ms at −30 mV) and a time constant of recovery from inactivation of ~0.6 s. These results indicate that rat GnRH neurons express subtypes of the α₁ subunit for all five types of voltage-gated Ca²⁺ channel, and that α_1H was the dominant subtype in T-type Ca²⁺ channels.     

Role of T-type channels in vasomotor function: team player or chameleon?

Low-voltage-activated T-type calcium channels play an important role in regulating cellular excitability and are implicated in conditions, such as epilepsy and neuropathic pain. T-type channels, especially Cav3.1 and Cav3.2, are also expressed in the vasculature, although patch clamp studies of isolated vascular smooth muscle cells have in general failed to demonstrate these low-voltage-activated calcium currents. By contrast, the channels which are blocked by T-type channel antagonists are high-voltage activated but distinguishable from their L-type counterparts by their T-type biophysical properties and small negative shifts in activation and inactivation voltages. These changes in T-channel properties may result from vascular-specific expression of splice variants of Cav3 genes, particularly in exon 25/26 of the III–IV linker region. Recent physiological studies suggest that T-type channels make a small contribution to vascular tone at low intraluminal pressures, although the relevance of this contribution is unclear. By contrast, these channels play a larger role in vascular tone of small arterioles, which would be expected to function at lower intra-vascular pressures. Upregulation of T-type channel function following decrease in nitric oxide bioavailability and increase in oxidative stress, which occurs during cardiovascular disease, suggests that a more important role could be played by these channels in pathophysiological situations. The ability of T-type channels to be rapidly recruited to the plasma membrane, coupled with their subtype-specific localisation in signalling microdomains where they could modulate the function of calcium-dependent ion channels and pathways, provides a mechanism for rapid up- and downregulation of vasoconstriction. Future investigation into the molecules which govern these changes may illuminate novel targets for the treatment of conditions such as therapy-resistant hypertension and vasospasm.     

Calcium channels in chromaffin cells: focus on L and T types

Voltage-gated Ca2+ channels (Cav) are highly expressed in the adrenal chromaffin cells of mammalian species. Besides shaping action potential waveforms, they are directly involved in the excitation-secretion coupling underlying catecholamine release and, possibly, control other Ca2+-dependent events that originate near the membrane. These functions are shared by a number of Cav channel types (L, N, P/Q, R and T) which have different structure-function characteristics and whose degree of expression changes remarkably among mammalian species. Understanding precisely the functioning of each voltage-gated Ca2+ channels is a crucial task that helps clarifying the Ca2+-dependent mechanisms controlling exocytosis during physiological and pathological conditions. In this paper, we focus on classical and new roles that L- and T-type channels play in the control of chromaffin cell excitability and neurotransmitter release. Interestingly, L-type channels are shown to be implicated in the spontaneous autorhythmicity of chromaffin cells, while T-type channels, which are absent in adult chromaffin cells, are coupled with secretion and can be recruited following long-term beta-adrenergic stimulation or chronic hypoxia. This suggests that like other cells, adrenal chromaffin cells undergo effective remodelling of membrane ion channels and cell functioning during prolonged stress conditions.     

Expression pattern of voltage-dependent calcium channel subunits in hippocampal inhibitory neurons in mice

Different subtypes of voltage-dependent calcium channels (VDCCs) generate various types of calcium currents that play important role in neurotransmitter release, membrane excitability, calcium transients and gene expression. Well-established differences in the physiological properties and variable sensitivity of hippocampal GABAergic inhibitory neurons to excitotoxic insults suggest that the calcium homeostasis, thus VDCC subunits expression pattern is likely different in subclasses of inhibitory cells. Using double-immunohistochemistry, here we report that in mice: 1) Cav2.1 and Cav3.1 subunits are expressed in almost all inhibitory neurons; 2) subunits responsible for the L-type calcium current (Cav1.2 and Cav1.3) are infrequently co-localized with calretinin inhibitory cell marker while Cav1.3 subunit, at least in part, tends to compensate for the low expression of Cav1.2 subunit in parvalbumin-, metabotropic glutamate receptor 1alpha- and somatostatin-immunopositive inhibitory neurons; 3) Cav2.2 subunit is expressed in the majority of inhibitory neurons except in calbindin-reactive inhibitory cells; 4) Cav2.3 subunit is expressed in the vast majority of the inhibitory cells except in parvalbumin- and calretinin-immunoreactive neurons where the proportion of expression of this subunit is considerably lower. These data indicate that VDCC subunits are differentially expressed in hippocampal GABAergic interneurons, which could explain the diversity in their electrophysiological properties, the existence of synaptic plasticity in certain inhibitory neurons and their vulnerability to stressful stimuli.     

Calcium-dependent inhibition of T-type calcium channels by TRPV1 activation in rat sensory neurons

We studied the inhibitory effects of transient receptor potential vanilloid-1 (TRPV1) activation by capsaicin on low-voltage-activated (LVA, T-type) Ca²⁺ channel and high-voltage-activated (HVA; L, N, P/Q, R) currents in rat DRG sensory neurons, as a potential mechanism underlying capsaicin-induced analgesia. T-type and HVA currents were elicited in whole-cell clamped DRG neurons using ramp commands applied before and after 30-s exposures to 1 μM capsaicin. T-type currents were estimated at the first peak of the I–V characteristics and HVA at the second peak, occurring at more positive potentials. Small and medium-sized DRG neurons responded to capsaicin producing transient inward currents of variable amplitudes, mainly carried by Ca²⁺. In those cells responding to capsaicin with a large Ca²⁺ influx (59% of the total), a marked inhibition of both T-type and HVA Ca²⁺ currents was observed. The percentage of T-type and HVA channel inhibition was prevented by replacing Ca²⁺ with Ba²⁺ during capsaicin application or applying high doses of intracellular BAPTA (20 mM), suggesting that TRPV1-mediated inhibition of T-type and HVA channels is Ca²⁺-dependent and likely confined to membrane nano-microdomains. Our data are consistent with the idea that TRPV1-induced analgesia may derive from indirect inhibition of both T-type and HVA channels which, in turn, would reduce the threshold of nociceptive signals generation (T-type channel inhibition) and nociceptive synaptic transmission (HVA-channels inhibition).     

Models of calcium permeation through T-type channels

Ca²⁺ entry is indispensable part of intracellular Ca²⁺ signaling, which is vital for most of cellular functions. Low voltage-activated (LVA or T-type) calcium channels belong to the family of voltage-gated calcium channels (VGCCs) which provide Ca²⁺ entry in response to membrane depolarization. VGCCs are generally characterized by exceptional Ca²⁺ selectivity combined with high permeation rate, thought to be determined by the presence in their selectivity filter of a versatile Ca²⁺ binding site formed by four glutamate residues (EEEE motif). The subfamily of LVA channels includes three members, Cav3.1, Cav3.2 and Cav3.3. They all possess two aspartates instead of glutamates (i.e., EEDD motif) in their selectivity filter and are the least Ca²⁺-selective of all VGCCs. They also have the lowest conductance, weakly discriminate Ca²⁺, Sr²⁺ and Ba²⁺ and demonstrate channel-specific sensitivity to divalent metal blockers, such as Ni²⁺. The available data suggest that EEDD binding site of LVA channels is more rigid compared to EEEE one, and their selectivity permeation and block are determined by two supplementary low-affinity intrapore Ca²⁺ binding sites located above and below EEDD locus. In addition, LVA channels have extracellular metal binding site that allosterically regulates channel’s gating, permeation and block depending on trace metals concentration.     

CaV3.2 is the major molecular substrate for redox regulation of T-type Ca2+ channels in the rat and mouse thalamus

Although T-type Ca²⁺ channels in the thalamus play a crucial role in determining neuronal excitability and are involved in sensory processing and pathophysiology of epilepsy, little is known about the molecular mechanisms involved in their regulation. Here, we report that reducing agents, including endogenous sulfur-containing amino acid l -cysteine, selectively enhance native T-type currents in reticular thalamic (nRT) neurons and recombinant Ca_V3.2 (α1H) currents, but not native and recombinant Ca_V3.1 (α1G)- and Ca_V3.3 (α1I)-based currents. Consistent with this data, T-type currents of nRT neurons from transgenic mice lacking Ca_V3.2 channel expression were not modulated by reducing agents. In contrast, oxidizing agents inhibited all native and recombinant T-type currents non-selectively. Thus, our findings directly demonstrate that Ca_V3.2 channels are the main molecular substrate for redox regulation of neuronal T-type channels. In addition, because thalamic T-type channels generate low-threshold Ca²⁺ spikes that directly correlate with burst firing in these neurons, differential redox regulation of these channels may have an important function in controlling cellular excitability in physiological and pathological conditions and fine-tuning of the flow of sensory information into the central nervous system.     

The phosphodiesterase III inhibitor olprinone inhibits hippocampal glutamate release via a cGMP/PKG pathway

Olprinone, an inhibitor of cyclic nucleotide phosphodiesterase III, inhibited an increase in intracellular Ca²⁺ concentrations for acutely dissociated rat hippocampal pyramidal neurons induced by extracellular high K⁺ (35 mM) depolarization. Olprinone (100 μM) significantly reduced spontaneous glutamate release from rat hippocampal slices. Furthermore, olprinone significantly decreased the rate of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor-mediated miniature excitatory postsynaptic currents (AMPA-mEPSCs) monitored from CA1 pyramidal neurons of rat hippocampal slices, and the effect was blocked by KT5823, an inhibitor of protein kinase G (PKG), but not by H-89, an inhibitor of protein kinase A (PKA). In the PKA assay using PC-12 cells, olprinone did not activate PKA. Taken together, the results of the present study show that olprinone attenuates intracellular Ca²⁺ rise through voltage-sensitive Ca²⁺ channels and inhibits presynaptic glutamate release via a cGMP/PKG pathway.     

甲状腺素对大鼠心肌T型钙通道蛋白和mRNA的影响

目的:观察甲状腺素对大鼠心肌T型钙通道Cav3.1、Cav3.2和Cav3.3表达的影响,探讨T型钙通道表达变化与甲亢性心脏病引起的心律失常之间的关系。方法:选取健康SD大鼠20只,随机分为正常对照组和甲亢性心脏病组(n=10),腹腔注射L-甲状腺素(0.5 mg/kg)连续35 d建立大鼠甲亢性心脏病模型。检测各组大鼠血清T3和T4的含量,测定各组大鼠心脏指数和心肌细胞横径,并行心电图检查;免疫组化和Western blot检测各组大鼠心肌T型钙通道蛋白的表达;RT-PCR检测心肌T型钙通道mRNA的表达。结果:造模35 d后与正常对照组比较,甲亢性心脏病组大鼠血清T3和T4含量明显升高,心脏指数和心肌细胞横径明显增加(P0.05),并发生心律失常;免疫组化、Western blot和RT-PCR结果显示,甲亢性心脏病组大鼠心肌Cav3.1表达较正常对照组明显增加(P0.05),Cav3.2表达明显减少(P0.01),Cav3.3的表达无变化。结论:甲状腺素可促进心肌Cav3.1mRNA和蛋白的表达,抑制Cav3.2 mRNA和蛋白的表达,而对Cav3.3的表达则没有影响。Cav3.1和Cav3.2的表达变化可能与甲亢性心脏病心律失常的发生有关。     

Properties and role of voltage-dependent calcium channels during mouse skeletal muscle differentiation

Skeletal muscle differentiation depends on calcium ions, but it is yet unclear whether calcium entry through voltage-dependent calcium channels (VDCCs) contributes to the myoblast fusion process. In this study, we investigate whether calcium influx through functional T-type VDCCs precedes and affects mouse satellite cell fusion. We report here on the properties and the role of the VDCCs expressed in differentiating mouse muscular cells using both the C2C12 cell line and primary cultures of satellite cells. We present electrophysiological and biochemical evidence demonstrating that T-type and L-type VDCCs are not present in C2C12 and primary cultures of mouse satellite cells prior to the fusion stage. Although mRNA for the T-type Ca_V3.2 subunit was detected in differentiated C2C12 cells, no T-type calcium currents could be recorded, while both T-type and L-type calcium currents were detected after the fusion process in primary cultures. In addition, chronic application of 30 μM nickel, known to inhibit T-type Ca_V3.2 channels, did not alter the fusion of C2C12 cells and mouse satellite cells in primary culture. Overall, the data indicate that, unlike in humans, Ca_V3.2 T-type calcium channels play no role in mouse satellite cell fusion.     

神经降压素对大鼠脊髓背角胶状质内突触前神经递质释放的影响

目的:研究内源性神经肽神经降压素(neurotensin,NT)在脊髓背角胶状质(substantia gelatinosa,SG)内对突触前神经递质释放的影响。方法:采用全细胞电压膜片钳记录方法,在脊髓薄片上观察NT对SG内微小兴奋性突触后电流(mEPSCs)和微小抑制性突触后电流(mIPSCs)的频率和幅值的影响。结果:(1)灌流NT(2μmol/L)对SG内神经元mEPSCs的频率和幅值均无明显影响,说明NT不影响SG内兴奋性神经递质的释放;(2)灌流NT(2μmol/L)能增加SG内神经元mIPSCs的频率,但对幅值无明显影响,即NT可引起突触前抑制性神经递质的释放增加,但对突触后神经元无明显影响。结论:NT可通过增加SG内抑制性神经递质释放的途径抑制伤害性信息的传递,从而实现镇痛效应。     

Short- and long-term roles of phosphatidylinositol 4,5-bisphosphate PIP2 on Cav3.1- and Cav3.2-T-type calcium channel current

T-type calcium (Ca²⁺) channels play important physiological functions in excitable cells including cardiomyocyte. Phosphatidylinositol-4,5-bisphosphate (PIP₂) has recently been reported to modulate various ion channels’ function. However the actions of PIP₂ on the T-type Ca²⁺ channel remain unclear. To elucidate possible effects of PIP₂ on the T-type Ca²⁺ channel, we applied patch clamp method to investigate recombinant Ca_V3.1- and Ca_V3.2-T-type Ca²⁺ channels expressed in mammalian cell lines with PIP₂ in acute- and long-term potentiation. Short- and long-term potentiation of PIP₂ shifted the activation and the steady-state inactivation curve toward the hyperpolarization direction of Ca_V3.1-I_Ca.T without affecting the maximum inward current density. Short- and long-term potentiation of PIP₂ also shifted the activation curve toward the hyperpolarization direction of Ca_V3.2-I_Ca.T without affecting the maximum inward current density. Conversely, long-term but not short-term potentiation of PIP₂ shifted the steady-state inactivation curve toward the hyperpolarization direction of Ca_V3.2-I_Ca.T. Long-term but not short-term potentiation of PIP₂ blunted the voltage-dependency of current decay Ca_V3.1-I_Ca.T. PIP₂ modulates Ca_V3.1- and Ca_V3.2-I_Ca.T not by their current density but by their channel gating properties possibly through its membrane-delimited actions.     

Regulation of T-type calcium channels by Rho-associated kinase

We investigated the regulation of T-type channels by Rho-associated kinase (ROCK). Activation of ROCK via the endogenous ligand lysophosphatidic acid (LPA) reversibly inhibited the peak current amplitudes of rat Ca(v)3.1 and Ca(v)3.3 channels without affecting the voltage dependence of activation or inactivation, whereas Ca(v)3.2 currents showed depolarizing shifts in these parameters. LPA-induced inhibition of Ca(v)3.1 was dependent on intracellular GTP, and was antagonized by treatment with ROCK and RhoA inhibitors, LPA receptor antagonists or GDPssS. Site-directed mutagenesis of the Ca(v)3.1 alpha1 subunit revealed that the ROCK-mediated effects involve two distinct phosphorylation consensus sites in the domain II-III linker. ROCK activation by LPA reduced native T-type currents in Y79 retinoblastoma and in lateral habenular neurons, and upregulated native Ca(v)3.2 current in dorsal root ganglion neurons. Our data suggest that ROCK is an important regulator of T-type calcium channels, with potentially far-reaching implications for multiple cell functions modulated by LPA.     

Novel vistas of calcium-mediated signalling in the thalamus

Traditionally, the role of calcium ions (Ca²⁺) in thalamic neurons has been viewed as that of electrical charge carriers. Recent experimental findings in thalamic cells have only begun to unravel a highly complex Ca²⁺ signalling network that exploits extra- and intracellular Ca²⁺ sources. In thalamocortical relay neurons, interactions between T-type Ca²⁺ channel activation, Ca²⁺-dependent regulation of adenylyl cyclase activity and the hyperpolarization-activated cation current (I_h) regulate oscillatory burst firing during periods of sleep and generalized epilepsy, while a functional triad between Ca²⁺ influx through high-voltage-activated (most likely L-type) Ca²⁺ channels, Ca²⁺-induced Ca²⁺ release via ryanodine receptors (RyRs) and a repolarizing mechanism (possibly via K⁺ channels of the BK_Ca type) supports tonic spike firing as required during wakefulness. The mechanisms seem to be located mostly at dendritic and somatic sites, respectively. One functional compartment involving local GABAergic interneurons in certain thalamic relay nuclei is the glomerulus, in which the dendritic release of GABA is regulated by Ca²⁺ influx via canonical transient receptor potential channels (TRPC), thereby presumably enabling transmitters of extrathalamic input systems that are coupled to phospholipase C (PLC)-activating receptors to control feed-forward inhibition in the thalamus. Functional interplay between T-type Ca²⁺ channels in dendrites and the A-type K⁺ current controls burst firing, contributing to the range of oscillatory activity observed in these interneurons. GABAergic neurons in the reticular thalamic (RT) nucleus recruit a specific set of Ca²⁺-dependent mechanisms for the generation of rhythmic burst firing, of which a particular T-type Ca²⁺ channel in the dendritic membrane, the Ca²⁺-dependent activation of non-specific cation channels (I_CAN) and of K⁺ channels (SK_Ca type) are key players. Glial Ca²⁺ signalling in the thalamus appears to be a basic mechanism of the dynamic and integrated exchange of information between glial cells and neurons. The conclusion from these observations is that a localized calcium signalling network exists in all neuronal and probably also glial cell types in the thalamus and that this network is dedicated to the precise regulation of the functional mode of the thalamus during various behavioural states.