Type II sodium channels in spinal cord astrocytes in situ: immunocytochemical observations

Sodium Channel Nav1.3 Is Expressed by Polymorphonuclear Neutrophils during Mouse Heart and Kidney Ischemia In Vivo and Regulates Adhesion, Transmigration, and Chemotaxis of Human and Mouse Neutrophils In Vitro

BACKGROUND

Voltage-gated sodium channels generate action potentials in excitable cells, but they have also been attributed noncanonical roles in nonexcitable cells. We hypothesize that voltage-gated sodium channels play a functional role during extravasation of neutrophils.

METHODS

Expression of voltage-gated sodium channels was analyzed by polymerase chain reaction. Distribution of Nav1.3 was determined by immunofluorescence and flow cytometry in mouse models of ischemic heart and kidney injury. Adhesion, transmigration, and chemotaxis of neutrophils to endothelial cells and collagen were investigated with voltage-gated sodium channel inhibitors and lidocaine in vitro. Sodium currents were examined with a whole cell patch clamp.

RESULTS

Mouse and human neutrophils express multiple voltage-gated sodium channels. Only Nav1.3 was detected in neutrophils recruited to ischemic mouse heart (25 ± 7%, n = 14) and kidney (19 ± 2%, n = 6) in vivo. Endothelial adhesion of mouse neutrophils was reduced by tetrodotoxin (56 ± 9%, unselective Nav-inhibitor), ICA121431 (53 ± 10%), and Pterinotoxin-2 (55 ± 9%; preferential inhibitors of Nav1.3, n = 10). Tetrodotoxin (56 ± 19%), ICA121431 (62 ± 22%), and Pterinotoxin-2 (59 ± 22%) reduced transmigration of human neutrophils through endothelial cells, and also prevented chemotactic migration (n = 60, 3 × 20 cells). Lidocaine reduced neutrophil adhesion to 60 ± 9% (n = 10) and transmigration to 54 ± 8% (n = 9). The effect of lidocaine was not increased by ICA121431 or Pterinotoxin-2.

CONCLUSIONS

Nav1.3 is expressed in neutrophils in vivo; regulates attachment, transmigration, and chemotaxis in vitro; and may serve as a relevant target for antiinflammatory effects of lidocaine.

The Role of Voltage-Gated Sodium Channels in Pain Signaling

Acute pain signaling has a key protective role and is highly evolutionarily conserved. Chronic pain, however, is maladaptive, occurring as a consequence of injury and disease, and is associated with sensitization of the somatosensory nervous system. Primary sensory neurons are involved in both of these processes, and the recent advances in understanding sensory transduction and human genetics are the focus of this review. Voltage-gated sodium channels (VGSCs) are important determinants of sensory neuron excitability: they are essential for the initial transduction of sensory stimuli, the electrogenesis of the action potential, and neurotransmitter release from sensory neuron terminals. Nav1.1, Nav1.6, Nav1.7, Nav1.8, and Nav1.9 are all expressed by adult sensory neurons. The biophysical characteristics of these channels, as well as their unique expression patterns within subtypes of sensory neurons, define their functional role in pain signaling. Changes in the expression of VGSCs, as well as posttranslational modifications, contribute to the sensitization of sensory neurons in chronic pain states. Furthermore, gene variants in Nav1.7, Nav1.8, and Nav1.9 have now been linked to human Mendelian pain disorders and more recently to common pain disorders such as small-fiber neuropathy. Chronic pain affects one in five of the general population. Given the poor efficacy of current analgesics, the selective expression of particular VGSCs in sensory neurons makes these attractive targets for drug discovery. The increasing availability of gene sequencing, combined with structural modeling and electrophysiological analysis of gene variants, also provides the opportunity to better target existing therapies in a personalized manner.

A Lifetime's Adventure in Extracellular K+ Regulation: The Scottish Connection

In a career that has spanned 45 years and shows no signs of slowing down, Dr Bruce Ransom has devoted considerable time and energy to studying regulation of interstitial K⁺. When Bruce commenced his studies in 1969 virtually nothing was known of the functions of glial cells, but Bruce’s research contributed to the physiological assignation of function to mammalian astrocytes, namely interstitial K⁺ buffering. The experiments that I describe in this review concern the response of the membrane potential (Em) of in vivo cat cortical astrocytes to changes in [K⁺]_o, an experimental manoeuvre that was achieved in two different ways. The first involved recording the Em of an astrocyte while the initial aCSF was switched to one with different K⁺, whereas in the second series of experiments the cortex was stimulated and the response of the astrocyte Em to the K⁺ released from neighbouring neurons was recorded. The astrocytes responded in a qualitatively predictable manner, but quantitatively the changes were not as predicted by the Nernst equation. Elevations in interstitial K⁺ are not sustained and K⁺ returns to baseline rapidly due to the buffering capacity of astrocytes, a phenomenon studied by Bruce, and his son Chris, published 27 years after Bruce’s initial publications. Thus, a lifetime spent investigating K⁺ buffering has seen enormous advances in glial research, from the time cells were identified as ‘presumed’ glial cells or ‘silent cells’, to the present day, where glial cells are recognised as contributing to every important physiological brain function.

The influence of sodium on pathophysiology of multiple sclerosis

Multiple sclerosis (MS) is a chronic, inflammatory, autoimmune disease of the central nervous system, and is an important cause of disability in young adults. In genetically susceptible individuals, several environmental factors may play a partial role in the pathogenesis of MS. Some studies suggests that high-salt diet (>5 g/day) may contribute to the MS and other autoimmune disease development through the induction of pathogenic Th17 cells and pro-inflammatory cytokines in both humans and mice. However, the precise mechanisms of pro-inflammatory effect of sodium chloride intake are not yet explained. The purpose of this review was to discuss the present state of knowledge on the potential role of environmental and dietary factors, particularly sodium chloride on the development and course of MS.

Regulation of neurovascular coupling in autoimmunity to water and ion channels

Much progress has been made in understanding autoimmune channelopathies, but the underlying pathogenic mechanisms are not always clear due to broad expression of some channel proteins. Recent studies show that autoimmune conditions that interfere with neurovascular coupling in the central nervous system (CNS) can lead to neurodegeneration. Cerebral blood flow that meets neuronal activity and metabolic demand is tightly regulated by local neural activity. This process of reciprocal regulation involves coordinated actions of a number of cell types, including neurons, glia, and vascular cells. In particular, astrocytic endfeet cover more than 90% of brain capillaries to assist blood-brain barrier (BBB) function, and wrap around synapses and nodes of Ranvier to communicate with neuronal activity. In this review, we highlight four types of channel proteins that are expressed in astrocytes, regarding their structures, biophysical properties, expression and distribution patterns, and related diseases including autoimmune disorders. Water channel aquaporin 4 (AQP4) and inwardly rectifying potassium (Kir4.1) channels are concentrated in astrocytic endfeet, whereas some voltage-gated Ca(2+) and two-pore domain K(+) channels are expressed throughout the cell body of reactive astrocytes. More channel proteins are found in astrocytes under normal and abnormal conditions. This research field will contribute to a better understanding of pathogenic mechanisms underlying autoimmune disorders.

Voltage-gated sodium channel Nav 1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+ /Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage-gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB-R7943, at a dose that blocks reverse mode of the Na(+) /Ca(2+) exchanger (NCX), and by knockdown of Nav 1.5 mRNA. We also show that astrocytes display a robust [Ca(2+) ]i transient after mechanical injury and demonstrate that this [Ca(2+) ]i response is also attenuated by TTX, KB-R7943, and Nav 1.5 mRNA knockdown. Our results suggest that Nav 1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca(2+) ]i .

Astrocytes within multiple sclerosis lesions upregulate sodium channel Nav1.5

Astrocytes are prominent participants in the response of the central nervous system to injury, including neuroinflammatory insults. Rodent astrocytes in vitro have been shown to express voltage-gated sodium channels in a dynamic manner, with a switch in expression of tetrodotoxin-sensitive to tetrodotoxin-resistant channels in reactive astrocytes. However, the expression of sodium channels in human astrocytes has not been studied, and it is not known whether there are changes in the expression of sodium channels in reactive astrocytes of the human central nervous system. Here, we demonstrate a focal and robust upregulation of sodium channel Nav1.5 in reactive astrocytes at the borders of, and within, active and chronic multiple sclerosis lesions. Nav1.5 was only detectable at very low levels in astrocytes within multiple sclerosis macroscopically normal-appearing white matter or in normal control brain. Nav1.1, Nav1.2, Nav1.3 and Nav1.6 showed little or no expression in astrocytes within normal control tissue and limited upregulation in active multiple sclerosis lesions. Nav1.5 was also expressed at high levels in astrocytes in tissue surrounding new and old cerebrovascular accidents and brain tumours. These results demonstrate the expression of Nav1.5 in human astrocytes and show that Nav1.5 expression is dynamic in these cells. Our observations suggest that the upregulated expression of Nav1.5 in astrocytes may provide a compensatory mechanism, which supports sodium/potassium pump-dependent ionic homoeostasis in areas of central nervous system injury.

Sodium channel expression within chronic multiple sclerosis plaques

Multiple sclerosis (MS) is characterized by focal destruction of myelin sheaths, gliotic scars, and axonal damage that contributes to the accumulation of nonremitting clinical deficits. Previous studies have demonstrated coexpression of sodium channel Nav1.6 and the sodium-calcium exchanger (NCX), together with beta-amyloid precursor protein (beta-APP), a marker of axonal damage, in degenerating axons within acute MS lesions. Axonal degeneration is less frequent within chronic MS lesions than in acute plaques, although current evidence suggests that axonal loss in chronic lesions ("slow burn") is a major contributor to accumulating disability. It is not known, however, whether axonal degenerations in chronic and acute lesions share common mechanisms, despite radically differing extracellular milieus. In this study, the expression of sodium channels Nav1.2 and Nav1.6 and of NCX was examined in chronic MS plaques within the spinal cord. Nav1.2 immunostaining was not observed along demyelinated axons in chronic lesions but was expressed by scar and reactive astrocytes within the plaque. Nav1.6 immunoreactivity, which was intense at nodes of Ranvier in normal appearing white matter in the same sections, was present in approximately one-third of the demyelinated axons within these plaques in a patchy rather than continuous distribution. NCX was not detected in demyelinated axons within chronic lesions, although it was clearly present within the scar astrocytes surrounding the demyelinated axons. beta-APP accumulation occurred in a small percentage of axons within chronic lesions within the spinal cord, but beta-APP was not preferentially present in axons that expressed Nav1.6. These observations suggest that different mechanisms underlie axonal degeneration in acute and chronic MS lesions, with axonal injury occurring at sites of coexpression of Nav1.6 and NCX in acute lesions but independent of coexpression of these 2 molecules in chronic lesions.

Molecular characterization of voltage-gated sodium channels in human gliomas

Voltage-sensitive sodium channels appear to be an electrophysiological hallmark of gliomas. However, the expression of channel subtypes is unclear in these tumors. In this study different gliomas were investigated for the expression of sodium channel subtypes Na(v)1.1, Na(v)1.2, Na(v)1.3, Na(v)1.4, Na(v)1.6, and Na(x)(Na(v)2.1) using RT-PCR. At least one subtype of channels could be detected in each tumor. High-grade gliomas expressed fewer sodium channel subtypes and these at weaker levels than low-grade tumors. Expression of Na(v)1.6, the most abundant isoform in the CNS, was almost absent in the gliomas except the pilocytic variant. Our study gives clear evidence for a differential expression of sodium channel subtypes in gliomas and indicates a predominant expression of channels related to malignancy grades.

Glial membrane channels and receptors in epilepsy: impact for generation and spread of seizure activity

Epilepsy is a condition in the brain characterized by repetitively occurring seizures. While various changes in neuronal properties have been reported to accompany or induce seizure activity in human or experimental epilepsy, other studies suggested that glial cells might be involved in epileptogenesis. Recent findings demonstrate that in the course of the disease, glial cells not only undergo structural alterations but also display distinct functional properties. Several studies identified reduced inwardly rectifying K(+) currents in astrocytes of epileptic tissue, which probably results in disturbances of the K(+) homeostasis. Other data hinted at an abnormal increase in [Ca(2+)](i) in astrocytes through enhanced activity of glial glutamate receptors. This review summarizes current knowledge of alterations of plasma membrane channels and receptors of macroglial cells in epilepsy and discusses the putative importance of these changes for the generation and spread of seizure activity.

Ion channels in glial cells

Functional and molecular analysis of glial voltage- and ligand-gated ion channels underwent tremendous boost over the last 15 years. The traditional image of the glial cell as a passive, structural element of the nervous system was transformed into the concept of a plastic cell, capable of expressing a large variety of ion channels and neurotransmitter receptors. These molecules might enable glial cells to sense neuronal activity and to integrate it within glial networks, e.g., by means of spreading calcium waves. In this review we shall give a comprehensive summary of the main functional properties of ion channels and ionotropic receptors expressed by macroglial cells, i.e., by astrocytes, oligodendrocytes and Schwann cells. In particular we will discuss in detail glial sodium, potassium and anion channels, as well as glutamate, GABA and ATP activated ionotropic receptors. A majority of available data was obtained from primary cell culture, these results have been compared with corresponding studies that used acute tissue slices or freshly isolated cells. In view of these data, an active glial participation in information processing seems increasingly likely and a physiological role for some of the glial channels and receptors is gradually emerging.

Expression of the mRNA for the beta 2 subunit of the voltage-dependent sodium channel in rat CNS

Expression of the voltage-dependent sodium channel has been analysed in adult rat central nervous system by Northern blotting and in situ hybridization. Northern blots showed that all the territories studied express beta 2 transcripts, albeit with widely varying levels (with cerebellum >> hippocampus > brain > brainstem > spinal cord). In situ hybridization confirmed that in these structures, all the neuronal cell bodies contain beta 2 mRNA; expression was particularly high in the granule cells of the cerebellum, in both pyramidal cell layer and dentate gyrus in the hippocampus, and in spinal cord motor neurons. Northern blots also showed that RNA extracted from optic nerve and cultured cortical astrocytes contained beta 2 mRNA, while it was totally absent from sciatic nerve. In situ hybridization evidenced the presence of a numerous population of beta 2-positive cells in cerebellum white matter, spinal cord white matter, and in corpus callosum, where frontal sections showed labelled cells arranged in the chain-like or row pattern typical of interfascicular oligodendrocytes. Combination of antiglial fibrillary acid protein (GFAP) immunofluorescent histochemistry with detection of beta 2 mRNA evidenced that expression of the transcripts was indeed restricted to GFAP-negative cells in white matter.

Pharmacological characterization of Na+ influx via voltage-gated Na+ channels in spinal cord astrocytes

Spinal cord astrocytes display a high density of voltage-gated Na+ channels. To study the contribution of Na+ influx via these channels to Na+ homeostasis in cultured spinal cord astrocytes, we measured intracellular Na+ concentration ([Na+]i) with the fluorescent dye sodium-binding benzofuran isophthalate. Stellate and nonstellate astrocytes, which display Na+ currents with different properties, were differentiated. Baseline [Na+]i was 8.5 mM in these cells and was not altered by 100 microM tetrodotoxin (TTX). Inhibition of Na+ channel inactivation by veratridine (100 microM) evoked a [Na+]i increase of 47.1 mM in 44% of stellate and 9.7 mM in 64% of nonstellate astrocytes. About 30% of cells reacted to veratridine with a [Na+]i decrease of approximately 2 mM. Qualitatively similar [Na+]i changes were caused by aconitine. The effects of veratridine were blocked by TTX, amplified by (alpha-)scorpion toxin and usually were readily reversible. Veratridine-induced [Na+]i increases were reduced upon membrane depolarization with elevated extracellular [K+]. Recovery to baseline [Na+]i was unaltered during blocking of K+ channels with 4-aminopyridine. [Na+]i increases evoked by the ionotropic non-N-methyl--aspartate receptor agonist kainate were not altered by TTX. Our results indicate that influx of Na+ via voltage- gated Na+ channels is not a prerequisite for glial Na+,K+-ATPase activity in spinal cord astrocytes at rest nor does it seem to be involved in [Na+]i increases evoked by kainate. During pharmacological inhibition of Na+ channel inactivation, however, Na+ channels can serve as prominent pathways of Na+ influx and mediate large perturbations in [Na+]i, suggesting that Na+ channel inactivation plays an important functional role in these cells.

Effects of log P and phenyl ring conformation on the binding of 5-phenylhydantoins to the voltage-dependent sodium channel

Binding to the neuronal voltage-dependent sodium channel (NVSC) was evaluated for 12 5-phenylhydantoins which systematically varied either log P and/or 5-phenyl ring orientation. The linear correlation of log P with in vitro sodium channel binding activity (log IC50) for hydantoins 1-12 and diphenylhydantoin (DPH) (r2 = 0.638) suggested that simple partitioning into the lipid phase is important but not sufficient to account for the effects of hydantoins on the NVSC. Comparisons among different hydantoins with the same log P but different low-energy phenyl ring orientations revealed that, in addition to log P, the correct 5-phenyl orientation is important for efficient binding.

Action potential-like responses in B104 cells with low Na+ channel densities

Action potential generation and Na+ currents were studied in B104 neuroblastoma cells in vitro using the whole-cell patch-clamp method in voltage-clamp and current-clamp mode. Action potential-like responses were elicited in 38 of 42 cells, with a threshold close to -55 mV for depolarizing stimuli, and -56 mV for anode-break stimuli. Response amplitudes were larger when cells were held at more negative prepulse potentials, and were well fit by a Boltzmann distribution with a midpoint of approx. -75 mV, close to the V1/2 for Na+ current steady-state inactivation in these cells. Cells displaying action potential-like responses exhibited a peak Na+ current density of 133 +/- 0.14 pA/pF (range, 10.2-296.2 pA/pF) and a low gK:gNa ratio (0.0067 +/- 0.0023). Exposure to 0.1 mM Cd2+ did not block the generation of action potential-like responses in B104 cells, while 1 microM TTX abolished the responses. We conclude that low densities of Na+ channels (< 3/microns2, and < 1/micron2 in some cells) can support the generation of action potential-like responses in B104 cells if they are held at hyperpolarized levels to remove inactivation. The low leak and K+ conductance of these cells may contribute to their ability to generate action potential-like responses under these circumstances.

Voltage-gated Na+ channels in glia: properties and possible functions

Glial cells are nervous-system cells that have classically been considered to be inexcitable. Despite their lack of electrical excitability, they can express voltage-activated Na+ channels with properties similar to the Na+ channels used by excitable cells to generate action potentials. The functional role that these voltage-activated Na+ channels play in glia is unclear. Three functions have been proposed: (1) glial cells might synthesize Na+ channels and donate them to adjacent neurons, thereby reducing the biosynthetic load of neurons; (2) Na+ channels might endow glial cells with the ability to sense electric activity of neighboring neurons, and might thus play a role in neuro-glial communication; and (3) Na+ influx through voltage-gated Na+ channels could be important to fuel the glial (Na+,K+)-ATPase, thereby facilitating and possibly modulating K+ uptake from the extracellular space.

Expression of mRNA for a sodium channel in subfamily 2 in spinal sensory neurons

RNA blot analysis and non-isotopic in situ hybridization cytochemistry were used to study the expression of the mRNA for the glial sodium channel NaG, belonging to Na+ channel subfamily 2, in rat dorsal root ganglia (DRG). mRNA hybridizing at high stringency with an antisense riboprobe against the NaG sequence was observed in both Schwann cells and spinal sensory neurons in situ within DRG, but was expressed at higher levels in the latter. In contrast, hybridization was not detectable in neurons within hippocampus, cerebellum and spinal cord. The expression of the mRNA hybridizing with the NaG probe appears to be developmentally regulated in both Schwann cells and DRG neurons, with levels increasing as development proceeds. Thus, in addition to the mRNAs for types I and II/IIA alpha-subunits and beta 1-subunit in DRG neurons and types II/IIA and III alpha-subunits beta 1-subunit in Schwann cells, the mRNA for an additional sodium channel belonging to subfamily 2 is expressed in these cells in situ.

Type II brain sodium channel expression in non-neuronal cells: embryonic rat osteoblasts

Although voltage-sensitive sodium channels play a central role in electrogenesis in neurons, rat brain sodium channels are also present in some glial cells. To determine whether rat brain sodium channel alpha-subunit isotypes are expressed in other cell types, we examined osteoblasts within the embryonic day 17 (E17) vertebral column with in situ hybridization and immunocytochemical methods. For in situ hybridization studies, riboprobes hybridizing to isoform-specific sequences in the 3'-noncoding region of sodium channel mRNAs (NCI, NCII and NCIII) were utilized. Sodium channel mRNA I and III were not detectable in osteoblasts of the vertebra centrum or neural arches in E17 rats. In contrast, sodium channel mRNA II was moderately expressed by osteoblasts in the developing vertebral column of E17 rats. In immunocytochemical experiments, antipeptide antibodies directed against conserved and isotype-specific regions of the sodium channel alpha-subunit were used. Antibody SP20, which recognizes a conserved region of the sodium channel, intensely stains osteoblasts in both the vertebra centrum and neural arches. Antibody SP11-I, which recognizes sodium channel I, exhibited negligible-to-low levels of immunostaining in vertebral column osteoblasts. Osteoblasts reacted with antibody SP11-II, which recognizes sodium channel II, displayed moderate levels of immunostaining. Antibody SP32-III, which recognizes sodium channel III, displayed negligible levels of staining in osteoblasts within vertebra centrum and neural arches. These results demonstrate that osteoblasts in situ within E17 vertebral columns express sodium channel II mRNA and protein. Together with previous electrophysiological observations, the present results suggest that functional sodium channels are expressed in osteoblasts in vivo. These results extend the range of non-neuronal cells known to express rat brain sodium channels.

Isoform-specific expression of sodium channels in astrocytes in vitro: immunocytochemical observations

The expression of sodium channel alpha-subunit isoforms in astrocytes cultured from P-0 rat spinal cord and P-7 rat optic nerve was examined utilizing immunocytochemical methods with antibodies generated against conserved and isoform-specific amino acid sequences of the rat brain sodium channel. In spinal cord cultures at 5 days in vitro (DIV), both stellate and flat astrocytes were immunostained with antibody SP20, which recognizes a conserved sequence common to sodium channel types I, II/IIA, and III. Antibody SP11-I, which is directed against a subtype-specific sequence in sodium channel I, did not yield detectable staining in spinal cord astrocytes. Antibody SP11-II, which is directed against a subtype-specific sequence in sodium channel II, immunostained both stellate and flat spinal cord astrocytes, although with less intensity than SP20. Antibody SP32-III, which is directed against a subtype-sequence in sodium channel III, immunostained stellate but not flat spinal cord astrocytes. SP20, SP11-II, and SP32-III staining persisted in stellate spinal cord astrocytes through 14-21 DIV, while SP20 and SP11-II immunostaining in flat spinal cord astrocytes was attenuated with time in culture. In optic nerve cultures at 5 DIV, SP20 staining was present in both stellate and flat astrocytes, but at reduced levels compared to spinal cord astrocytes. With increased time in culture SP20 staining was maintained in stellate optic nerve astrocytes but was gradually lost in flat optic nerve astrocytes. Stellate optic nerve astrocytes exhibited low levels of staining with SP11-I, SP11-II, and SP32-III. Flat optic nerve astrocytes lacked or displayed very low SP11-II staining, and SP11-I and SP32-III staining was not detectable. These observations demonstrate that cultures astrocytes are immunoreactive to antibodies generated against conserved and isotype-specific peptide sequences of rat brain sodium channels, and further suggest that there are different patterns of sodium channel expression between flat vs. stellate astrocytes and in astrocytes derived from different regions of the CNS.

Differential Na+ channel beta 1 subunit mRNA expression in stellate and flat astrocytes cultured from rat cortex and cerebellum: a combined in situ hybridization and immunocytochemistry study

Astrocytes have been shown to express voltage-sensitive Na+ channels, but the molecular structure of these channels is not yet known. Recent studies have demonstrated the expression of rat brain voltage-sensitive Na+ channel mRNAs in astrocytes. In this study, we used a combined non-radioactive in situ hybridization/immunocytochemistry method to investigate the expression of voltage-sensitive Na+ channel beta 1 subunit (Na beta 1) mRNA in definitively identified, GFAP-positive astrocytes cultured from two different regions of the rat brain, cerebrum and cerebellum. In general, two morphologically distinct types of GFAP-positive astrocytes were observed in culture: flat, fibroblast-like and stellate, process-bearing. We observed a differential expression of Na beta 1 mRNA in GFAP-positive astrocytes: 1) stellate astrocytes expressed Na beta 1 mRNA, although the level of Na beta 1 mRNA expression was variable, and 2) flat astrocytes generally did not express Na beta 1 mRNA. Moreover, Bergmann-like cells from cerebellum did not express Na beta 1 mRNA, while the granule cells associated with Bergmann-like cell expressed Na beta 1 mRNA. These observations indicate that Na beta 1 mRNA is differentially expressed in rat astrocytes with various morphologies in vitro.