Developmental changes in the membrane current pattern, K+ buffer capacity, and morphology of glial cells in the corpus callosum slice

Recent studies indicated that glial cells in tissue culture can express a variety of different voltage-gated channels, while little is known about the presence of such channels in glial cells in vivo. We used a mouse corpus callosum slice preparation, in which after postnatal day 5 (P5) more than 99% of all perikarya belong to glial cells (Sturrock, 1976), to study the current patterns of glial cells during their development in situ. We combined the patch-clamp technique with intracellular labeling using Lucifer yellow (LY) and subsequent ultrastructural characterization. In slices of mice from P6 to P8, we predominantly found cells expressing delayed-rectifier K+ currents. They were similar to those described for cultured glial precursor cells (Sontheimer et al., 1989). A-type K+ currents or Na+ currents were not or only rarely observed, in contrast to cultured glial precursors. LY labeling revealed that numerous thin processes extended radially from the perikaryon of these cells, and ultrastructural observations suggested that they resemble immature glial cells. In slices of older mice (P10-13), when myelination of the corpus callosum has already commenced, many cells were characterized by an almost linear current-voltage relationship. This current pattern was similar to cultured oligodendrocytes (Sontheimer et al., 1989). Most processes of LY-filled cells with such a current profile extended parallel to each other. Electron microscopy showed that these processes surround thick, unmyelinated axons. We suggest that cells with oligodendrocyte-type electrophysiology are promyelinating oligodendrocytes. In contrast to cultured oligodendrocytes, membrane currents of promyelinating oligodendrocytes in the slice decayed during the voltage command. This decay was due not to inactivation, but to a marked change in the potassium equilibrium potential within the voltage jump. This implies that, in the more mature corpus callosum, small membrane polarizations in a physiological range can lead to extensive changes in the K+ gradient across the glial membrane within a few milliseconds.     

Kir potassium channel subunit expression in retinal glial cells: implications for spatial potassium buffering

To understand the role of different K(+) channel subtypes in glial cell-mediated spatial buffering of extracellular K(+), immunohistochemical localization of inwardly rectifying K(+) channel subunits (Kir2.1, Kir2.2, Kir2.3, Kir4.1, and Kir5.1) was performed in the retina of the mouse. Stainings were found for the weakly inward-rectifying K(+) channel subunit Kir4.1 and for the strongly inward-rectifying K(+) channel subunit Kir2.1. The most prominent labeling of the Kir4.1 protein was found in the endfoot membranes of Müller glial cells facing the vitreous body and surrounding retinal blood vessels. Discrete punctate label was observed throughout all retinal layers and at the outer limiting membrane. By contrast, Kir2.1 immunoreactivity was located predominantly in the membrane domains of Müller cells that contact retinal neurons, i.e., along the two stem processes, over the soma, and in the side branches extending into the synaptic layers. The results suggest a model in which the glial cell-mediated transport of extracellular K(+) away from excited neurons is mediated by the cooperation of different Kir channel subtypes. Weakly rectifying Kir channels (Kir4.1) are expressed predominantly in membrane domains where K(+) currents leave the glial cells and enter extracellular "sinks," whereas K(+) influxes from neuronal "sources" into glial cells are mediated mainly by strongly rectifying Kir channels (Kir 2.1). The expression of strongly rectifying Kir channels along the "cables" for spatial buffering currents may prevent an unwarranted outward leak of K(+), and, thus, avoid disturbances of neuronal information processing.     

The effect of brachium conjunctivum transection on a conditioned limb response in the cat

Seven cats were trained to perform a forelimb conditioned response to a paired tone conditioned stimulus (CS)/shock unconditioned stimulus (UCS). Brachium conjunctivum section ipsilateral to the trained limb was carried out following criterion conditioned response (CR) performance. Lesion sites were identified histologically and further confirmed by observation of cellular changes in the dentate and interpositus nuclei ipsilateral to the section. The brachium conjunctivum was found to have been sectioned in four of the seven subjects. Each of these animals demonstrated a total or near-total loss of the CR. Extended postoperative training resulted in no increase in CR performance levels. The unconditioned response (UCR) remained unaffected, as did limb placing, accuracy of striking at moving objects, grooming, running and walking. The results are discussed in the context of an earlier report by McCormick et al. [Bull Psychonom Soc 1981;18:103-5], in which section of the superior cerebellar peduncle was found to abolish a conditioned nictitating membrane response in the rabbit. Taken together, they support the contention of Lavond [Annu Rev Psychol 1993;44:317-42], Thompson [In: Sprague JM, Epstein AN, editors. Progress in Psychobiology and Physiological Psychology. New York: Academic Press 1983, pp. 167-96], Yeo et al. [Behav Brain Res 1984;13:261-66; Exp Brain Res 1985;60:87-98; Exp Brain Res 1985;60:99-113; Exp Brain Res 1992;88:623-38.] and others that the cerebellum represents a critical site for acquisition and retention of a conditioned memory trace.     

Biologically active sequence (KDI) mediates the neurite outgrowth function of the gamma-1 chain of laminin-1.

A neurite outgrowth domain of the gamma1-chain of laminin-1 (RDIAEIIKDI) promotes axon guidance of rat hippocampal neurons, regulates the nuclear movement phase of neuronal migration, and binds to the cellular prion protein (Liesi et al. [1995] J. Neurosci. Res. 134:447-486; Matsuzawa et al. [1998] J. Neurosci. Res. 53:114-124; Graner et al. [2000] Brain Res. Mol. Brain Res. 76:85-92). Using electrophysiology and neuronal culture experiments, we show that this 10 amino acid peptide or its smaller domains induces potassium currents in primary central neurons. Both these currents and the neurotoxicity of high concentrations of the 10 amino acid peptide antigen are prevented by pertussis toxin. The smallest peptide domain capable of inducing both potassium currents and promoting neurite outgrowth of human spinal cord neurons is a tri-peptide KDI. Our results indicate that KDI may be the biologically active domain of the gamma1 laminin, capable of modulating electrical activity and survival of central neurons via a G-protein coupled mechanism. These results expand the wide variety of functions already reported for the members of the laminin-gene family. They suggest that biologically active peptide domains of the gamma1 laminin may provide tools to promote neuronal regeneration after injuries and to enhance neuronal survival during aging and neuronal degeneration.     

Directed spatial potassium redistribution in rat neocortex

The functional role of the glial network as a draining system for extracellular potassium (spatial buffer) was investigated in rat neocortical brain slices. After electrical stimulation, extracellular space volume decreased in the middle cortical layers and increased in the upper cortical layers, confirming predictions for a spatial buffer. The widening of extracellular space was associated with an increase in extracellular potassium. The data suggested a delayed redistribution of potassium from middle to superficial cortical layers. Interruption of gap junctions abolished the widening of extracellular space. The data show that a multicellular directed network connected by gap junctions participates in maintaining potassium homeostasis in brain.     

Is there capacity for anatomical and functional repair in the adult somatosensory thalamus?

The capacity for structural and functional remodeling in damaged adult CNS sensory systems can be studied by replacement of neurons in damaged structures by fetal cells from these anatomical origins. For integration to take place, the replacement paradigm assumes that (a) reconnection of adult host afferent fibers onto developing neurons is possible and (b) that the correct molecular signals exist also in the adult brain for fetal neurons to extend axons and pattern synaptic contacts. We have tried to answer some of these fundamental questions by using neuronal depletion models followed by neuronal replacement in the adult rat CNS (Isacson et al. 1984. Nature (London) 311: 458-460; Isacson et al. 1988. Prog. Brain Res. 78: 13-27; Nothias et al. 1988. Brain Res. 461: 349-354; Peschanski and Isacson. 1988. J. Comp. Neurol. 274: 449-463; Sofroniew et al. 1990. Prog. Brain Res. 82: 313-320). In one such model, kainic acid infusions deplete the ventrobasal complex (VB) of all neurons projecting to the somatosensory cortex, while afferent axons from the lemniscal and monoaminergic systems remain in the area. Direct implantation of fetal neurons (gestation age 15-16) of ventrobasal destination allows reconnection of circuitry to take place at the thalamic level, as studied by anatomical tracers, electron microscopy, and functional 2-deoxyglucose studies, while fetal thalamic VB neurons appear less likely to grow through the internal capsule toward the cortical level.     

Model of potassium dynamics in the central nervous system

A one-dimensional numerical model of potassium dynamics in the central nervous system is developed. The model incorporates the following physiological processes in computing spatial and temporal changes in extracellular K+ concentration, [K+]o: 1) the release of K+ from K+ sources into extracellular space, 2) diffusion of K+ through extracellular space, 3) active uptake of K+ into cells and blood vessels, 4) passive uptake of K+ into a cellular distribution space, and 5) the transfer of K+ by K+ spatial buffer current flow in glial cells. The following tissue parameters can be specified along the single spatial dimension of the model: 1) the volume fraction and tortuosity of extracellular and glial cell spaces, 2) the volume fraction of the cellular distribution space, 3) rate constants of active uptake and passive uptake processes, and 4) glial cell membrane conductance. The model computes variations in [K+]o and current flow through glial cells for three tissue geometries: 1) planar geometry (the retina and the surface of the brain), 2) cylindrical geometry (tissue surrounding a blood vessel), and 3) spherical geometry (tissue surrounding a point source of K+). For simple sources of K+, the performance of the model matches that predicted from analytical equations. Simulations of previous ion dynamics experiments indicate that the model can accurately predict ion diffusion and K+ current flow in the brain. Simulations of electroretinogram generation and K+ siphoning onto blood vessels suggest that unanticipated K+ dynamics mechanisms may be operating in the central nervous system.     

Effects of Acute and Chronic Phenytoin on the Electrolyte Content and the Activities of Na+, K+-, Ca2+, Mg2+ -, and HCO3--ATPases and Carbonic Anhydrase of Neonatal and Adult Rat Cerebral Cortex

Various parameters of anion and cation transport were measured in the cerebral cortex of neonatal (3-day-old) and adult rats following acute and chronic treatment with phenytoin (PHT). Acutely, PHT significantly inhibited the enzyme Na+, K+-ATPase in both neonatal and adult rats. This effect was accompanied by a significant increase in cerebral cortical Na+ content and a decrease in K+ content only in neonatal animals. Chronic treatment (two and four times a day for 7 days) of adult rats with PHT significantly reduced Na+ content without affecting whole homogenate Na+, K+-ATPase activity. The activity of this enzyme was markedly increased in the myelin- (glial product) and slightly decreased in the synaptosomal- (neuronal) fractions following chronic (four times a day for 7 days) PHT treatment. These results suggest that PHT differentially affects the two forms (neuronal and glial) of the enzyme Na+, K+-ATPase. The possible relevance of this hypothesis in relationship to the anticonvulsant and excitatory properties of PHT is discussed. Chronic (two and four times a day for 7 days) PHT treatment increased both DNA content and activity of the glial marker enzyme carbonic anhydrase. Activity of the mitochondrial enzyme HCO3- -ATPase was also increased following chronic PHT treatment. These two enzymes are intimately involved in the regulation of HCO3- -Cl- transport across glial cell and mitochondrial membranes, and these results suggest that PHT is able to affect beneficially glial regulatory processes. The ability to enhance glial regulation of anions and cations in extracellular fluid provides new and important insights into the mechanism of the anticonvulsant action of PHT.     

Repeated injuries dramatically affect cells of the oligodendrocyte lineage: effects of PDGF and NT-3 in vitro

In multiple sclerosis, relapses occur and remyelination is incomplete, whereas one demyelinating lesion induced by lysophosphatidyl choline (LPC) in rats is completely remyelinated; this process is accelerated by platelet-derived growth factor (PDGF) (Allamargot et al.: Brain Res 918:28-39,2001) and neurotrophin-3 (NT-3) (Jean et al.: Brain Res 972:110-118,2003). Similarly, oligodendrocyte (OL) progenitors might not be depleted by two to three episodes of toxic demyelination (Penderis et al.: Brain 126:1382-1391,2003); nevertheless this does not allow conclusions about the fate of resident cells (mature OL). As myelinated fibers per OL are constantly decreased in chronic MS plaques (Fressinaud and Jean: J Neurochem 85(suppl):100, 2003), this suggests that OL decreased capability to synthesize new myelin membranes could result from successive relapses, impairing thereby remyelination. Thus, we have determined the consequences of multiple versus unique (Fressinaud and Vallat: J Neurosci Res 38:202-213, 1994) LPC treatments on newborn rat brain pure OL cultures, as well as the putative pro-remyelinating effects of PDGF and of NT-3 in these conditions. Split (0.5. 0(-5) M, 6 h x 4) and multiple (2.10(-5) M, 24 h x 2) LPC doses induced more cell loss than a unique treatment (2 x 10(-5) M, 24 h) and there was no recovery. OL progenitors (A2B5+ cells) and differentiated (CNP+) OL were drastically decreased. Moreover, mature (MBP+) OL disappeared from these cultures, indicating that mature OL are also vulnerable to multiple insults. PDGF, as well as NT-3, induced at least partial recovery, and enhanced OL progenitor proliferation. In cultures treated with either of these growth factors, mature OL represented one-fourth of cells and extended numerous ramified processes and putative myelin balls.     

Relationship between cortical lamination and texture sensitivity in complex neurones of the striate cortex in cats

The present study provides detailed anatomical evidence that the strongly texture-sensitive complex neurones of the cat's striate cortex constitute a discrete subset of all complex neurones, and lie in two bands, deep in lamina III and in lamina V. Physiological properties of simple and complex striate cortical neurones were characterized extracellularly in lightly anaesthetized cats by use of micropipettes filled with 12% Fast Green FCF dye in 2.0 M sodium chloride. Complex neurones were further subdivided on the basis of their length-summating properties for an optimally oriented bar into "standard," "special," or "intermediate" categories and on the basis of their tuning and degree of sensitivity to motion of random texture. Extracellular dye marks were made at strategic locations along each microelectrode track, especially at the site of recording from strongly texture-sensitive complex neurones. Tracks were reconstructed with the aid of the histologically recovered dye marks in sections counterstained with cresyl violet to reveal cortical lamination. The results confirm and refine the inference made by Hammond and MacKay (Exp. Brain Res. 22:427-430, '75; Exp. Brain Res. 30:275-296, '77) and the gross observations from 2-deoxyglucose uptake studies by Wagner, Hoffmann, and Zwerger (Brain Res. 224:31-43, '81) concerning the laminar distribution of texture-sensitive complex neurones in the cat's striate cortex.     

Single K+ channel properties in cultured mouse Schwann cells: conductance and kinetics

Cultured Schwann cells are characterized by a strong outward rectification of the membrane; the threshold of the outward currents is close to the resting membrane potential of about -50 mV (Gray et al.: In Ritchie, Keynes (eds): Ion Channels in Neural Membranes. New York: Alan R. Liss, Inc., pp 145-157, 1986). These outward currents show up a heterogeneity among the cultured Schwann cells: some cells displayed inactivating, others non-inactivating outward currents (Hoppe et al.: Pflügers Arch 415:22-28, 1989). In this study we characterized the single channel currents using the patch-clamp technique in the intact patch recording configuration. The conductance of all recorded channels was 10-12 pS (5.6 mM [K+]o). These channels were K+ selective since changes in extracellular [K+] resulted in changes of the reversal potential as predicted for an exclusively K+ selective pore. The reversal potentials also predicted an intracellular [K+] of 60 mM indicating that the K+ equilibrium potential is slightly negative to the membrane potential. Analysis of the kinetic behavior of the channels resolved two different types of behaviour: 40% inactivated during a depolarizing voltage step, the others showing no sign of inactivation. The analysis of open probability and gating properties in the steady state showed up more differences between these two channel types: mean open probability peaked at about 10 mV for inactivating channels, while it continuously increased for non-inactivating channels. The inactivation time constants of averaged single channel and whole cell currents were similar and showed both a similar voltage dependency. We conclude that cultured Schwann cells express either two types of K+ channels with similar conductance or a channel which can acquire two functional states and that these channels can account for the different types of K+ currents observed in these cells.     

Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal

Caffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139-170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129-135; Mulderink et al. [2002] Neuroimage 15:37-44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level-dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751-757; Mulderink et al. [2002] Neuroimage 15:37-44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine-related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620-640).     

Morphological changes of astroglia in the cerebellar cortex of developing mice after neonatal administration of cytosine arabinoside

Neonatal administration of cytosine arabinoside (Ara-C) induced marked hypoplasia of the mouse cerebellum. In 17-20-day-old mice with neonatal Ara-C injections, the external granular layer was still preserved as an irregular cell laminae in the superficial part of the cerebellum, in contrast to its complete disappearance in normal animals at these stages. Immunohistochemical examination using anti-glial fibrillary acidic protein and monoclonal antibody-1D11 (Ono et al: Dev. Brain Res., 50:154-159, 1989) demonstrated malformation of a palisade-like arrangement of labeled glial fibers in the superficial part of the Ara-C treated mouse cerebellum. Furthermore, the immunoreactive astroglia were observed just beneath the pial membrane and their processes were oriented to the deeper part of the molecular layer.     

A subpopulation of bone marrow-derived macrophage-like cells shares a unique ion channel pattern with microglia.

Rat microglia share a number of antigenic, functional, and morphological similarities with macrophages from other tissues, but are characterized by a distinctly different pattern of ion channels in the cellular membrane (Kettenmann et al., J Neurosci Res 26:278-287, 1990). Macrophages typically express outward and inward K+ currents. In contrast, microglia lack outward currents and only show inwardly rectifying K+ currents, regardless of the isolation or cultivation method employed for microglia. In this study we demonstrate that a subpopulation of bone marrow-derived macrophage-like cells possesses inward rectifier K+ currents, but no outward currents and thus with regard to the electrophysiological characteristics closely resembles microglia. A second population of bone marrow-derived macrophage-like cells shows the usual channel pattern described for other body macrophages. Our results strengthen the hypothesis that in the bone marrow distinct pools of precursor cells exist, possibly reflecting an early differential lineage determination for body and brain macrophages, i.e., microglia.     

Phenotypic analysis of mice deficient in the major myelin protein MOBP,and evidence for a novel Mobp isoform

The retinae and brains of larval and adult amphibians survive long-lasting anoxia; this finding suggests the presence of functional K(ATP) channels. We have previously shown with immunocytochemistry studies that retinal glial (Müller) cells in adult frogs express the K(ATP) channel and receptor proteins, Kir6.1 and SUR1, while retinal neurons display Kir6.2 and SUR2A/B (Skatchkov et al., 2001a: NeuroReport 12:1437-1441; Eaton et al., in press: NeuroReport). Using both immunocytochemistry and electrophysiology, we demonstrate the expression of Kir6.1/SUR1 (K(ATP)) channels in adult frog and tadpole Müller cells. Using conditions favoring the activation of K(ATP) channels (i.e., ATP- and spermine-free cytoplasm-dialyzing solution containing gluconate) in Müller cells isolated from both adult frogs and tadpoles, we demonstrate the following. First, using the patch-clamp technique in whole-cell recordings, tolbutamide, a blocker of K(ATP) channels, blocks nearly 100% of the transient and about 30% of the steady-state inward currents and depolarizes the cell membrane by 5-12 mV. Second, inside-out membrane patches display a single-channel inward current induced by gluconate (40 mM) and blocked by ATP (200 microM) at the cytoplasmic side. The channels apparently show two sublevels (each of approximately 27-32 pS) with a total of 85-pS maximal conductance at -80 mV; the open probability follows a two-exponential mechanism. Thus, functional K(ATP) channels, composed of Kir6.1/SUR1, are present in frog Müller cells and contribute a significant part to the whole-cell K+ inward currents in the absence of ATP. Other inwardly rectifying channels, such as Kir4.1 or Kir2.1, may mediate the remaining currents. K(ATP) channels may help maintain glial cell functions during ATP deficiency.     

Astrocytes in the hippocampus of patients with temporal lobe epilepsy display changes in potassium conductances

Functional properties of astrocytes were investigated with the patch-clamp technique in acute hippocampal brain slices obtained from surgical specimens of patients suffering from pharmaco-resistant temporal lobe epilepsy (TLE). In patients with significant neuronal cell loss, i.e. Ammon's horn sclerosis, the glial current patterns resembled properties characteristic of immature astrocytes in the murine or rat hippocampus. Depolarizing voltage steps activated delayed rectifier and transient K+ currents as well as tetrodotoxin-sensitive Na+ currents in all astrocytes analysed in the sclerotic human tissue. Hyperpolarizing voltages elicited inward rectifier currents that inactivated at membrane potentials negative to -130 mV. Comparative recordings were performed in astrocytes from patients with lesion-associated TLE that lacked significant histopathological hippocampal alterations. These cells displayed stronger inward rectification. To obtain a quantitative measure, current densities were calculated and the ratio of inward to outward K+ conductances was determined. Both values were significantly smaller in astrocytes from the sclerotic group compared with lesion-associated TLE. During normal development of rodent brain, astroglial inward rectification gradually increases. It thus appears reasonable to suggest that astrocytes in human sclerotic tissue return to an immature current pattern. Reduced astroglial inward rectification in conjunction with seizure-induced shrinkage of the extracellular space may lead to impaired spatial K+ buffering. This will result in stronger and prolonged depolarization of glial cells and neurons in response to activity-dependent K+ release, and may thus contribute to seizure generation in this particular condition of human TLE.     

Direct and indirect "cortico"-rubral and rubro-cerebellar cortical projections in the pigeon.

In birds the red nucleus is the most rostral cell group in the brain having projections to all levels of the spinal cord (Cabot et al., Prog. Brain Res., 57:79-108, 1982), but its sources of afferents are incompletely known. In order to determine these, a series retrograde and anterograde tracing experiments was carried out, largely with cholera toxin B-chain conjugated to horseradish peroxidase. The results show that a sparse and diffuse projection to the red nucleus arises from deep regions of the hyperstriatum accessorium (HA) of the anterior Wulst, and that a much more dense projection arises from the caudal part of the nucleus principalis precommissuralis and the medial part of the medial spiriform nucleus (SpMm). These last two sources were themselves shown to receive a substantial projection from HA of the anterior Wulst. The red nucleus was also shown to project upon the cerebellar cortex of lobule VI, and SpM upon the cerebellar cortex of lobules VI through IX (Karten and Finger, Brain Res., 102:335-338, 1976; Clarke, J. Comp. Neurol., 174:535-552, 1977). Double retrograde labelling experiments with fluorescein and rhodamine labelled latex microspheres injected into the cerebellar cortex and spinal cord showed that the rubrocerebellar cortical neurons are a different population from, although intermixed with, the rubrospinal neurons.     

GABA and tyrosine hydroxylase immunocytochemistry reveal different patterns of colocalization in retinal neurons of various vertebrates

Colocalization of GABA- and tyrosine hydroxylase-like immunoreactivity was studied in the retinae of various vertebrate species in order to ascertain whether the presumed coexistence of GABA and dopamine, reported earlier for mammals (Kosaka et al.: Exp. Brain Res. 66:191-210, '87: W?ssle and Chun: J. Neurosci. 8:3383-3394,'88) is a common phenomenon. GABA-immunopositive cells constituted a separate population from tyrosine hydroxylase-positive cells in fish and amphibians, whilst in higher--i.e., amniote--vertebrates, such as reptiles, birds, and mammals, all dopaminergic cells contained GABA-like immunoreactivity. No clear correlation was found between the type of dopaminergic cell (amacrine/interplexiform) and the presence or absence of colocalization.     

Endothelin Opens Potassium Channels in Glial Cells

Endothelin-1 (ET-1), an autocrine hormone synthesized by astrocytes, and endothelin-3 (ET-3), a highly homologous peptide produced by neurons, have both been shown previously to cause proliferation of these astrocytes in culture [Supattapone et al. (1989) Biochem. Biophys. Res. Commun., 165, 1115 - 1122; MacCumber et al. (1990) Proc. Natl. Acad. Sci. USA, 87, 2359 - 2363]. We now demonstrate, using 86Rb+ influx assays and single channel patch-clamp recording, that both endothelins-ET-3 and ET-1-can also open a charybdotoxin-sensitive, calcium-activated K+ channel of 15 - 40 pS in glial cells. The opening of this channel may be important for the regulation of [K+] in the brain microenvironment. Thus, the endothelins may be a general mediator of astroglial response to neuronal injury.