Identification of native rat cerebellar granule cell currents due to background K channel KCNK5 (TASK-2)

The TWIK-related, Acid Sensing K (TASK-2; KCNK5) potassium channel is a member of the tandem pore (2P) family of potassium channels and mediates an alkaline pH-activated, acid pH-inhibited, outward-rectified potassium conductance. In previous work, we demonstrated TASK-2 protein expression in newborn rat cerebellar granule neurons (CGNs). In this study, we demonstrate TASK-2 functional expression in CGNs as a component of the pH-sensitive, volatile anesthetic-potentiated, standing-outward potassium conductance (I(K,SO)). Using excised, inside-out patch-clamp technique, we studied CGNs grown in primary culture. We identified four distinct, noninactivating single channel potassium conductances, Types 1-4. Types 1-3 have previously been attributed to TASK-1 (KCNK3), TASK-3 (KCNK9) and TASK-1/TASK-3 heteromers, and TREK-2 (KCNK10) 2P potassium channel function, respectively; however, the Type 4 conductance is currently unassigned. Previous studies demonstrated that Type 4 single channel activity is potentiated by extracellular, alkaline pH and cytoplasmic arachidonic acid (10-20 microM) and inhibited by cytoplasmic tetraethylammonium (TEA; 1 mM). We determined that heterologously expressed TASK-2 channels have single channel gating, conductance properties and pH sensitivity identical to the Type 4 conductance. Additionally, we found that TASK-2 single channel activity, like the Type 4 conductance is potentiated by cytoplasmic arachidonic acid (20 microM) and inhibited by cytoplasmic TEA (1 mM). We conclude that TASK-2 mediates the Type 4 single channel conductance in CGNs as a component of I(K,SO).     

The TASK-1 two-pore domain K+ channel is a molecular substrate for neuronal effects of inhalation anesthetics.

Despite widespread use of volatile general anesthetics for well over a century, the mechanisms by which they alter specific CNS functions remain unclear. Here, we present evidence implicating the two-pore domain, pH-sensitive TASK-1 channel as a target for specific, clinically important anesthetic effects in mammalian neurons. In rat somatic motoneurons and locus coeruleus cells, two populations of neurons that express TASK-1 mRNA, inhalation anesthetics activated a neuronal K(+) conductance, causing membrane hyperpolarization and suppressing action potential discharge. These membrane effects occurred at clinically relevant anesthetic levels, with precisely the steep concentration dependence expected for anesthetic effects of these compounds. The native neuronal K(+) current displayed voltage- and time-dependent properties that were identical to those mediated by the open-rectifier TASK-1 channel. Moreover, the neuronal K(+) channel and heterologously expressed TASK-1 were similarly modulated by extracellular pH. The decreased cellular excitability associated with TASK-1 activation in these cell groups probably accounts for specific CNS effects of anesthetics: in motoneurons, it likely contributes to anesthetic-induced immobilization, whereas in the locus coeruleus, it may support analgesic and hypnotic actions attributed to inhibition of those neurons.     

Protective effects of TASK-3 (KCNK9) and related 2P K channels during cellular stress

Tandem pore domain (or 2P) K channels form a recently isolated family of channels that are responsible for background K currents in excitable tissues. Previous studies have indicated that 2P K channel activity produces membrane hyperpolarization, which may offer protection from cellular insults. To study the effect of these channels in neuroprotection, we overexpressed pH-sensitive 2P K channels by transfecting the partially transformed C8 cell line with these channels. Tandem pore weak inward rectifier K channel (TWIK)-related acid-sensitive K channel 3 (TASK-3, KCNK9) as well as other pH sensitive 2P K channels (TASK-1 and TASK-2) enhanced cell viability by inhibiting the activation of intracellular apoptosis pathways. To explore the cellular basis for this protection in a more complex cellular environment, we infected cultured hippocampal slices with Sindbis virus constructs containing the coding sequences of these channels. Expression of TASK-3 throughout the hippocampal structure afforded neurons within the dentate and CA1 regions significant protection from an oxygen-glucose deprivation (OGD) injury. Neuroprotection within TASK-3 expressing slices was also enhanced by incubation with isoflurane. These results confirm a protective physiologic capability of TASK-3 and related 2P K channels, and suggest agents that enhance their activity, such as volatile anesthetics may intensify these protective effects.     

Tandem-pore domain potassium channels are functionally expressed in retinal (Müller) glial cells

Tandem-pore domain (2P-domain) K+-channels regulate neuronal excitability, but their function in glia, particularly, in retinal glial cells, is unclear. We have previously demonstrated the immunocytochemical localization of the 2P-domain K+ channels TASK-1 and TASK-2 in retinal Müller glial cells of amphibians. The purpose of the present study was to determine whether these channels were functional, by employing whole-cell recording from frog and mammalian (guinea pig, rat and mouse) Müller cells and confocal microscopy to monitor swelling in rat Müller cells. TASK-like immunolabel was localized in these cells. The currents mediated by 2P-domain channels were studied in isolation after blocking Kir, K(A), K(D), and BK channels. The remaining cell conductance was mostly outward and was depressed by acid pH, bupivacaine, methanandamide, quinine, and clofilium, and activated by alkaline pH in a manner consistent with that described for TASK channels. Arachidonic acid (an activator of TREK channels) had no effect on this conductance. Blockade of the conductance with bupivacaine depolarized the Müller cell membrane potential by about 50%. In slices of the rat retina, adenosine inhibited osmotic glial cell swelling via activation of A1 receptors and subsequent opening of 2P-domain K+ channels. The swelling was strongly increased by clofilium and quinine (inhibitors of 2P-domain K+ channels). These data suggest that 2P-domain K+ channels are involved in homeostasis of glial cell volume, in activity-dependent spatial K+ buffering and may play a role in maintenance of a hyperpolarized membrane potential especially in conditions where Kir channels are blocked or downregulated.     

Tandem-pore K(+) channels display an uneven distribution in amphibian retina

Previous studies in retinal glial (Müller) cells have suggested that the dominant membrane currents are mediated by K(+) inward-rectifier (Kir) channels. After blockade of inwardly (Kir) and outwardly (KD and BK) conducting channels, a large K(+) conductance remains, but its nature has not been determined. Tandem-pore K(+) channels are likely candidates for this potassium conductance and the purpose of the present study was to determine, using immunocytochemistry, whether Müller cells express TASK-1, TASK-2, TREK-1 and/or TREK-2 potassium channel subunits. The results reveal that retinal glial cells express TASK-1 and TASK-2 subunits, but not TREK-1 or TREK-2 subunits. Furthermore, the distribution of TASK subunits differs from that of Kir channels and may contribute to the potassium conductance of Müller cells.     

Neuropeptide Y actions and the distribution of Ca2+-dependent Cl- conductance in rat dorsal root ganglion neurons

Neuropeptide Y (NPY) increases the excitability of 'small', nociceptive, dorsal root ganglion (DRG) neurons. This effect, which may contribute to the etiology of 'neuropathic' pain, has been attributed to attenuation of Ca2+-sensitive K+ conductance(s) (gK,Ca) following suppression of Ca2+ entry via N-type Ca2+ channels. A problem arises with this conclusion because rat DRG neurons normally contain high intracellular Cl- and some of them express a Ca2+-dependent Cl- conductance (gCl,Ca). In this study, we find that in rat DRG neurons increasing intracellular Cl- does not attenuate the effect of 1 microM NPY because gCl,Ca is not found in 'small' DRG cells and the peptide failed to affect the gCl,Ca found in 'large' cells. Thus, the presence of gCl,Ca in a subpopulation of 'large' DRG neurons does not alter the conclusion that excitatory effects of NPY result from attenuation of gK,Ca.     

Localization of the tandem pore domain K+ channel KCNK5 (TASK-2) in the rat central nervous system

Tandem pore domain K+ channels (2P K+ channels) are responsible for background K+ currents. 2P K+ channels are the most numerous encoded K+ channels in the Caenorhabditis elegans and Drosophila melanogaster genomes and to date 14 human 2P K+ channels have been identified. The 2P K+ channel TASK-2 (also named KCNK5) is sensitive to changes in extracellular pH, inhibited by local anesthetics and activated by volatile anesthetics. While TASK-1 has been shown to be involved in controlling neuronal cell excitability, much less is known about the cellular expression and function of TASK-2, originally cloned from human kidney. Previous studies demonstrated TASK-2 mRNA expression in high abundance in human kidney, liver, and pancreas, but only low expression in mouse brain or even absent expression in human brain was reported. In this study we have used immunohistochemical methods to localize TASK-2 at the cellular level in the rat central nervous system. TASK-2 immunoreactivity is prominently found in the rat hippocampal formation with the strongest staining observed in the pyramidal cell layer and in the dentate gyrus, and the Purkinje and granule cells of cerebellum. Additional immunofluorescence studies in cultured cerebellar granule cells demonstrate TASK-2 localization to the neuronal soma and to the proximal regions of neurites of cerebellar granule cells. The superficial layers of spinal cord and small-diameter neurons of dorsal root ganglia also showed strong TASK-2 immunoreactivity. These results suggest a possible involvement of TASK-2 in central mechanisms for controlling cell excitability and in peripheral signal transduction.     

Postnatal changes in TASK-1 and TREK-1 expression in rat brain stem and cerebellum

Developmental changes in expression of two-pore domain K+ channels, TASK-1 and TREK-1, were investigated in the juvenile (postnatal day 13; P13) and adult (P105) rat brain stem and cerebellum using immunohistochemistry. In the juvenile, extensive TASK-1-like immunoreactivity (TASK-1-LIR) was seen among glial cells in the white matter (e.g., radial glia), which showed marked reduction in the adult. In contrast, TASK-1-LIR in neurons including cerebellar Purkinje and granule cells, hypoglossal and facial motoneurons, and ventrolateral medulla neurons was increased in the adult. TASK-1-LIR in neuroglia surrounding peripheral axons of cranial nerves was persistent. TREK-1-LIR was similar between ages, although TREK-1-LIR was neuronal and present only in juvenile cerebellar external germinal layer. Present results suggest roles for TASK-1 and K+ homeostasis in neuro-glial interaction, neurogenesis, differentiation, migration, axon guidance, synaptogenesis and myelination.     

Effect of catecholamines on the hyperpolarization-activated cationic Ih and the inwardly rectifying potassium I(Kir) currents in the rat substantia nigra pars compacta

Whole-cell ruptured-patch and perforated-patch recordings were used in principal neurons of the rat substantia nigra pars compacta (SNc) to study the effect of catecholamines both on the hyperpolarization-activated cationic (Ih) and the inwardly rectifying potassium (I(Kir)) currents. In internal potassium, a 2 min bath application of noradrenaline (NA; 50 microM) or dopamine (DA; 50 microM) both inhibited Ih and induced an outward current associated with an increase in I(Kir) conductance. These two effects recovered poorly after wash-out. Protein kinase A (PKA), protein kinase C (PKC) and phosphatases 1 and 2A inhibitors did not modify the NA and DA effects on the amplitude of Ih and I(Kir) currents. They also had no effect on the recovery of the catecholamine responses. In perforated-patch experiments, NA and DA also induced an inhibition of Ih and revealed an outward current associated with an increase in conductance. However, both effects recovered in less than 5 min following the wash-out. These results indicate that neither PKA, PKC, nor phosphatases 1 or 2A were required in the NA and DA modulation of these two currents and that an intracellular factor, that could be either washed-out or inversely up-regulated in the ruptured-patch configuration, was implicated in the recovery of both effects. In the presence of external barium (300 microM) or internal caesium which both blocked the outward current and the increase in conductance, neither NA nor DA affected Ih, suggesting that the effect on Ih observed is secondary to the activation of the I(Kir) channels. Increasing chloride conductance of the cell by activation of GABA(A) receptors also induced an inhibition of Ih. All together these results suggest that the NA or DA induced inhibition of Ih could result from an occlusion of Ih by a space-clamp effect.     

D2 dopamine receptor activation of potassium channels in identified rat lactotrophs: whole-cell and single-channel recording.

Dopamine (DA) is the major physiological regulator of prolactin secretion from the anterior pituitary, exerting a tonic inhibitory control that is mediated by D2 DA receptors. D2 receptors in both the anterior pituitary and CNS are thought to produce some of their inhibitory effects via a coupling to potassium (K+) channels to increase K+ conductance. Utilizing the reverse hemolytic plaque assay and patch-clamp techniques, we characterize the actions of DA on membrane potential and associated DA-activated whole-cell current, as well as the single K+ channels that underlie the response in primary rat lactotrophs. We demonstrate that DA (5 nM to 1 microM) or D2-selective agonists (RU24213 and quinpirole) evoke a hyperpolarization of membrane potential that was blocked by D2 antagonists and associated with an increased K+ conductance. Whole-cell current responses to ramp voltage commands revealed a DA-activated current whose reversal potential was near the calculated Nernst potential for K+, varied as a function of K+ concentration, exhibited some inward rectification, and was Ca2+ independent. The current was insensitive to tetraethylammonium (TEA; 10 mM), partially blocked by 4-aminopyridine (4-AP; 5 mM), and almost completely inhibited by quinine (100 microM). Cell-attached recordings in the presence of DA or a D2 agonist revealed the opening of a K+ channel that was not present in the absence of DA or when a D2 receptor antagonist was included with DA. Analysis of the single-channel current showed the current-voltage relationship to be linear at negative patch potentials and yielded a unitary conductance of 40.2 pS in the presence of 150 mM KCl. The channels were not blocked by TEA (10 mM), were slightly suppressed by 4-AP (5 mM), and were almost completely inhibited by quinine (100 microM). These experiments establish that in primary rat lactotrophs, DA acts at D2 receptors to activate the opening of single K+ channels, which results in an increase in K+ conductance and associated membrane hyperpolarization. This is the first characterization of single DA-activated K+ channels in an endocrine cell.     

Stimulatory effects of chlorzoxazone,a centrally acting muscle relaxant,on large conductance calcium-activated potassium channels in pituitary GH3 cells

Chlorzoxazone, a centrally acting muscle relaxant, has been used as a marker for hepatic CYP2E1 activity. However, little is known about the mechanism of chlorzoxazone actions on ion currents in neurons or neuroendocrine cells. We thus investigated its effects on ion currents in GH(3) lactotrophs. Chlorzoxazone reversibly increased Ca(2+)-activated K(+) current (I(K(Ca))) in a concentration-dependent manner with an EC(50) value of 30 microM. The chlorzoxazone-stimulated I(K(Ca)) was inhibited by iberitoxin (200 nM) or clotrimazole (10 microM), but not by glibenclamide (10 microM) or apamin (200 nM). Chlorzoxazone (30 microM) suppressed voltage-dependent L-type Ca(2+) current. In the inside-out configuration, chlorzoxazone applied to the intracellular side of the patch did not modify single-channel conductance of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, but did increase channel activity by increasing mean open time and decreasing mean closed time. Chlorzoxazone also caused a left shift in the activation curve of BK(Ca) channels. However, Ca(2+)-sensitivity of these channels was unaffected by chlorzoxazone. 1-Ethyl-2-benzimidazolinone (30 microM), 2-amino-5-chlorobenzoxazole (30 microM) or chlormezanone (30 microM) enhanced BK(Ca) channel activity, while 6-hydroxychlorzoxazone (30 microM) slightly increased it; however, chlorphenesin carbamate (30 microM) had no effect on it. Under the current-clamp condition, chlorzoxazone (10 microM) reduced the firing rate of action potentials. In neuroblastoma IMR-32 cells, chlorzoxazone (30 microM) also stimulated BK(Ca) channel activity. The stimulatory effects of chlorzoxazone on these channels may be responsible for the underlying mechanism of chlorzoxazone actions on neurons and neuroendocrine cells.     

On the role of calcium ions in the presynaptic alpha-receptor mediated inhibition of [3H]noradrenaline release from rat brain cortex synaptosomes

Rat brain cortex synaptosomes, previously labeled by incubation with [3H]noradrenaline ([3H]NA) were continuously superfused with Krebs-Ringer media. Release of [3H]NA was induced by superfusion with medium containing either 15 mM K+, 20 microM veratrine or 1 microM of the calcium-ionophore A 23187 and was strongly dependent on the concentration of Ca2+ in the medium. Noradrenaline (1 microM, in the presence of the uptake inhibitor desipramine) inhibited K+-induced [3H]NA release by activation of presynaptic alpha-receptors. When the Ca2+-concentration in the medium was reduced, or the Mg2+-concentration increased, [3H]NA release appeared to be more susceptible to alpha-receptor mediated inhibition. Noradrenaline (1 microM) inhibited [3H]NA release induced by 15 mM K+, in the presence of 0.075 Ca2+ and 10 mM Mg2+, by 86%. Veratrine-induced release was also inhibited by alpha-receptor activation. However, [3H]NA release induced by the calcium-ionophore was not affected by alpha-receptor agonists. These results strongly support the view that alpha-receptor activation results in a decrease of the availability of Ca2+ for stimulus-secretion coupling processes. Presumably this is effected by an inhibition of voltage-sensitive calcium channels in the neuronal membrane associated with neurotransmitter release.     

Inhibition of a cAMP-dependent Ca-activated K conductance by forskolin prolongs Ca action potential duration in lamprey sensory neurons

Intracellular recordings from primary mechanosensory neurons (dorsal cells) of the lamprey spinal cord were made to test the membrane effects of forskolin, an activator of adenylate cyclase in these cells. At a concentration of 50 microM, forskolin was found to have a pronounced broadening effect on calcium action potentials (Ca APs) produced in the presence of voltage-activated K channel blockers (TEA, 3,4-DAP). Forskolin had no effect on passive membrane properties of the cells, such as resting potential or input resistance. Nor did it affect delayed rectification or Na APs and thus appeared not to block voltage-activated K channels. Forskolin's effect was evident only when a significant Ca component to the AP was present. It appeared not to increase the conductance of the Ca channel since its action was accompanied by a decrease in membrane conductance during the Ca AP, indicating instead an inhibition of a repolarizing Ca-activated conductance, other than a Ca-activated Cl conductance. The prolongation of Ca APs by forskolin, barium or the neurotransmitter GABA were all correlated in voltage-clamp with a decrease in outward current. Under the conductions used here, the major outward conductance in dorsal cells is a Ca-activated K conductance (gK(Ca]28, and it is concluded that the most probable mode of action for forskolin is via a cyclic AMP-mediated inhibition of this conductance. GABA has also been shown to prolong Ca APs in lamprey dorsal cells by inhibiting a repolarizing gK(Ca)28. Thus, the action of this transmitter may be mediated by an increase in intracellular cyclic AMP.     

Effect of vasopressin on the input–output properties of rat facial motoneurons

Vasopressin can directly excite facial motoneurons in young rats and mice. It acts by generating a persistent inward current, which is Na(+)-dependent, tetrodotoxin-insensitive and voltage-gated. This peptide-evoked current is unaffected by Ca(++) or K(+) channel blockade and is modulated by extracellular divalent cations. In the present work, we determined how vasopressin alters the input-output properties of facial motoneurons. Whole-cell recordings were obtained from these neurons in the current clamp mode, in brainstem slices of young rats. Repetitive firing was evoked by injecting depolarizing current pulses. Steady-state frequency-current (f-I) relationships were constructed and the effect of vasopressin on these relationships was studied. We found that vasopressin caused a parallel shift to the left of the cell steady-state f-I relationship. This effect persisted in the presence of blockers of K(+) or Ca(++) channels. The peptide effect was distinct from that brought about by Ca(++) channel suppression or by apamin, a blocker of the mAHP. These latter manipulations resulted in an increase in the slope of the steady-state f-I relationship. We conclude that the vasopressin-induced modification of the input-output properties of facial motoneurons is probably exclusively caused by the sodium-dependent, voltage-modulated inward current elicited by the peptide, rather than being due to indirect effects of the peptide on Ca(++) channels, K(+) channels or Ca(++)-dependent K(+) channels. Computer simulation, based on a simple model of facial motoneurons, indicates that the introduction of a conductance having the properties of the vasopressin-dependent conductance can entirely account for the observed peptide-induced shift of the f-I relationship.     

Excitability of pontine startle processing neurones is regulated by the two-pore-domain K+ channel TASK-3 coupled to 5-HT2C receptors

The mammalian startle reflex is a fast response to sudden intense sensory stimuli that can be increased by anxiety or decreased by reward. The cellular integration of sensory and modulatory information takes place in giant neurones of the caudal pontine reticular formation (PnC). The startle reflex is known to be enhanced by 5-hydroxytryptamine (5-HT); however, signalling mechanisms that change the excitability of the PnC giant neurones are poorly understood. Possible molecular candidates are two-pore-domain K⁺ (K₂P) channels that generate a variable K⁺ background conductance and control neuronal excitability upon activation of G-protein-coupled receptors. We demonstrate by in situ hybridization that the K₂P channel TASK-3 is substantially expressed in PnC giant neurones. Brain slice recordings revealed a corresponding background K⁺ current in these cells that forms about 30% of the outward current at −30 mV. Inactivation of TASK-3 at pH 6.4 and by ruthenium red depolarized the cells by about 7 mV and increased the action potential frequency as well as duration. Specific activation of Gα_q-coupled 5-HT₂ receptors with α-methyl 5-HT evoked a similar increase of neuronal excitability. Consistently, we measured afferent synaptic inputs from serotonergic raphe neurones and detected 5-HT_2C receptors in PnC giant neurones by immunohistochemistry. Thus, neuronal excitability of PnC giant neurones in vivo is most likely increased by serotonergic projections via the K₂P channel TASK-3.     

Galanin and Glibenclamide Modulate the Anoxic Release of Glutamate in Rat CA3 Hippocampal Neurons

The effects of brief anoxic episodes on intracellularly recorded CA3 pyramidal neurons have been studied in the hippocampal slice preparation. Anoxia induced a depolarization occasionally preceded by a transient hyperpolarization associated with a fall in input resistance. The anoxic depolarization was due to the release of glutamate from presynaptic terminals since it was blocked by tetrodotoxin (TTX) (1 microM) or by the broad spectrum excitatory amino acid antagonist kynurenate (1 mM). In the presence of TTX (1 microM) or kynurenate (1 mM), anoxia only induced a hyperpolarization which was due to activation of a K+ conductance. The anoxic depolarization was blocked by galanin, a hormone which activates ATP sensitive K+ (K+ATP) channels. Anoxic depolarization was increased by the potent sulfonylurea agent glibenclamide (GLIB) which blocks K+ATP channels. Bath applications of these agents had little effect when applied in oxygenated Krebs solution suggesting that their action may be mediated by K+ATP channels. Since excessive release of glutamate during anoxia is neurotoxic, agents such as galanin which activate K+ATP channels may provide tissue specific protection against anoxic damage.     

Interaction of phencyclidine with voltage-dependent potassium channels in cultured rat hippocampal neurons: comparison with block of the NMDA receptor-ionophore complex

Whole-cell voltage-clamp recording techniques were used to investigate the blockade of voltage-dependent K+ channels by phencyclidine (PCP) in cultured rat hippocampal neurons. All recordings were carried out in the presence of tetrodotoxin (1-2 microM) to eliminate Na+ currents. Step depolarization from a holding potential of -40 mV activated a slowly rising, minimally inactivating K+ current (IK). PCP (0.5-1000 microM) caused a reduction in the maximum conductance of IK [IC50(+30 mV), 22 microM] without altering its voltage dependency. The PCP block of IK diminished at depolarized potentials. Analysis according to the scheme of Woodhull (1973) suggested that block occurs via binding to an acceptor site (presumably within the channel pore) that senses 40-50% of the transmembrane electrostatic field. PCP had no effect on the kinetic properties of IK and the block failed to show use dependency, suggesting that PCP may bind to the IK channel via a hydrophobic mechanism not requiring open channels. For comparison, we also investigated the effect of PCP on the transient K+ current, IA, activated by step depolarization following a 200 msec prepulse to -90 mV (20 mM tetraethylammonium was present in the bathing solution to reduce IK). In contrast to the potent blocking action of PCP on IK, the drug only affected IA at high concentrations [IC50(+30 mV), 224 microM]. At concentrations causing substantial block (300-500 microM), PCP produced an acceleration in the IA inactivation rate, and, for brief (5-6 msec) depolarizing steps, the suppression of IA was use dependent. These observations suggest that PCP block of IA requires open channels. PCP reduced inward current responses induced by the excitatory amino acid agonist N-methyl-D-aspartate (NMDA) at substantially lower concentrations than those required for its effects on K+ channels [IC50(-60 mV), 0.45 microM]. The PCP-like dioxadrol stereoisomer dexoxadrol (10 microM) blocked NMDA-evoked inward current responses, while its behaviorally inactive enantiomer levoxadrol did not. Dexoxadrol and levoxadrol also blocked IK in a stereoselective fashion (IC50's, 73 and 260 microM, respectively), whereas the sigma ligands (+)- and (-)-SKF 10,047 and (+)-3-[3-hydroxyphenyl]-N-(1-propyl)piperidine [(+)-3-PPP] had little effect on the current (IC50's, greater than 300-500 microM). We conclude that PCP causes a selective, voltage-dependent block of IK in hippocampal neurons via a PCP- and not a sigma-type acceptor site.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ionic mechanism of the outward current induced by extracellular ejection of interleukin-1 onto identified neurons of Aplysia.

The ionic mechanism of the effect of extracellularly ejected recombinant human interleukin-1-beta (rhIL-1) on the membrane of identified neurons R9 and R10 of Aplysia was investigated with voltage-clamp, micropressure-ejection, and ion substitution techniques. Micropressure-ejected rhIL-1 caused a marked hyperpolarization in the unclamped neuron. Clamping the same neuron at its resting potential level (-60 mV) and reejecting rhIL-1 with the same dose produced a slow outward current (I0(IL-1), 20-30 s in duration, 3-5 nA in amplitude) associated with a decrease in input membrane conductance. I0(IL-1) was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of I0(IL-1) was approximately +15 mV. I0(IL-1) was sensitive to changes in the external Na+ concentration but not to changes in K+, Ca2+ and Cl- concentrations, and was resistant to tetraethylammonium (5 mM) and 4-aminopyridine (5 mM). Neither perfusion of the neuron with 50 microM tetrodotoxin nor perfusion with 10 mM Co2+ seawater caused any changes in I0(IL-1). I0(IL-1) was partially reduced by 50 microM ouabain. These results suggest that extracellular IL-1 can induce a slow outward current associated with a decrease in Na+ conductance and the immunomodulator IL-1 can act directly on the nervous system as well as on the immune system.