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Ceballos CC, Ma L, Qin M, Zhong H. Widespread co-release of glutamate and GABA throughout the mouse brain. Commun Biol 2024; 7:1502. [PMID: 39537846 PMCID: PMC11560972 DOI: 10.1038/s42003-024-07198-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2024] [Accepted: 11/01/2024] [Indexed: 11/16/2024] Open
Abstract
Several brain neuronal populations transmit both the excitatory and inhibitory neurotransmitters, glutamate, and GABA. However, it remains largely unknown whether these opposing neurotransmitters are co-released simultaneously or are independently transmitted at different times and locations. By recording from acute mouse brain slices, we observed biphasic miniature postsynaptic currents, i.e., minis with time-locked excitatory and inhibitory currents, in striatal spiny projection neurons. This observation cannot be explained by accidental coincidence of monophasic excitatory and inhibitory minis. Interestingly, these biphasic minis could either be an excitatory current leading an inhibitory current or vice versa. Deletion of dopaminergic neurons did not eliminate biphasic minis, indicating that they originate from another source. Importantly, we found that both types of biphasic minis were present in multiple striatal neuronal types and in nine out of ten other brain regions. Overall, co-release of glutamate and GABA appears to be a widespread mode of neurotransmission in the brain.
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Affiliation(s)
- Cesar C Ceballos
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
| | - Lei Ma
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
| | - Maozhen Qin
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA
| | - Haining Zhong
- Vollum Institute, Oregon Health & Science University, Portland, OR, USA.
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2
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Ceballos CC, Ma L, Qin M, Zhong H. Prevalent co-release of glutamate and GABA throughout the mouse brain. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.27.587069. [PMID: 38585864 PMCID: PMC10996720 DOI: 10.1101/2024.03.27.587069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
Several neuronal populations in the brain transmit both the excitatory and inhibitory neurotransmitters, glutamate, and GABA, to downstream neurons. However, it remains largely unknown whether these opposing neurotransmitters are co-released onto the same postsynaptic neuron simultaneously or are independently transmitted at different time and locations (called co-transmission). Here, using whole-cell patch-clamp recording on acute mouse brain slices, we observed biphasic miniature postsynaptic currents, i.e., minis with time-locked excitatory and inhibitory currents, in striatal spiny projection neurons (SPNs). This observation cannot be explained by accidental coincidence of monophasic miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs, respectively), arguing for the co-release of glutamate and GABA. Interestingly, these biphasic minis could either be an mEPSC leading an mIPSC or vice versa. Although dopaminergic axons release both glutamate and GABA in the striatum, deletion of dopamine neurons did not eliminate biphasic minis, indicating that the co-release originates from another neuronal type. Importantly, we found that both types of biphasic minis were detected in other neuronal subtypes in the striatum as well as in nine out of ten additionally tested brain regions. Our results suggest that co-release of glutamate and GABA is a prevalent mode of neurotransmission in the brain.
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Affiliation(s)
- Cesar C Ceballos
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Lei Ma
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Maozhen Qin
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Haining Zhong
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA
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Zhang Y, Glowatzki E, Roux I, Fuchs PA. Nicotine evoked efferent transmitter release onto immature cochlear inner hair cells. J Neurophysiol 2020; 124:1377-1387. [PMID: 32845208 DOI: 10.1152/jn.00097.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Olivocochlear neurons make temporary cholinergic synapses on inner hair cells of the rodent cochlea in the first 2 to 3 wk after birth. Repetitive stimulation of these efferent neurons causes facilitation of evoked release and increased spontaneous release that continues for seconds to minutes. Presynaptic nicotinic acetylcholine receptors (nAChRs) are known to modulate neurotransmitter release from brain neurons. The present study explores the hypothesis that presynaptic nAChRs help to increase spontaneous release from efferent terminals on cochlear hair cells. Direct application of nicotine (which does not activate the hair cells' α9α10-containing nAChRs) produces sustained efferent transmitter release, implicating presynaptic nAChRs in this response. The effect of nicotine was reduced by application of ryanodine that reduces release of calcium from intraterminal stores.NEW & NOTEWORTHY Sensory organs exhibit spontaneous activity before the onset of response to external stimuli. Such activity in the cochlea is subject to modulation by cholinergic efferent neurons that directly inhibit sensory hair cells (inner hair cells). Those efferent neurons are themselves subject to various modulatory mechanisms. One such mechanism is positive feedback by released acetylcholine onto presynaptic nicotinic acetylcholine receptors causing further release of acetylcholine.
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Affiliation(s)
- Y Zhang
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - E Glowatzki
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - I Roux
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Otolaryngology Branch, National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health, Porter Neuroscience Research Center, Bethesda, Maryland
| | - P A Fuchs
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
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Yaeger DB, Coddington EJ. Calcium-induced calcium release activates spontaneous miniature outward currents in newt medullary reticular formation neurons. J Neurophysiol 2018; 120:3140-3154. [PMID: 29897864 DOI: 10.1152/jn.00616.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Neurons in the medullary reticular formation are involved in the control of postural and locomotor behaviors in all vertebrates. Reticulospinal neurons in this brain region provide one of the major descending projections to the spinal cord. Although neurons in the newt medullary reticular formation have been extensively studied using in vivo extracellular recordings, little is known of their intrinsic biophysical properties or of the underlying circuitry of this region. Using whole cell patch-clamp recordings in brain slices containing the rostromedial reticular formation from adult male newts, we observed spontaneous miniature outward currents (SMOCs) in ~2/3 of neurons. Although SMOCs superficially resembled inhibitory postsynaptic currents (IPSCs), they had slower risetimes and decay times than spontaneous IPSCs. SMOCs required intracellular Ca2+ release from ryanodine receptors and were also dependent on the influx of extracellular Ca2+. SMOCs were unaffected by apamin but were partially blocked by iberiotoxin and charybdotoxin, indicating that SMOCs were mediated by big-conductance Ca2+-activated K+ channels. Application of the sarco/endoplasmic Ca2+ ATPase inhibitor cyclopiazonic acid blocked the generation of SMOCs and also increased neural excitability. Neurons with SMOCs had significantly broader action potentials, slower membrane time constants, and higher input resistance than neurons without SMOCs. Thus, SMOCs may serve as a mechanism to regulate action potential threshold in a majority of neurons within the newt medullary reticular formation. NEW & NOTEWORTHY The medullary reticular formation exerts a powerful influence on sensorimotor integration and subsequent motor behavior, yet little is known about the neurons involved. In this study, we identify a transient potassium current that regulates action potential threshold in a majority of medullary reticular neurons.
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Irie T, Trussell LO. Double-Nanodomain Coupling of Calcium Channels, Ryanodine Receptors, and BK Channels Controls the Generation of Burst Firing. Neuron 2017; 96:856-870.e4. [PMID: 29144974 DOI: 10.1016/j.neuron.2017.10.014] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 06/21/2017] [Accepted: 10/06/2017] [Indexed: 01/16/2023]
Abstract
Action potentials clustered into high-frequency bursts play distinct roles in neural computations. However, little is known about ionic currents that control the duration and probability of these bursts. We found that, in cartwheel inhibitory interneurons of the dorsal cochlear nucleus, the likelihood of bursts and the interval between their spikelets were controlled by Ca2+ acting across two nanodomains, one between plasma membrane P/Q Ca2+ channels and endoplasmic reticulum (ER) ryanodine receptors and another between ryanodine receptors and large-conductance, voltage- and Ca2+-activated K+ (BK) channels. Each spike triggered Ca2+-induced Ca2+ release (CICR) from the ER immediately beneath somatic, but not axonal or dendritic, plasma membrane. Moreover, immunolabeling demonstrated close apposition of ryanodine receptors and BK channels. Double-nanodomain coupling between somatic plasma membrane and hypolemmal ER cisterns provides a unique mechanism for rapid control of action potentials on the millisecond timescale.
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Affiliation(s)
- Tomohiko Irie
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR 97239, USA; Division of Pharmacology, National Institute of Health Sciences, Kanagawa 210-9501, Japan.
| | - Laurence O Trussell
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR 97239, USA; Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA.
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Saito Y, Yanagawa Y. Ca(2+)-activated ion currents triggered by ryanodine receptor-mediated Ca(2+) release control firing of inhibitory neurons in the prepositus hypoglossi nucleus. J Neurophysiol 2012; 109:389-404. [PMID: 23100137 DOI: 10.1152/jn.00617.2012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous miniature outward currents (SMOCs) are known to exist in smooth muscles and peripheral neurons, and evidence for the presence of SMOCs in central neurons has been accumulating. SMOCs in central neurons are induced through Ca(2+)-activated K(+) (K(Ca)) channels, which are activated through Ca(2+)-induced Ca(2+) release from the endoplasmic reticulum via ryanodine receptors (RyRs). Previously, we found that some neurons in the prepositus hypoglossi nucleus (PHN) showed spontaneous outward currents (SOCs). In the present study, we used whole cell recordings in slice preparations of the rat brain stem to investigate the following: 1) the ionic mechanisms of SOCs, 2) the types of neurons exhibiting frequent SOCs, and 3) the effect of Ca(2+)-activated conductance on neuronal firing. Pharmacological analyses revealed that SOCs were induced via the activation of small-conductance-type K(Ca) (SK) channels and RyRs, indicating that SOCs correspond to SMOCs. An analysis of the voltage responses to current pulses of the fluorescence-expressing inhibitory neurons of transgenic rats revealed that inhibitory neurons frequently exhibited SOCs. Abolition of SOCs via blockade of SK channels enhanced the frequency of spontaneous firing of inhibitory PHN neurons. However, abolition of SOCs via blockade of RyRs reduced the firing frequency and hyperpolarized the membrane potential. Similar reductions in firing frequency and hyperpolarization were also observed when Ca(2+)-activated nonselective cation (CAN) channels were blocked. These results suggest that, in inhibitory neurons in the PHN, Ca(2+) release via RyRs activates SK and CAN channels, and these channels regulate spontaneous firing in a complementary manner.
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Affiliation(s)
- Yasuhiko Saito
- Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
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Kaufmann WA, Kasugai Y, Ferraguti F, Storm JF. Two distinct pools of large-conductance calcium-activated potassium channels in the somatic plasma membrane of central principal neurons. Neuroscience 2010; 169:974-86. [PMID: 20595025 PMCID: PMC2923744 DOI: 10.1016/j.neuroscience.2010.05.070] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2010] [Revised: 05/26/2010] [Accepted: 05/27/2010] [Indexed: 01/07/2023]
Abstract
Although nerve cell membranes are often assumed to be uniform with respect to electrical properties, there is increasing evidence for compartmentalization into subdomains with heterogeneous impacts on the overall cell function. Such microdomains are characterized by specific sets of proteins determining their functional properties. Recently, clustering of large-conductance calcium-activated potassium (BKCa) channels was shown at sites of subsurface membrane cisterns in cerebellar Purkinje cells (PC), where they likely participate in building a subcellular signaling unit, the 'PLasmERosome'. By applying SDS-digested freeze-fracture replica labeling (SDS-FRL) and postembedding immunogold electron microscopy, we have now studied the spatial organization of somatic BKCa channels in neocortical layer 5 pyramidal neurons, principal neurons of the central and basolateral amygdaloid nuclei, hippocampal pyramidal neurons and dentate gyrus (DG) granule cells to establish whether there is a common organizational principle in the distribution of BKCa channels in central principal neurons. In all cell types analyzed, somatic BKCa channels were found to be non-homogenously distributed in the plasma membrane, forming two pools of channels with one pool consisting of clustered channels and the other of scattered channels in the extrasynaptic membrane. Quantitative analysis by means of SDS-FRL revealed that about two-thirds of BKCa channels belong to the scattered pool and about one-third to the clustered pool in principal cell somata. Overall densities of channels in both pools differed in the different cell types analyzed, although being considerably lower compared to cerebellar PC. Postembedding immunogold labeling revealed association of clustered channels with subsurface membrane cisterns and confirmed extrasynaptic localization of scattered channels. This study indicates a common organizational principle for somatic BKCa channels in central principal neurons with the formation of a clustered and a scattered pool of channels, and a cell-type specific density of this channel type.
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Affiliation(s)
- W A Kaufmann
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr Strasse 1a, 6020 Innsbruck, Austria.
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8
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Klement G, Druzin M, Haage D, Malinina E, Arhem P, Johansson S. Spontaneous ryanodine-receptor-dependent Ca2+-activated K+ currents and hyperpolarizations in rat medial preoptic neurons. J Neurophysiol 2010; 103:2900-11. [PMID: 20457857 DOI: 10.1152/jn.00566.2009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of the present study was to clarify the identity of slow spontaneous currents, the underlying mechanism and possible role for impulse generation in neurons of the rat medial preoptic nucleus (MPN). Acutely dissociated neurons were studied with the perforated patch-clamp technique. Spontaneous outward currents, at a frequency of approximately 0.5 Hz and with a decay time constant of approximately 200 ms, were frequently detected in neurons when voltage-clamped between approximately -70 and -30 mV. The dependence on extracellular K(+) concentration was consistent with K(+) as the main charge carrier. We concluded that the main characteristics were similar to those of spontaneous miniature outward currents (SMOCs), previously reported mainly for muscle fibers and peripheral nerve. From the dependence on voltage and from a pharmacological analysis, we concluded that the currents were carried through small-conductance Ca(2+)-activated (SK) channels, of the SK3 subtype. From experiments with ryanodine, xestospongin C, and caffeine, we concluded that the spontaneous currents were triggered by Ca(2+) release from intracellular stores via ryanodine receptor channels. An apparent voltage dependence was explained by masking of the spontaneous currents as a consequence of steady SK-channel activation at membrane potentials > -30 mV. Under current-clamp conditions, corresponding transient hyperpolarizations occasionally exceeded 10 mV in amplitude and reduced the frequency of spontaneous impulses. In conclusion, MPN neurons display spontaneous hyperpolarizations triggered by Ca(2+) release via ryanodine receptors and SK3-channel activation. Thus such events may affect impulse firing of MPN neurons.
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Affiliation(s)
- Göran Klement
- Department of Integrative Medical Biology, Section for Physiology, Umeå University, Umeå, Sweden
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Cui G, Okamoto T, Morikawa H. Spontaneous opening of T-type Ca2+ channels contributes to the irregular firing of dopamine neurons in neonatal rats. J Neurosci 2005; 24:11079-87. [PMID: 15590924 PMCID: PMC1454359 DOI: 10.1523/jneurosci.2713-04.2004] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
During early postnatal development, midbrain dopamine (DA) neurons display anomalous firing patterns and amphetamine response. Spontaneous miniature hyperpolarizations (SMHs) are observed in DA neurons during the same period but not in adults. These hyperpolarizations have been shown to be dependent on the release of Ca2+ from internal stores and the subsequent activation of Ca2+-sensitive K+ channels. However, the triggering mechanism and the functional significance of SMHs remain poorly understood. To address these issues, using brain slices, we recorded spontaneous miniature outward currents (SMOCs) in DA neurons of neonatal rats. Two types of SMOCs were identified based on the peak amplitude. Both types were suppressed by intracellular dialysis of ruthenium red, a ryanodine receptor (RyR) antagonist, yet none of the known Ca2+-releasing messengers were involved. T-type Ca2+ channel blockers (Ni2+ and mibefradil) inhibited large-amplitude SMOCs without affecting the small-amplitude ones. The voltage dependence of SMOCs displayed a peak of approximately -50 mV, consistent with the involvement of low-threshold T-type Ca2+ channels. Blockade of SMOCs with cyclopiazonic acid or ryanodine converted the irregular firing of DA neurons in neonatal rats into an adult-like pacemaker pattern. This effect was reversed by the injection of artificial currents mimicking SMOCs. Finally, amphetamine inhibited SMOCs and transformed the irregular firing pattern into a more regular one. These data demonstrate that Ca2+ influx through T-type Ca2+ channels, followed by Ca2+-induced Ca2+ release via RyRs, contributes to the generation of SMOCs. We propose that SMOCs-SMHs may underlie the anomalous firing and amphetamine response of DA neurons during the postnatal developmental period.
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Affiliation(s)
- Guohong Cui
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology and Institute for Neuroscience, University of Texas, Austin, Texas 78712, USA
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Barstow KL, Locknar SA, Merriam LA, Parsons RL. The modulation of action potential generation by calcium-induced calcium release is enhanced by mitochondrial inhibitors in mudpuppy parasympathetic neurons. Neuroscience 2004; 124:327-39. [PMID: 14980383 DOI: 10.1016/j.neuroscience.2003.12.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2003] [Revised: 12/05/2003] [Accepted: 12/11/2003] [Indexed: 11/29/2022]
Abstract
Previously, we demonstrated that outward currents activated by calcium-induced calcium release (CICR) opposed depolarization-induced action potential (AP) generation in dissociated mudpuppy parasympathetic neurons [J Neurophysiol 88 (2002) 1119]. In the present study, we tested whether AP generation by depolarizing current ramps could be altered by dissipating the mitochondrial membrane potential and thus interrupting mitochondrial Ca2+ buffering. Exposure to the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP; 2 microM) alone or in combination with the mitochondrial ATP synthase inhibitor oligomycin (8 microg/ml), increased the latency to AP generation. Exposure to the electron transport chain inhibitor rotenone (10 microM) alone or in combination with oligomycin (8 microg/ml) similarly increased the latency to AP generation. CCCP and oligomycin or rotenone and oligomycin treatment caused rhodamine 123 loss from mitochondria within a few minutes, confirming that the mitochondrial membrane potential was dissipated during drug exposure. Oligomycin alone had no effect on the latency to AP generation and did not cause loss of rhodamine 123 from mitochondria. The increase in latency induced by CCCP and oligomycin was similar when recordings were made with either the perforated patch or standard whole cell patch recording configuration. Exposure to the endoplasmic reticulum Ca-ATPase inhibitor thapsigargin (1 microM), decreased the latency to AP generation. In cells pretreated with thapsigargin to eliminate CICR, CCCP and oligomycin had no effect on AP latency. Pretreatment with iberiotoxin (IBX; 100 nM), an inhibitor of large conductance, calcium- and voltage-activated potassium channels, reduced the extent of the CCCP- and oligomycin-induced increase in latency to AP generation. These results indicate that treatment with CCCP or rotenone to dissipate the mitochondrial membrane potential, a condition which should minimize sequestration of Ca2+ by mitochondria, facilitated the Ca(2+)-induced Ca2+ release activation of IBX-sensitive and IBX-insensitive conductances that regulate AP generation.
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Affiliation(s)
- K L Barstow
- Department of Anatomy and Neurobiology, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
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Parsons RL, Barstow KL, Scornik FS. Spontaneous miniature hyperpolarizations affect threshold for action potential generation in mudpuppy cardiac neurons. J Neurophysiol 2002; 88:1119-27. [PMID: 12205133 DOI: 10.1152/jn.2002.88.3.1119] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mudpuppy parasympathetic neurons exhibit spontaneous miniature hyperpolarizations (SMHs) that are generated by potassium currents, which are spontaneous miniature outward currents (SMOCs), flowing through clusters of large conductance voltage- and calcium (Ca(2+))-activated potassium (BK) channels. The underlying SMOCs are initiated by a Ca(2+)-induced Ca(2+) release (CICR) mechanism. Perforated-patch whole cell voltage recordings were used to determine whether activation of SMHs contributed to action potential (AP) repolarization or affected the latency to AP generation. Blockade of BK channels by iberiotoxin (IBX, 100 nM) slowed AP repolarization and increased AP duration. Treatment with omega-conotoxin GVIA (3 microM) or nifedipine (10 microM) to inhibit Ca(2+) influx through N- or L-type voltage-dependent calcium channels (VDCCs), respectively, also decreased the rate of AP repolarization and increased AP duration. Elimination of CICR by treatment with either thapsigargin (1 microM) or ryanodine (10 microM) produced no significant change in AP repolarization or duration. Blockade of BK channels with IBX and inhibition of N-type VDCCs with omega-conotoxin GVIA, but not inhibition of L-type VDCCs with nifedipine, decreased the latency of AP generation. A decrease in latency to AP generation occurred with elimination of SMHs by inhibition of CICR following treatment with thapsigargin. Ryanodine treatment decreased AP latency in three of six cells. Apamin (100 nM) had no affect on AP repolarization, duration, or latency to AP generation, but did decrease the hyperpolarizing afterpotential (HAP). Inhibition of L-type VDCCs by nifedipine also decreased HAP amplitude. Inhibition of CICR by either thapsigargin or ryanodine treatment increased the number of APs generated with long depolarizing current pulses, whereas exposure to IBX or omega-conotoxin GVIA depressed excitability. We conclude that CICR, the process responsible for SMH generation, represents a unique mechanism to modulate the response to subthreshold depolarizing currents that drive the membrane potential toward the threshold for AP initiation but does not contribute to AP repolarization. Subthreshold depolarizations would not activate sufficient numbers of VDCCs to allow Ca(2+) influx to elevate [Ca(2+)](i) to the extent needed to directly activate nearby BK channels. However, the elevation in [Ca(2+)](i) is sufficient to trigger CICR from ryanodine-sensitive Ca(2+) stores. Thus CICR acts as an amplification mechanism to trigger a local elevation of [Ca(2+)](i) near a cluster of BK channels to activate these channels at negative levels of membrane potential.
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Affiliation(s)
- Rodney L Parsons
- Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA.
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12
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Mitra P, Slaughter MM. Mechanism of generation of spontaneous miniature outward currents (SMOCs) in retinal amacrine cells. J Gen Physiol 2002; 119:355-72. [PMID: 11929886 PMCID: PMC2311394 DOI: 10.1085/jgp.20028478] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A subtype of retinal amacrine cells displayed a distinctive array of K(+) currents. Spontaneous miniature outward currents (SMOCs) were observed in the narrow voltage range of -60 to -40 mV. Depolarizations above approximately -40 mV were associated with the disappearance of SMOCs and the appearance of transient (I(to)) and sustained (I(so)) outward K(+) currents. I(to) appeared at about -40 mV and its apparent magnitude was biphasic with voltage, whereas I(so) appeared near -30 mV and increased linearly. SMOCs, I(to), and a component of I(so) were Ca(2+) dependent. SMOCs were spike shaped, occurred randomly, and had decay times appreciably longer than the time to peak. In the presence of cadmium or cobalt, SMOCs with pharmacologic properties identical to those seen in normal Ringer's could be generated at voltages of -20 mV and above. Their mean amplitude was Nernstian with respect to [K(+)](ext) and they were blocked by tetraethylammonium. SMOCs were inhibited by iberiotoxin, were insensitive to apamin, and eliminated by nominally Ca(2+)-free solutions, indicative of BK-type Ca(2+)-activated K(+) currents. Dihydropyridine Ca(2+) channel antagonists and agonists decreased and increased SMOC frequencies, respectively. Ca(2+) permeation through the kainic acid receptor had no effect. Blockade of organelle Ca(2+) channels by ryanodine, or intracellular Ca(2+) store depletion with caffeine, eradicated SMOCs. Internal Ca(2+) chelation with 10 mM BAPTA eliminated SMOCs, whereas 10 mM EGTA had no effect. These results suggest a mechanism whereby Ca(2+) influx through L-type Ca(2+) channels and its subsequent amplification by Ca(2+)-induced Ca(2+) release via the ryanodine receptor leads to a localized elevation of internal Ca(2+). This amplified Ca(2+) signal in turn activates BK channels in a discontinuous fashion, resulting in randomly occurring SMOCs.
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Affiliation(s)
- Pratip Mitra
- Department of Physiology and Biophysics, School of Medicine, State University of New York at Buffalo, Buffalo, NY 14214, USA
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Mitra P, Slaughter MM. Calcium-induced transitions between the spontaneous miniature outward and the transient outward currents in retinal amacrine cells. J Gen Physiol 2002; 119:373-88. [PMID: 11929887 PMCID: PMC2311395 DOI: 10.1085/jgp.20028479] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Spontaneous miniature outward currents (SMOCs) occur in a subset of retinal amacrine cells at membrane potentials between -60 and -40 mV. At more depolarized potentials, a transient outward current (I(to)) appears and SMOCs disappear. Both SMOCs and the I(to) are K(+) currents carried by BK channels. They both arise from Ca(2+) influx through high voltage-activated (HVA) Ca(2+) channels, which stimulates release of internal Ca(2+) from caffeine- and ryanodine-sensitive stores. An increase in Ca(2+) influx resulted in an increase in SMOC frequency, but also led to a decline in SMOC mean amplitude. This reduction showed a temporal dependence: the effect being greater in the latter part of a voltage step. Thus, Ca(2+) influx, although required to generate SMOCs, also produced a negative modulation of their amplitudes. Increasing Ca(2+) influx also led to a decline in the first latency to SMOC occurrence. A combination of these effects resulted in the disappearance of SMOCs, along with the concomitant appearance of the I(to) at high levels of Ca(2+) influx. Therefore, low levels of Ca(2+) influx, arising from low levels of activation of the HVA Ca(2+) channels, produce randomly occurring SMOCs within the range of -60 to -40 mV. Further depolarization leads to greater activation of the HVA Ca(2+) channels, larger Ca(2+) influx, and the disappearance of discontinuous SMOCs, along with the appearance of the I(to). Based on their characteristics, SMOCs in retinal neurons may function as synaptic noise suppressors at quiescent glutamatergic synapses.
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Affiliation(s)
- Pratip Mitra
- Department of Physiology and Biophysics, School of Medicine, State University of New York at Buffalo, Buffalo, NY 14214, USA
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Shirasaki T, Houtani T, Sugimoto T, Matsuda H. Spontaneous transient outward currents: modulation by nociceptin in murine dentate gyrus granule cells. Brain Res 2001; 917:191-205. [PMID: 11640905 DOI: 10.1016/s0006-8993(01)02916-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Spontaneous transient outward currents have been found in peripheral neurons and smooth muscle cells, but rarely in central neurons. Using a nystatin-perforated patch clamp technique, we succeeded in recording spontaneous transient outward currents in mouse dentate gyrus granule cells. Nociceptin/orphanin FQ increased the amplitude and frequency of transient outward currents. We consider modulation of spontaneous transient outward currents to be a new means to regulate cell activity in central neurons, and studied their characteristics and mechanism of augmentation. The whole-cell current-voltage relationship showed outward rectification and the reversal potential was close to the equilibrium potential for K+. The frequency of spontaneous transient outward currents increased at depolarized potentials. Tetraethylammonium, iberiotoxin and a Ca2+ chelator BAPTA-AM inhibited spontaneous transient outward currents. These results suggest the involvement of large-conductance Ca2+-activated K+ channels. Single-channel recordings in the inside-out configuration revealed Ca2+-activated K+ channels with a conductance ranging from 82 to 352 pS. The augmenting effect of nociceptin/orphanin FQ was cancelled by [Phe1psi(CH2-NH)Gly2]Nociceptin(1-13)NH2. Cd2+ did not affect the transient outward currents or augmentation by nociceptin/orphanin FQ. Whereas nociceptin/orphanin FQ, theophylline and cyclic ADP ribose induced transient outward currents with short duration observed under control conditions, inositol 1,4,5-trisphosphate induced transient outward currents with long duration, in addition to those with short duration. Ryanodine inhibited nociceptin/orphanin FQ from augmenting spontaneous transient outward currents. Our data suggest that Ca2+ sparks transiently activate large-conductance Ca2+-activated K+ channels to induce transient outward currents. Nociceptin/orphanin FQ probably sensitizes ryanodine receptors and increases transient outward currents to reduce cell excitability.
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Affiliation(s)
- T Shirasaki
- Department of Physiology, Kansai Medical University, Moriguchi, 570-8506, Osaka, Japan
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15
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Meldolesi J. Rapidly exchanging Ca2+ stores in neurons: molecular, structural and functional properties. Prog Neurobiol 2001; 65:309-38. [PMID: 11473791 DOI: 10.1016/s0301-0082(01)00004-1] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- J Meldolesi
- DIBIT, Scientific Institute S. Raffaele, Vita-Salute University, Via Olgettina, 58, 20132, Milan, Italy.
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16
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Arima J, Matsumoto N, Kishimoto K, Akaike N. Spontaneous miniature outward currents in mechanically dissociated rat Meynert neurons. J Physiol 2001; 534:99-107. [PMID: 11432995 PMCID: PMC2278683 DOI: 10.1111/j.1469-7793.2001.00099.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
1. Spontaneous miniature outward currents (SMOCs) were observed in mechanically dissociated rat Meynert neurons using nystatin perforated patch recordings under voltage-clamp conditions. 2. SMOCs were blocked by apamin, a selective blocker of small conductance Ca(2+)-activated K(+) (SK) channels, but not by blockers for other types of Ca(2+)-activated K(+) channel. 3. Ryanodine (10-100 microM) reduced both the amplitude and frequency of SMOCs. Caffeine (1 mM) increased the SMOC frequency. Blockers of the sarco/endoplasmic reticulum Ca(2+)-ATPase completely abolished SMOCs, indicating a requirement for functioning sarco/endoplasmic reticulum (SR/ER) Ca(2+) stores. 4. Both Cd(2+)-containing and Ca(2+)-free solutions partially inhibited SMOC frequency, a result which suggests that Ca(2+) influx contributes to, but is not essential for, SMOC generation. 5. Thus, SMOCs are SK currents linked to ryanodine- and caffeine-sensitive SR/ER Ca(2+) stores, and are only indirectly influenced by extracellular Ca(2+) influx. The development of this new, minimally invasive mechanical dissociation method has revealed that SMOCs are common in native CNS neurons.
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Affiliation(s)
- J Arima
- Cellular and System Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
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17
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Scornik FS, Merriam LA, Parsons RL. Number of K(Ca) channels underlying spontaneous miniature outward currents (SMOCs) in mudpuppy cardiac neurons. J Neurophysiol 2001; 85:54-60. [PMID: 11152705 DOI: 10.1152/jn.2001.85.1.54] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous miniature outward currents (SMOCs) in parasympathetic neurons from mudpuppy cardiac ganglia are caused by activation of TEA- and iberiotoxin-sensitive, Ca(2+)-dependent K(+) (BK) channels. Previously we reported that SMOCs are activated by Ca(2+)-induced Ca(2+) release (CICR) from caffeine- and ryanodine-sensitive intracellular Ca(2+) stores. In the present study, we analyzed the single channel currents that contribute to SMOC generation in mudpuppy cardiac neurons. The slope conductance of BK channels, determined from the I-V relationship of single-channel currents recorded with cell-attached patches in physiological K(+) concentrations, was 84 pS. The evidence supporting the identity of this channel as the channel involved in SMOC generation was its sensitivity to internal Ca(2+), external TEA, and caffeine. In cell-attached patch recordings, 166 microM TEA applied in the pipette reduced single-channel current amplitude by 32%, and bath-applied caffeine increased BK channel activity. The ratio between the averaged SMOC amplitude and the single-channel current amplitude was used to estimate the average number of channels involved in SMOC generation. The estimated number of channels involved in generation of an averaged SMOC ranged from 18 to 23 channels. We also determined that the Po of the BK channels at the peak of a SMOC remains constant at voltages more positive than -20 mV, suggesting that the transient rise in intracellular Ca(2+) from ryanodine-sensitive intracellular stores in the vicinity of the BK channel reached concentrations most likely exceeding 40 microM.
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Affiliation(s)
- F S Scornik
- Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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18
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Akita T, Kuba K. Functional triads consisting of ryanodine receptors, Ca(2+) channels, and Ca(2+)-activated K(+) channels in bullfrog sympathetic neurons. Plastic modulation of action potential. J Gen Physiol 2000; 116:697-720. [PMID: 11055998 PMCID: PMC2229477 DOI: 10.1085/jgp.116.5.697] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Fluorescent ryanodine revealed the distribution of ryanodine receptors in the submembrane cytoplasm (less than a few micrometers) of cultured bullfrog sympathetic ganglion cells. Rises in cytosolic Ca(2+) ([Ca(2+)](i)) elicited by single or repetitive action potentials (APs) propagated at a high speed (150 microm/s) in constant amplitude and rate of rise in the cytoplasm bearing ryanodine receptors, and then in the slower, waning manner in the deeper region. Ryanodine (10 microM), a ryanodine receptor blocker (and/or a half opener), or thapsigargin (1-2 microM), a Ca(2+)-pump blocker, or omega-conotoxin GVIA (omega-CgTx, 1 microM), a N-type Ca(2+) channel blocker, blocked the fast propagation, but did not affect the slower spread. Ca(2+) entry thus triggered the regenerative activation of Ca(2+)-induced Ca(2+) release (CICR) in the submembrane region, followed by buffered Ca(2+) diffusion in the deeper cytoplasm. Computer simulation assuming Ca(2+) release in the submembrane region reproduced the Ca(2+) dynamics. Ryanodine or thapsigargin decreased the rate of spike repolarization of an AP to 80%, but not in the presence of iberiotoxin (IbTx, 100 nM), a BK-type Ca(2+)-activated K(+) channel blocker, or omega-CgTx, both of which decreased the rate to 50%. The spike repolarization rate and the amplitude of a single AP-induced rise in [Ca(2+)](i) gradually decreased to a plateau during repetition of APs at 50 Hz, but reduced less in the presence of ryanodine or thapsigargin. The amplitude of each of the [Ca(2+)](i) rise correlated well with the reduction in the IbTx-sensitive component of spike repolarization. The apamin-sensitive SK-type Ca(2+)-activated K(+) current, underlying the afterhyperpolarization of APs, increased during repetitive APs, decayed faster than the accompanying rise in [Ca(2+)](i), and was suppressed by CICR blockers. Thus, ryanodine receptors form a functional triad with N-type Ca(2+) channels and BK channels, and a loose coupling with SK channels in bullfrog sympathetic neurons, plastically modulating AP.
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Affiliation(s)
- Tenpei Akita
- Department of Physiology, Nagoya University School of Medicine, Nagoya 466-8550, Japan
| | - Kenji Kuba
- Department of Physiology, Nagoya University School of Medicine, Nagoya 466-8550, Japan
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19
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Merriam LA, Scornik FS, Parsons RL. Ca(2+)-induced Ca(2+) release activates spontaneous miniature outward currents (SMOCs) in parasympathetic cardiac neurons. J Neurophysiol 1999; 82:540-50. [PMID: 10444654 DOI: 10.1152/jn.1999.82.2.540] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mudpuppy parasympathetic cardiac neurons exhibit spontaneous miniature outward currents (SMOCs) that are thought to be due to the activation of clusters of large conductance Ca(2+)-activated K(+) channels (BK channels) by localized release of Ca(2+) from internal stores close to the plasma membrane. Perforated-patch whole cell recordings were used to determine whether Ca(2+)-induced Ca(2+) release (CICR) is involved in SMOC generation. We confirmed that BK channels are involved by showing that SMOCs are inhibited by 100 nM iberiotoxin or 500 microM tetraethylammonium (TEA), but not by 100 nM apamin. SMOC frequency is decreased in solutions that contain 0 Ca(2+)/3.6 mM Mg(2+), and also in the presence of 1 microM nifedipine and 3 microM omega-conotoxin GVIA, suggesting that SMOC activation is dependent on calcium influx. However, Ca(2+) influx alone is not sufficient; SMOC activation is also dependent on Ca(2+) release from the caffeine- and ryanodine-sensitive Ca(2+) store, because exposure to 2 mM caffeine consistently caused an increase in SMOC frequency, and 10-100 microM ryanodine altered the configuration of SMOCs and eventually inhibited SMOC activity. Depletion of intracellular Ca(2+) stores by the Ca-ATPase inhibitor cyclopiazonic acid (10 microM) inhibited SMOC activity, even when Ca(2+) influx was not compromised. We also tested the effects of the membrane-permeable Ca(2+) chelators, bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid-AM (BAPTA-AM) and EGTA-AM. EGTA-AM (10 microM) caused no inhibition of SMOC activation, whereas 10 microM BAPTA-AM consistently inhibited SMOCs. After SMOCs were completely inhibited by BAPTA, 3 mM caffeine caused SMOC activity to resume. This effect was reversible on removal of caffeine and suggests that the source of Ca(2+) that triggers the internal Ca(2+) release channel is different from the source of Ca(2+) that activates clusters of BK channels. We propose that influx of Ca(2+) through voltage-dependent Ca(2+) channels is required for SMOC generation, but that the influx of Ca(2+) triggers CICR from intracellular stores, which then activates the BK channels responsible for SMOC generation.
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Affiliation(s)
- L A Merriam
- Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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20
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Koizumi S, Bootman MD, Bobanović LK, Schell MJ, Berridge MJ, Lipp P. Characterization of elementary Ca2+ release signals in NGF-differentiated PC12 cells and hippocampal neurons. Neuron 1999; 22:125-37. [PMID: 10027295 DOI: 10.1016/s0896-6273(00)80684-4] [Citation(s) in RCA: 131] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Elementary Ca2+ release signals in nerve growth factor- (NGF-) differentiated PC12 cells and hippocampal neurons, functionally analogous to the "Ca2+ sparks" and "Ca2+ puffs" identified in other cell types, were characterized by confocal microscopy. They either occurred spontaneously or could be activated by caffeine and metabotropic agonists. The release events were dissimilar to the sparks and puffs described so far, as many arose from clusters of both ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (InsP3Rs). Increasing either the stimulus strength or loading of the intracellular stores enhanced the frequency of and coupling between elementary release sites and evoked global Ca2+ signals. In the PC12 cells, the elementary Ca2+ release preferentially occurred around the branch points. Spatio-temporal recruitment of such elementary release events may regulate neuronal activities.
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Affiliation(s)
- S Koizumi
- Laboratory of Molecular Signalling, The Babraham Institute, Cambridge, United Kingdom
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21
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Seutin V, Massotte L, Scuvée-Moreau J, Dresse A. Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats. J Neurophysiol 1998; 80:3361-4. [PMID: 9862933 DOI: 10.1152/jn.1998.80.6.3361] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats. J. Neurophysiol. 80: 3361-3364, 1998. Intracellular recordings from substantia nigra slices revealed the existence of spontaneous hyperpolarizations (amplitude 2-8 mV, duration 100-400 ms) at -60 mV in most dopaminergic neurons of neonatal (9-15 days) but not adult rats. These events were blocked by apamin (300 nM) and bicuculline methochloride (100-300 microM), which blocks apamin-sensitive currents. They were unaffected by the selective gamma-aminobutyric acid-A (GABAA) antagonists SR95531 (100 microM) and picrotoxin (30-50 microM), the GABAB antagonist CGP35348 (300 microM), the D2 antagonist haloperidol (1 microM), and the metabotropic antagonist MCPG (1 mM). The hyperpolarizations were strongly attenuated or abolished when recording electrodes contained 200 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. They were resistant to tetrodotoxin in the majority of the cells. They had some voltage dependency and were in some cases transiently potentiated when cells were briefly depolarized by current injection. We conclude that dopaminergic neurons have developmentally regulated physiological properties. These spontaneous hyperpolarizations might affect the firing rate of these cells, which was found to be lower in neonates than in adults.
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Affiliation(s)
- V Seutin
- Laboratory of Pharmacology, University of Liège, B-4000 Sart Tilman par Liège 1, Belgium
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22
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Affiliation(s)
- M J Berridge
- The Babraham Institute, Babraham Laboratory of Molecular Signalling, Cambridge, United Kingdom
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23
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Marrion NV, Adams PR, Gruner W. Multiple kinetic states underlying macroscopic M-currents in bullfrog sympathetic neurons. Proc Biol Sci 1997; 248:207-14. [PMID: 1354358 DOI: 10.1098/rspb.1992.0063] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
M-current is a time- and voltage-dependent potassium current which is suppressible by muscarinic receptor activation. We have used curve fitting and noise analysis to determine if macroscopic M-currents deviate from a previously predicted simple two-state kinetic scheme. The M-current was best described by three kinetically distinct components: 'fast' (tau 0), 'intermediate' (tau 1) and 'slow' (tau 2) time constants. The 'fast' (tau 0) and 'intermediate' (tau 1) components were identified from the spectra of M-current noise at potentials positive to the cells' resting membrane potential. The 'intermediate' (tau 1) and 'slow' (tau 2) components were seen by curve fitting M-current deactivation currents. The 'intermediate' (tau 1) time constant was voltage dependent (decreasing e-fold in 23 mV), but voltage dependence of the 'fast' (tau 0) and 'slow' (tau 2) components was not obvious. All kinetic components were sensitive to muscarine, with the 'intermediate' (tau 1) and 'slow' (tau 2) being equally so. These data suggest that all components may derive from the same channel population, and that the M-channel may have at least four kinetic states.
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Affiliation(s)
- N V Marrion
- Howard Hughes Medical Institute, Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794
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24
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Affiliation(s)
- D A Eisner
- Department of Veterinary Preclinical Sciences, University of Liverpool, UK
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25
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Affiliation(s)
- M D Bootman
- Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, UK.
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26
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Lipp P, Niggli E. A hierarchical concept of cellular and subcellular Ca(2+)-signalling. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1996; 65:265-96. [PMID: 9062435 DOI: 10.1016/s0079-6107(96)00014-4] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- P Lipp
- Department of Physiology, University of Bern, Switzerland
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27
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Affiliation(s)
- M J Berridge
- Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, U.K
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28
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Usachev Y, Kostyuk P, Verkhratsky A. 3-Isobutyl-1-methylxanthine (IBMX) affects potassium permeability in rat sensory neurones via pathways that are sensitive and insensitive to [Ca2+]in. Pflugers Arch 1995; 430:420-8. [PMID: 7491267 DOI: 10.1007/bf00373918] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effects of externally applied 3-isobutyl-1-methylxanthine (IBMX), in millimolar concentrations, on the membrane currents in dorsal root ganglia (DRG) neurones isolated from newborn rats were investigated using the amphotericin-based "perforated" patch-clamp technique. In some experiments, simultaneous measurements of intracellular Ca2+ concentration ([Ca2+]in) were performed using fura-2 microfluorimetry. Applications of IBMX induced elevation of [Ca2+]in resulting from Ca2+ release from caffeine-ryanodine-sensitive internal stores. In addition to Ca2+ release, IBMX produced a biphasic membrane current response comprised of an inward current transiently interrupted by outward current. The onset of the inward current slightly preceded the onset of the [Ca2+]in transient, while the interrupting outward current developed synchronously with the [Ca2+]in rise. The development of IBMX-induced outward current ultimately needed the [Ca2+]in elevation. After the depletion of Ca2+ stores by IBMX or caffeine exposure, the subsequent IBMX challenge failed to produce both the [Ca2+]in transient and outward membrane current, although the inward current remained unchanged. Both components of the IBMX-induced membrane current response had a reversal potential close to the K+ equilibrium potential and the IBMX-induced membrane current response disappeared while dialysing the cell interior with K(+)-free, Cs(+)-containing solutions suggesting their association with K+ channel activity. External administration of 10 mM tetraethylammonium chloride (TEA-Cl) evoked an inward current similar to that observed in response to IBMX; in the presence of TEA-Cl, IBMX application was almost unable to induce additional inward current. IBMX (5 mM) effectively (approximately 50%) inhibited K+ currents evoked by step depolarizations of membrane potential.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- Y Usachev
- Department of General Physiology of the Nervous System, Bogomoletz Institute of Physiology, Kiev, Ukraine
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29
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Chen H, Jassar BS, Kurenny DE, Smith PA. Phorbol ester-induced M-current suppression in bull-frog sympathetic ganglion cells: insensitivity to kinase inhibitors. Br J Pharmacol 1994; 113:55-62. [PMID: 7812633 PMCID: PMC1510084 DOI: 10.1111/j.1476-5381.1994.tb16173.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
1. The effects of 1-oleoyl-2-acetyl-sn-glycerol (OAG), phorbol 12-myristate 13-acetate (PMA), 4-alpha-phorbol and muscarine on B-neurones from bull-frog sympathetic ganglion were studied by means of whole-cell patch-clamp recording. With the exception of 4-alpha-phorbol, all of these agonists reduced the steady-state outward current recorded at -30 mV as a result of suppression of a voltage-dependent, non-inactivating K(+)-current, the M-current, (IM). 2. Of the cells tested, 34% displayed bona fide responses to OAG (20 microM). The chance of recording a response was not decreased when the protein kinase inhibitor, 1-(5-isoquinolinylsulphonyl)-2-methyl-piperazine (H-7; 50 or 75 microM) was included simultaneously in the extracellular solution and in the pipette solution. 3. The presence of 50 microM H-7 on both sides of the membrane or 500 nM staurosporine in the pipette solution did not prevent responses to brief (1-2 min) or prolonged (> 20 min) applications of PMA. 4. Brief (1-2 min) extracellular application of H-7 (300 microM) suppressed IM by about 29%. 5. The most likely explanation of these data is that PMA and OAG modulate IM via a mechanism that is independent of protein kinase C (PKC). The availability of such a mechanism poses new questions as to the mechanism of muscarine-induced IM suppression.
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Affiliation(s)
- H Chen
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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30
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Affiliation(s)
- P A Smith
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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31
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Marrion NV. M-current suppression by agonist and phorbol ester in bullfrog sympathetic neurons. Pflugers Arch 1994; 426:296-303. [PMID: 8183640 DOI: 10.1007/bf00374785] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Activation of protein kinase C (PKC) by phorbol esters is known to suppress M-current. 4-beta-Phorbol 12,13-dibutyrate (PDBu) irreversibly suppressed M-current in a concentration-dependent manner (Ki 38 nM). Inhibitors of PKC, the pseudo-substrate peptide PKCI (19-31), staurosporine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) antagonized PDBu-mediated suppression of M-current. Suppression of M-current by muscarine and luteinizing hormone-releasing hormone (LHRH) was unaffected by PKCI (19-31) and H7, but was antagonized by staurosporine. The balance of data suggests that suppression of M-current by agonists is probably not mediated by activation of PKC. Addition and subsequent removal of PDBu to M-current suppressed by muscarine prevented the action of PDBu, while closing M-channels by voltage or blocking by barium did not. This suggests that M-channel closure by muscarine protects those channels from the effects of PDBu. Partial suppression of M-current by low concentrations of muscarine antagonized the response to PDBu, with the magnitude of suppression equivalent to that seen with PDBu alone. It is suggested that two interconvertable populations of M-channels exist, one that is sensitive to both agonist and PDBu and another that can only be suppressed by agonist.
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Affiliation(s)
- N V Marrion
- Howard Hughes Medical Institute, SUNY at Stony Brook 11794
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32
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Munakata M, Akaike N. Theophylline affects three different potassium currents in dissociated rat cortical neurones. J Physiol 1993; 471:599-616. [PMID: 8120824 PMCID: PMC1143979 DOI: 10.1113/jphysiol.1993.sp019918] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
1. The effects of theophylline in pyramidal neurones acutely dissociated from the rat frontal cortex were investigated in the whole-cell configuration, using the nystatin-perforated patch-clamp technique. 2. Ten millimolar theophylline evoked triphasic responses: a small slow outward current (Iso), then a large transient outward current (Ito) and finally a slow sustained inward current (Isi). The reversal potentials of the three current components shifted 56-58 mV for a 10-fold change in extracellular K+ concentration, thereby indicating that all these current components were predominantly carried by K+. 3. Iso had no voltage dependence, whereas Ito showed a steep outward rectification. Iso was relatively resistant to tetraethylammonium (TEA) with an IC50 of 10 mM. Ito was susceptible to submillimolar TEA with an IC50 of 0.8 mM. 4. Isi was a net inward current mainly resulting from suppression of the M-current (IM). 5. These three current components had a distinct concentration dependence; in particular, Isi was evoked at a relatively lower concentration range. 6. Ito was not observed when the intracellular Ca2+ was chelated by 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) of 10 mM, using the conventional whole-cell recording configuration, whereas both Iso and Isi were retained but gradually diminished. 7. In Ca(2+)-free external solution, these responses were fully elicited by the first application of theophylline. However, Ito disappeared during successive applications and Iso, but not Isi, also decreased. Similar results were obtained in the presence of ryanodine. 8. Theophylline apparently affects three different kinds of K+ currents in rat cortical neurones. Both Iso and Ito depend on internal calcium mobilized from an intracellular Ca2+ store by theophylline, while Isi was not primarily mediated by a change in [Ca2+]i.
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Affiliation(s)
- M Munakata
- Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan
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33
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Fletcher GH, Chiappinelli VA. The actions of the kappa 1 opioid agonist U-50,488 on presynaptic nerve terminals of the chick ciliary ganglion. Neuroscience 1993; 53:239-50. [PMID: 8385747 DOI: 10.1016/0306-4522(93)90302-v] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The actions of the kappa 1 opioid receptor agonist U-50,488 (trans-(+-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benz ene - acetamide methane sulfonate) on the membrane properties of presynaptic calyciform nerve terminals of the chick ciliary ganglion were examined using intracellular recordings obtained from intact ganglion preparations maintained in vitro. U-50,488 produced a concentration-dependent (30-1000 microM) hyperpolarization with an apparent increase in input resistance. This hyperpolarization resulted from inhibition of the Na(+)-K+ inward rectifier, since it was blocked by 3 mM Cs+ and was not observed when terminals were depolarized beyond resting potential where inward rectification was voltage inactivated. A depolarizing effect on membrane potential with a further rise in input resistance was commonly observed at the highest perfused U-50,488 concentration (1 mM). The depolarizing event appears to result from a decrease in membrane potassium conductance, as the reversal potential for the response was estimated to be between -70 and -90 mV and the potassium channel blocker Ba2+ (1 mM) abolished the response. The kappa 1 opioid receptor agonist also blocked spontaneously occurring miniature hyperpolarizations in the terminals, which are considered to be due to a Ca(2+)-dependent K+ conductance. Most of the responses to U-50,488 were abolished in the presence of the kappa 1 receptor antagonist norbinaltorphimine. In conclusion, the excitability of presynaptic nerve terminals in the chick ciliary ganglion can be modulated by the inhibition of at least three separate ion conductances following activation of kappa 1 opioid receptor sites in the nerve terminal region.
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Affiliation(s)
- G H Fletcher
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, MO 63104
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Fletcher GH, Chiappinelli VA. Spontaneous miniature hyperpolarizations of presynaptic nerve terminals in the chick ciliary ganglion. Brain Res 1992; 579:165-8. [PMID: 1623403 DOI: 10.1016/0006-8993(92)90757-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Intracellular recordings from presynaptic nerve terminals in the chick ciliary ganglion revealed the presence of spontaneous miniature hyperpolarizations in virtually all (approximately 86%) nerve terminals examined. These spontaneous events appeared as small, brief hyperpolarizations at resting potential and were observed to increase or decrease as the membrane potential was depolarized or hyperpolarized from rest, respectively. The hyperpolarizing potentials were sensitive to blockade by tetraethylammonium and Ba2+, while caffeine increased then abolished these events. The voltage fluctuations were unaffected by tetrodotoxin, low Ca2+ external solution or the synaptic blockers, picrotoxin and strychnine. These spontaneous, transient, miniature hyperpolarizations may be due to the brief and co-ordinated activation of between 15-60 Ca(2+)-dependent K+ channels following the release of Ca2+ from internal stores.
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Affiliation(s)
- G H Fletcher
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, MO 63104
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Marrion NV, Adams PR. Release of intracellular calcium and modulation of membrane currents by caffeine in bull-frog sympathetic neurones. J Physiol 1992; 445:515-35. [PMID: 1380086 PMCID: PMC1179995 DOI: 10.1113/jphysiol.1992.sp018937] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
1. Calcium release and sequestration were studied in whole-cell voltage-clamped bull-frog sympathetic neurones by image analysis of Fura-2 signals. 2. Application of caffeine (10 mM) to cells voltage clamped at -38 mV caused a rapid increase in intracellular calcium concentration ([Ca2+]i) to a mean value of 352 +/- 33 nM, which activated an outward current. In the continued presence of caffeine the rise in [Ca2+]i slowly declined to a sustained plateau of 196 +/- 20 nM (112 nM above control levels), while the outward current rapidly decayed. Peak calcium release was highest at the edge of the cell. 3. The caffeine-evoked intracellular calcium increase was reduced by two inhibitors of calcium-induced calcium release, ryanodine and procaine. The residual non-suppressible increase in [Ca2+]i may indicate that caffeine can release calcium from two pharmacologically distinct intracellular stores. 4. Inhibition of the caffeine-evoked release of calcium by ryanodine was both concentration and 'use dependent' so that the full inhibitory effect was only observed when caffeine was applied for the second time in the presence of ryanodine. In contrast, the action of procaine did not show any 'use dependence' and unlike ryanodine was fully reversible. 5. The outward current was sensitive to blockers of the large conductance calcium-activated potassium current, Ic. Analysis of variance from this current indicated that it arose at least partly from summation of spontaneous miniature outward currents. 6. The magnitude and duration of calcium release by caffeine was dependent on the resting level of intracellular calcium and the caffeine exposure time. This, together with the pharmacology of the release, suggests that caffeine increases intracellular calcium by sensitizing calcium-induced calcium release. 7. The evoked [Ca2+]i increase was enhanced in amplitude by intracellular application of Ruthenium Red. This effect was mimicked by extracellular application of the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (FCCP) but not by internal application of FCCP or other inhibitors of mitochondrial Ca2+ uptake. This suggests that the evoked increase in [Ca2+]i is predominantly buffered by a Ruthenium Red-sensitive sequestration process which is not mitochondrial.
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Affiliation(s)
- N V Marrion
- Howard Hughes Medical Institute, Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794
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Parsons RL, Konopka LM. Analysis of the galanin-induced decrease in membrane excitability in mudpuppy parasympathetic neurons. Neuroscience 1991; 43:647-60. [PMID: 1717889 DOI: 10.1016/0306-4522(91)90323-g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Previously, we showed that the neuropeptide galanin hyperpolarizes and decreases membrane excitability of mudpuppy parasympathetic neurons [Konopka L. M., McKeon T. W. and Parsons R. L. (1989) J. Physiol. 410, 107-122]. We also demonstrated that membrane excitability remains depressed when the agonist-induced potential change is negated electrotonically. We hypothesized that galanin inhibits the membrane conductances associated with spike generation. However, we cannot rule out the possibility that the decreased excitability is due to a galanin-induced increase in membrane potassium conductance which reduces the effectiveness of subsequent depolarizing stimuli. Therefore, in the present study we tested, with the galanin-induced hyperpolarization negated, whether the galanin-induced increased membrane potassium conductance was responsible for the decreased excitability. The results showed that the galanin-induced decreased excitability was not dependent on the peak amplitude of the galanin-induced hyperpolarization. Furthermore, the decreased excitability occurred in cells in which there was no measurable galanin-induced hyperpolarization. Moreover, in most cells the galanin-induced decrease in input resistance, measured at the peak of the hyperpolarization (3-25 mV), was less than 15% and when the hyperpolarization was negated electronically, the decrease was even less (approximately 2%). These results indicated that when the hyperpolarization was negated, the galanin-induced increase in potassium conductance was not responsible for the decreased excitability. In preparations pretreated with 5 mM tetraethylammonium, galanin decreased excitability which indicated that a galanin-induced decrease in the calcium-dependent potassium current was not necessary for the decreased excitability. Galanin also decreased excitability in preparations exposed to either 1-3 microM tetrodotoxin or 100-200 microM cadmium. Following galanin application, the threshold for initiation of tetrodotoxin-insensitive spikes was shifted to more positive membrane potentials. Galanin also decreased the amplitude and hyperpolarizing afterpotential of barium spikes in the absence of any agonist-induced hyperpolarization. These observations confirmed that galanin decreased the voltage-dependent calcium conductance. In the present study, we showed that when the hyperpolarization was negated, galanin decreased excitability by shifting the threshold for spike generation regardless of whether voltage-dependent sodium or calcium currents were primarily responsible for the depolarizing component of the action potential.
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Affiliation(s)
- R L Parsons
- Department of Anatomy and Neurobiology, College of Medicine, University of Vermont, Burlington 05405
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Sims SM, Clapp LH, Walsh JV, Singer JJ. Dual regulation of M current in gastric smooth muscle cells: beta-adrenergic-muscarinic antagonism. Pflugers Arch 1990; 417:291-302. [PMID: 2177185 DOI: 10.1007/bf00370995] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The effects of the beta-adrenergic agent isoproterenol on membrane currents were studied in freshly dissociated gastric smooth muscle cells of Bufo marinus. Voltage-clamp experiments were carried out with patch pipettes in the tight-seal, whole-cell recording mode or with conventional microelectrodes. Isoproterenol induced a current identified as M current by the following criteria: the induced current is outward and carried by K+ ions, is suppressed by muscarine or acetylcholine, remains steadily activated, turns off with hyperpolarization, and exhibits slow relaxations in response to voltage jumps. In contrast to endogenous M current, isoproterenol-induced M current usually exhibited slower relaxations on hyperpolarizing voltage commands and displayed a steady-state conductance/voltage relationship that was shifted in the negative direction along the voltage axis. M current was also induced by either forskolin or phosphodiesterase-resistant cAMP analogs. In all cases, muscarinic agonists suppressed the M current, apparently by acting at a locus downstream from regulation of cAMP levels by adenylate cyclase and phosphodiesterase. beta-Adrenergic agents may act to increase the number of M channels available to be opened and also modify their kinetics.
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Affiliation(s)
- S M Sims
- Department of Physiology, University of Massachusetts Medical School, Worcester 01655
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Abstract
We performed patch clamp recordings in the whole cell mode from cultured embryonic mouse hippocampal neurons. In bathing solutions containing tetrodotoxin (TTX), the cells showed spontaneous inward currents (SICs) ranging in size from 1 to 100 pA. Several observations indicated that the SICs were miniature excitatory synaptic currents mediated primarily by non-NMDA (N-methyl-D-aspartate) excitatory amino acid receptors: the rising phase of SICs was fast (1 ms to half amplitude at room temperature) and smooth, suggesting unitary events. The SICs were blocked by the broad-spectrum glutamate receptor antagonist gamma-D-glutamylglycine (DGG), but not by the selective NMDA-receptor antagonist D-2-amino-5-phosphonovaleric acid (5-APV). SICs were also blocked by desensitizing concentrations of quisqualate. Incubating cells in tetanus toxin, which blocks exocytotic transmitter release, eliminated SICs. The presence of SICs was consistent with the morphological arrangement of glutamatergic innervation in the cell cultures demonstrated immunohistochemically. Spontaneous outward currents (SOCs) were blocked by bicuculline and presumed to be mediated by GABAA receptors. This is consistent with immunohistochemical demonstration of GABAergic synapses. SIC frequency was increased in a calcium dependent manner by bathing the cells in a solution high in K+, and application of the dihydropyridine L-type calcium channel agonist BAY K 8644 increased the frequency of SICs. Increases in SIC frequency produced by high K+ solutions were reversed by Cd2+ and omega-conotoxin GVIA, but not by the selective L-type channel antagonist nimodipine. This suggested that presynaptic L-type channels were in a gating mode that was not blocked by nimodipine, and/or that another class of calcium channel makes a dominant contribution to excitatory transmitter release.
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Affiliation(s)
- D M Finch
- Department of Neurology, Reed Neurological Research Center, University of California, Los Angeles 90024
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Selyanko AA, Smith PA, Zidichouski JA. Effects of muscarine and adrenaline on neurones from Rana pipiens sympathetic ganglia. J Physiol 1990; 425:471-500. [PMID: 2213586 PMCID: PMC1189859 DOI: 10.1113/jphysiol.1990.sp018114] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
1. Neurones dissociated from Rana pipiens paravertebral sympathetic ganglia were studied by means of the whole-cell patch-clamp technique. Responses to agonists were best recorded when cyclic AMP was included in the patch pipette. 2. Two populations of cells were identified on the basis of size (input capacitance, Cin) and the presence or absence of a fast, transient outward current (A-current, IA). This current was usually present in the 'large' cells (Cin = 40.5 +/- 1.5 pF, n = 66) but absent from 'small' cells (Cin = 21.0 +/- 0.8 pF, n = 70). 3. Both cell types exhibited a slowly activating, non-inactivating K+ current (M-current, IM) which was suppressed by luteinizing hormone-releasing hormone (LHRH, 10-100 microM). Threshold for activation of IM was about -75 mV, half-maximal activation was at -50 mV and the M-conductance GM increased e-fold for at 7 mV change in membrane potential. The maximum value for IM studied in large cells by patch-clamp procedures was less than 0.2 nA. More M-channels were available per unit membrane area in the small cells (GM = 1495 microS cm-2) than in the large cells (GM = 1034 microS cm-2). Time constants for IM deactivation at -70 mV were faster in the large cells (37.2 +/- 4.6 ms, n = 16) than in the small cells (66.1 +/- 5.9 ms, n = 9). 4. Muscarine (10 microM) produced inward current in the large cells as a result of IM suppression. In 40% of the large cells, some of the M-channels were also sensitive to adrenaline (10-100 microM). In a few large cells (less than 10%) adrenaline produced outward current by increasing IM. 5. Muscarine failed to effect IM in the small cells and instead produced an inwardly rectifying K+ current which activated within 5 ms at -110 mV. The outward current produced in twenty out of thirty-seven small cells by adrenaline was occluded by that produced by muscarine, suggesting that both agonists affect the same K+ channels. 6. Inclusion of the protein kinase inhibitors, 1-(5-isoquinolinyl-sulphonyl)-2-methyl piperazine (H-7, 50 microM) or gold sodium thiomalate (GST, 50 microM) in the pipette solution failed to antagonize either muscarine-induced current. Both currents were prolonged when the 'internal solution' contained GTP-gamma-S (50 microM). 7. Phorbol-12-myristate-13-acetate (PMA, 2-5 microM) produced an inward current as a result of IM suppression in both small and large cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A A Selyanko
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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