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BK Ca ( Slo) Channel Regulates Mitochondrial Function and Lifespan in Drosophila melanogaster. Cells 2019; 8:cells8090945. [PMID: 31438578 PMCID: PMC6770356 DOI: 10.3390/cells8090945] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Revised: 08/13/2019] [Accepted: 08/20/2019] [Indexed: 12/20/2022] Open
Abstract
BKCa channels, originally discovered in Drosophila melanogaster as slowpoke (slo), are recognized for their roles in cellular and organ physiology. Pharmacological approaches implicated BKCa channels in cellular and organ protection possibly for their ability to modulate mitochondrial function. However, the direct role of BKCa channels in regulating mitochondrial structure and function is not deciphered. Here, we demonstrate that BKCa channels are present in fly mitochondria, and slo mutants show structural and functional defects in mitochondria. slo mutants display an increase in reactive oxygen species and the modulation of ROS affected their survival. We also found that the absence of BKCa channels reduced the lifespan of Drosophila, and overexpression of human BKCa channels in flies extends life span in males. Our study establishes the presence of BKCa channels in mitochondria of Drosophila and ascertains its novel physiological role in regulating mitochondrial structural and functional integrity, and lifespan.
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Kulik Y, Jones R, Moughamian AJ, Whippen J, Davis GW. Dual separable feedback systems govern firing rate homeostasis. eLife 2019; 8:45717. [PMID: 30973325 PMCID: PMC6491091 DOI: 10.7554/elife.45717] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 04/10/2019] [Indexed: 12/02/2022] Open
Abstract
Firing rate homeostasis (FRH) stabilizes neural activity. A pervasive and intuitive theory argues that a single variable, calcium, is detected and stabilized through regulatory feedback. A prediction is that ion channel gene mutations with equivalent effects on neuronal excitability should invoke the same homeostatic response. In agreement, we demonstrate robust FRH following either elimination of Kv4/Shal protein or elimination of the Kv4/Shal conductance. However, the underlying homeostatic signaling mechanisms are distinct. Eliminating Shal protein invokes Krüppel-dependent rebalancing of ion channel gene expression including enhanced slo, Shab, and Shaker. By contrast, expression of these genes remains unchanged in animals harboring a CRISPR-engineered, Shal pore-blocking mutation where compensation is achieved by enhanced IKDR. These different homeostatic processes have distinct effects on homeostatic synaptic plasticity and animal behavior. We propose that FRH includes mechanisms of proteostatic feedback that act in parallel with activity-driven feedback, with implications for the pathophysiology of human channelopathies.
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Affiliation(s)
- Yelena Kulik
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, United States
| | - Ryan Jones
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, United States
| | - Armen J Moughamian
- Department of Neurology, University of California, San Francisco, San Francisco, United States
| | - Jenna Whippen
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, United States
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, United States
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Bollinger WL, Sial N, Dawson-Scully K. BK channels and a cGMP-dependent protein kinase (PKG) function through independent mechanisms to regulate the tolerance of synaptic transmission to acute oxidative stress at the Drosophila larval neuromuscular junction. J Neurogenet 2018; 32:246-255. [DOI: 10.1080/01677063.2018.1500571] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Wesley L. Bollinger
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
| | - Nadia Sial
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
- Brain Institute Research Scholars Program, Florida Atlantic University, Boca Raton, FL, USA
| | - Ken Dawson-Scully
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
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Ruan H, Ueda A, Xing X, Wan X, Strub B, Mukai S, Certel K, Green D, Belozerov K, Yao WD, Johnson W, Jung-Ching Lin J, Hilliker AJ, Wu CF. Generation and characterization of new alleles of quiver (qvr) that encodes an extracellular modulator of the Shaker potassium channel. J Neurogenet 2017; 31:325-336. [PMID: 29117754 DOI: 10.1080/01677063.2017.1393076] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Our earlier genetic screen uncovered a paraquat-sensitive leg-shaking mutant quiver1 (qvr1), whose gene product interacts with the Shaker (Sh) K+ channel. We also mapped the qvr locus to EY04063 and noticed altered day-night activity patterns in these mutants. Such circadian behavioral defects were independently reported by another group, who employed the qvr1 allele we supplied them, and attributed the extreme restless phenotype of EY04063 to the qvr gene. However, their report adopted a new noncanonical gene name sleepless (sss) for qvr. In addition to qvr1 and qvrEY, our continuous effort since the early 2000s generated a number of novel recessive qvr alleles, including ethyl methanesulfonate (EMS)-induced mutations qvr2 and qvr3, and P-element excision lines qvrip6 (imprecise jumpout), qvrrv7, and qvrrv9 (revertants) derived from qvrEY. Distinct from the original intron-located qvr1 allele that generates abnormal-sized mRNAs, qvr2, and qvr3 had their lesion sites in exons 6 and 7, respectively, producing nearly normal-sized mRNA products. A set of RNA-editing sites are nearby the lesion sites of qvr3 and qvrEY on exon 7. Except for the revertants, all qvr alleles display a clear ether-induced leg-shaking phenotype just like Sh, and weakened climbing abilities to varying degrees. Unlike Sh, all shaking qvr alleles (except for qvrf01257) displayed a unique activity-dependent enhancement in excitatory junction potentials (EJPs) at larval neuromuscular junctions (NMJs) at very low stimulus frequencies, with qvrEY displaying the largest EJP and more significant NMJ overgrowth than other alleles. Our detailed characterization of a collection of qvr alleles helps to establish links between novel molecular lesions and different behavioral and physiological consequences, revealing how modifications of the qvr gene lead to a wide spectrum of phenotypes, including neuromuscular hyperexcitability, defective motor ability and activity-rest cycles.
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Affiliation(s)
- Hongyu Ruan
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Atsushi Ueda
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Xiaomin Xing
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Xuxuan Wan
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Benjamin Strub
- b Department of Biology , York University , Toronto , ON , Canada
| | - Spencer Mukai
- b Department of Biology , York University , Toronto , ON , Canada
| | - Kaan Certel
- c Department of Molecular Physiology and Biophysics , University of Iowa , Iowa City , IA , USA
| | - David Green
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Kyle Belozerov
- b Department of Biology , York University , Toronto , ON , Canada
| | - Wei-Dong Yao
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Wayne Johnson
- c Department of Molecular Physiology and Biophysics , University of Iowa , Iowa City , IA , USA
| | | | | | - Chun-Fang Wu
- a Department of Biology , University of Iowa , Iowa City , IA , USA
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Saur T, Peng IF, Jiang P, Gong N, Yao WD, Xu TL, Wu CF. K + channel reorganization and homeostatic plasticity during postembryonic development: biophysical and genetic analyses in acutely dissociated Drosophila central neurons. J Neurogenet 2016; 30:259-275. [PMID: 27868467 PMCID: PMC5918286 DOI: 10.1080/01677063.2016.1255212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 10/27/2016] [Accepted: 10/27/2016] [Indexed: 10/20/2022]
Abstract
Intrinsic electric activities of neurons play important roles in establishing and refining neural circuits during development. However, how the underlying ionic currents undergo postembryonic reorganizations remains largely unknown. Using acutely dissociated neurons from larval, pupal, and adult Drosophila brains, we show drastic re-assemblies and compensatory regulations of voltage-gated (IKv) and Ca2+-activated (IK(Ca)) K+ currents during postembryonic development. Larval and adult neurons displayed prominent fast-inactivating IKv, mediated by the Shaker (Sh) channel to a large extent, while in the same neurons IK(Ca) was far smaller in amplitude. In contrast, pupal neurons were characterized by large sustained IKv and prominent IK(Ca), encoded predominantly by the slowpoke (slo) gene. Surprisingly, deletion of Sh in the ShM null mutant removed inactivating, transient IKv from large portions of neurons at all stages. Interestingly, elimination of Sh currents was accompanied by upregulation of non-Sh transient IKv. In comparison, the slo1 mutation abolished the vast majority of IK(Ca), particularly at the pupal stage. Strikingly, the deficiency of IK(Ca) in slo pupae was compensated by the transient component of IKv mediated by Sh channels. Thus, IK(Ca) appears to play critical roles in pupal development and its absence induces functional compensations from a specific transient IKv current. While mutants lacking either Sh or slo currents survived normally, Sh;;slo double mutants deficient in both failed to survive through pupal metamorphosis. Together, our data highlight significant reorganizations and homeostatic compensations of K+ currents during postembryonic development and uncover previously unrecognized roles for Sh and slo in this plastic process.
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Affiliation(s)
- Taixiang Saur
- a Department of Neurobiology and Biophysics , School of Life Sciences, University of Science and Technology of China , Hefei , China
- b Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai , China
- c New England Primate Research Center, Harvard Medical School , Southborough , MA , USA
| | - I-Feng Peng
- d Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Peng Jiang
- a Department of Neurobiology and Biophysics , School of Life Sciences, University of Science and Technology of China , Hefei , China
- b Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai , China
| | - Neng Gong
- a Department of Neurobiology and Biophysics , School of Life Sciences, University of Science and Technology of China , Hefei , China
- b Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai , China
| | - Wei-Dong Yao
- c New England Primate Research Center, Harvard Medical School , Southborough , MA , USA
| | - Tian-Le Xu
- a Department of Neurobiology and Biophysics , School of Life Sciences, University of Science and Technology of China , Hefei , China
- b Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai , China
| | - Chun-Fang Wu
- a Department of Neurobiology and Biophysics , School of Life Sciences, University of Science and Technology of China , Hefei , China
- b Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences , Shanghai , China
- d Department of Biology , University of Iowa , Iowa City , IA , USA
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The influence of postsynaptic structure on missing quanta at the Drosophila neuromuscular junction. BMC Neurosci 2016; 17:53. [PMID: 27459966 PMCID: PMC4962461 DOI: 10.1186/s12868-016-0290-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 07/20/2016] [Indexed: 11/10/2022] Open
Abstract
Background Synaptic transmission requires both pre- and post-synaptic elements for neural communication. The postsynaptic structure contributes to the ability of synaptic currents to induce voltage changes in postsynaptic cells. At the Drosophila neuromuscular junction (NMJ), the postsynaptic structure, known as the subsynaptic reticulum (SSR), consists of elaborate membrane folds that link the synaptic contacts to the muscle, but its role in synaptic physiology is poorly understood. Results In this study, we investigate the role of the SSR with simultaneous intra- and extra-cellular recordings that allow us to identify the origin of spontaneously occurring synaptic events. We compare data from Type 1b and 1s synaptic boutons, which have naturally occurring variations of the SSR, as well as from genetic mutants that up or down-regulate SSR complexity. We observed that some synaptic currents do not result in postsynaptic voltage changes, events we called ‘missing quanta’. The frequency of missing quanta is positively correlated with SSR complexity in both natural and genetically-induced variants. Rise-time and amplitude data suggest that passive membrane properties contribute to the observed differences in synaptic effectiveness. Conclusion We conclude that electrotonic decay within the postsynaptic structure contributes to the phenomenon of missing quanta. Further studies directed at understanding the role of the SSR in synaptic transmission and the potential for regulating ‘missing quanta’ will yield important information about synaptic transmission at the Drosophila NMJ.
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Kadas D, Ryglewski S, Duch C. Transient BK outward current enhances motoneurone firing rates during Drosophila larval locomotion. J Physiol 2015; 593:4871-88. [PMID: 26332699 DOI: 10.1113/jp271323] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 08/21/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS We combine in situ electrophysiology with genetic manipulation in Drosophila larvae aiming to investigate the role of fast calcium-activated potassium currents for motoneurone firing patterns during locomotion. We first demonstrate that slowpoke channels underlie fast calcium-activated potassium currents in these motoneurones. By conducting recordings in semi-intact animals that produce crawling-like movements, we show that slowpoke channels are required specifically in motoneurones for maximum firing rates during locomotion. Such enhancement of maximum firing rates occurs because slowpoke channels prevent depolarization block by limiting the amplitude of motoneurone depolarization in response to synaptic drive. In addition, slowpoke channels mediate a fast afterhyperpolarization that ensures the efficient recovery of sodium channels from inactivation during high frequency firing. The results of the present study provide new insights into the mechanisms by which outward conductances facilitate neuronal excitability and also provide direct confirmation of the functional relevance of precisely regulated slowpoke channel properties in motor control. ABSTRACT A large number of voltage-gated ion channels, their interactions with accessory subunits, and their post-transcriptional modifications generate an immense functional diversity of neurones. Therefore, a key challenge is to understand the genetic basis and precise function of specific ionic conductances for neuronal firing properties in the context of behaviour. The present study identifies slowpoke (slo) as exclusively mediating fast activating, fast inactivating BK current (ICF ) in larval Drosophila crawling motoneurones. Combining in vivo patch clamp recordings during larval crawling with pharmacology and targeted genetic manipulations reveals that ICF acts specifically in motoneurones to sculpt their firing patterns in response to a given input from the central pattern generating (CPG) networks. First, ICF curtails motoneurone postsynaptic depolarizations during rhythmical CPG drive. Second, ICF is activated during the rising phase of the action potential and mediates a fast afterhyperpolarization. Consequently, ICF is required for maximal intraburst firing rates during locomotion, probably by allowing recovery from inactivation of fast sodium channels and decreased potassium channel activation. This contrasts the common view that outward conductances oppose excitability but is in accordance with reports on transient BK and Kv3 channel function in multiple types of vertebrate neurones. Therefore, our finding that ICF enhances firing rates specifically during bursting patterns relevant to behaviour is probably of relevance to all brains.
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Affiliation(s)
- Dimitrios Kadas
- Institute of Neurobiology, Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Stefanie Ryglewski
- Institute of Neurobiology, Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Carsten Duch
- Institute of Neurobiology, Johannes Gutenberg University of Mainz, Mainz, Germany
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Gertner DM, Desai S, Lnenicka GA. Synaptic excitation is regulated by the postsynaptic dSK channel at the Drosophila larval NMJ. J Neurophysiol 2014; 111:2533-43. [PMID: 24671529 DOI: 10.1152/jn.00903.2013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the mammalian central nervous system, the postsynaptic small-conductance Ca(2+)-dependent K(+) (SK) channel has been shown to reduce postsynaptic depolarization and limit Ca(2+) influx through N-methyl-d-aspartate receptors. To examine further the role of the postsynaptic SK channel in synaptic transmission, we studied its action at the Drosophila larval neuromuscular junction (NMJ). Repetitive synaptic stimulation produced an increase in postsynaptic membrane conductance leading to depression of excitatory postsynaptic potential amplitude and hyperpolarization of the resting membrane potential (RMP). This reduction in synaptic excitation was due to the postsynaptic Drosophila SK (dSK) channel; synaptic depression, increased membrane conductance and RMP hyperpolarization were reduced in dSK mutants or after expressing a Ca(2+) buffer in the muscle. Ca(2+) entering at the postsynaptic membrane was sufficient to activate dSK channels based upon studies in which the muscle membrane was voltage clamped to prevent opening voltage-dependent Ca(2+) channels. Increasing external Ca(2+) produced an increase in resting membrane conductance and RMP that was not seen in dSK mutants or after adding the glutamate-receptor blocker philanthotoxin. Thus it appeared that dSK channels were also activated by spontaneous transmitter release and played a role in setting membrane conductance and RMP. In mammals, dephosphorylation by protein phosphatase 2A (PP2A) increased the Ca(2+) sensitivity of the SK channel; PP2A appeared to increase the sensitivity of the dSK channel since PP2A inhibitors reduced activation of the dSK channel by evoked synaptic activity or increased external Ca(2+). It is proposed that spontaneous and evoked transmitter release activate the postsynaptic dSK channel to limit synaptic excitation and stabilize synapses.
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Affiliation(s)
- Daniel M Gertner
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Sunil Desai
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, Albany, New York
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McKiernan EC. Effects of manipulating slowpoke calcium-dependent potassium channel expression on rhythmic locomotor activity in Drosophila larvae. PeerJ 2013; 1:e57. [PMID: 23638395 PMCID: PMC3628981 DOI: 10.7717/peerj.57] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Accepted: 03/05/2013] [Indexed: 11/20/2022] Open
Abstract
Rhythmic motor behaviors are generated by networks of neurons. The sequence and timing of muscle contractions depends on both synaptic connections between neurons and the neurons' intrinsic properties. In particular, motor neuron ion currents may contribute significantly to motor output. Large conductance Ca(2+)-dependent K(+) (BK) currents play a role in action potential repolarization, interspike interval, repetitive and burst firing, burst termination and interburst interval in neurons. Mutations in slowpoke (slo) genes encoding BK channels result in motor disturbances. This study examined the effects of manipulating slo channel expression on rhythmic motor activity using Drosophila larva as a model system. Dual intracellular recordings from adjacent body wall muscles were made during spontaneous crawling-related activity in larvae expressing a slo mutation or a slo RNA interference construct. The incidence and duration of rhythmic activity in slo mutants were similar to wild-type control animals, while the timing of the motor pattern was altered. slo mutants showed decreased burst durations, cycle durations, and quiescence intervals, and increased duty cycles, relative to wild-type. Expressing slo RNAi in identified motor neurons phenocopied many of the effects observed in the mutant, including decreases in quiescence interval and cycle duration. Overall, these results show that altering slo expression in the whole larva, and specifically in motor neurons, changes the frequency of crawling activity. These results suggest an important role for motor neuron intrinsic properties in shaping the timing of motor output.
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Affiliation(s)
- Erin C McKiernan
- Instituto Tecnológico y de Estudios Superiores de Monterrey , Xochitepec, Morelos , México
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The Drosophila SK channel (dSK) contributes to photoreceptor performance by mediating sensitivity control at the first visual network. J Neurosci 2011; 31:13897-910. [PMID: 21957252 DOI: 10.1523/jneurosci.3134-11.2011] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The contribution of the SK (small-conductance calcium-activated potassium) channel to neuronal functions in complex circuits underlying sensory processing and behavior is largely unknown in the absence of suitable animal models. Here, we generated a Drosophila line that lacks the single highly conserved SK gene in its genome (dSK). In R1-R6 photoreceptors, dSK encodes a slow Ca²⁺-activated K(+) current similar to its mammalian counterparts. Compared with wild-type, dSK(-) photoreceptors and interneurons showed accelerated oscillatory responses and adaptation. These enhanced kinetics were accompanied with more depolarized dSK(-) photoreceptors axons, assigning a role for dSK in network gain control during light-to-dark transitions. However, compensatory network adaptation, through increasing activity between synaptic neighbors, overcame many detriments of missing dSK current enabling dSK(-) photoreceptors to maintain normal information transfer rates to naturalistic stimuli. While demonstrating important functional roles for dSK channel in the visual circuitry, these results also clarify how homeostatically balanced network functions can compensate missing or faulty ion channels.
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11
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Abstract
Synapse formation is tightly associated with neuronal excitability. We found striking synaptic overgrowth caused by Drosophila K(+)-channel mutations of the seizure and slowpoke genes, encoding Erg and Ca(2+)-activated large-conductance (BK) channels, respectively. These mutants display two distinct patterns of "satellite" budding from larval motor terminus synaptic boutons. Double-mutant analysis indicates that BK and Erg K(+) channels interact with separate sets of synaptic proteins to affect distinct growth steps. Post-synaptic L-type Ca(2+) channels, Dmca1D, and PSD-95-like scaffold protein, Discs large, are required for satellite budding induced by slowpoke and seizure mutations. Pre-synaptic cacophony Ca(2+) channels and the NCAM-like adhesion molecule, Fasciclin II, take part in a maturation step that is partially arrested by seizure mutations. Importantly, slowpoke and seizure satellites were both suppressed by rutabaga mutations that disrupt Ca(2+)/CaM-dependent adenylyl cyclase, demonstrating a convergence of K(+) channels of different functional categories in regulation of excitability-dependent Ca(2+) influx for triggering cAMP-mediated growth plasticity.
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Peron S, Zordan MA, Magnabosco A, Reggiani C, Megighian A. From action potential to contraction: neural control and excitation-contraction coupling in larval muscles of Drosophila. Comp Biochem Physiol A Mol Integr Physiol 2009; 154:173-83. [PMID: 19427393 DOI: 10.1016/j.cbpa.2009.04.626] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 04/16/2009] [Accepted: 04/22/2009] [Indexed: 11/17/2022]
Abstract
The neuromuscular system of Drosophila melanogaster has been studied for many years for its relative simplicity and because of the genetic and molecular versatilities. Three main types of striated muscles are present in this dipteran: fibrillar muscles, tubular muscles and supercontractile muscles. The visceral muscles in adult flies and the body wall segmental muscles in embryos and larvae belong to the group of supercontractile muscles. Larval body wall muscles have been the object of detailed studies as a model for neuromuscular junction function but have received much less attention with respect to their mechanical properties and to the control of contraction. In this review we wish to assess available information on the physiology of the Drosophila larval muscular system. Our aim is to establish whether this system has the requisites to be considered a good model in which to perform a functional characterization of Drosophila genes, with a known muscular expression, as well as Drosophila homologs of human genes, the dysfunction of which, is known to be associated with human hereditary muscle pathologies.
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Affiliation(s)
- Samantha Peron
- Department of Anatomy and Physiology, University of Padua, Italy
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Joiner MA, Asztalos Z, Jones CJ, Tully T, Wu CF. Effects of mutant Drosophila K+ channel subunits on habituation of the olfactory jump response. J Neurogenet 2007; 21:45-58. [PMID: 17464797 PMCID: PMC3045562 DOI: 10.1080/01677060701247375] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The olfactory-jump response assay was used to analyze habituation in Drosophila mutants of potassium (K(+)) channel subunits. As with physiological assays of the giant fiber-mediated escape reflex, mutations at loci that encode K(+) channel subunits have distinct effects on habituating the olfactory-jump response. The data for slowpoke and ether à go-go indicate similar effects on habituation of the olfactory-jump response and the giant fiber-mediated escape. Habituation in the olfactory jump assay in Hyperkinetic and Shaker mutants was drastically different from the degree of defect in the giant fiber-mediated escape reflex, indicating differential control mechanisms underlying the two forms of non-associative conditioning.
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Affiliation(s)
- M A Joiner
- Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA
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14
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Peng IF, Wu CF. Drosophila cacophony channels: a major mediator of neuronal Ca2+ currents and a trigger for K+ channel homeostatic regulation. J Neurosci 2007; 27:1072-81. [PMID: 17267561 PMCID: PMC6673189 DOI: 10.1523/jneurosci.4746-06.2007] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2006] [Revised: 12/20/2006] [Accepted: 12/21/2006] [Indexed: 11/21/2022] Open
Abstract
The cacophony (cac) locus in Drosophila encodes a Ca2+ channel alpha subunit, but little is known about properties of cac-mediated currents and functional consequences of cac mutations in central neurons. We found that, in Drosophila cultured neurons, Ca2+ currents were mediated predominantly by the cac channels. The cac channels contribute to low- and high-threshold, fast- and slow-inactivating types of Ca2+ currents, take part in membrane depolarization, and strongly activate Ca2+-activated K+ current [I(K(Ca))]. In cac neurons, unexpectedly, voltage-activated transient K+ current I(A) is upregulated to a level that matches I(K(Ca)) reduction, implicating a homeostatic regulation that was mimicked by chronic pharmacological blockade of Ca2+ currents in wild-type neurons. Among K+ channel transcripts, Shaker mRNA levels were preferentially increased in cac flies. However, Ca2+ current expression levels remained unaltered in several K+ channel mutants, illustrating a key role of cac in developmental regulation of Drosophila neuronal excitability.
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Affiliation(s)
- I-Feng Peng
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242
| | - Chun-Fang Wu
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242
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15
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Berke BA, Lee J, Peng IF, Wu CF. Sub-cellular Ca2+ dynamics affected by voltage- and Ca2+-gated K+ channels: Regulation of the soma-growth cone disparity and the quiescent state in Drosophila neurons. Neuroscience 2006; 142:629-44. [PMID: 16919393 DOI: 10.1016/j.neuroscience.2006.06.051] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 06/06/2006] [Accepted: 06/23/2006] [Indexed: 11/24/2022]
Abstract
Using Drosophila mutants and pharmacological blockers, we provide the first evidence that distinct types of K(+) channels differentially influence sub-cellular Ca(2+) regulation and growth cone morphology during neuronal development. Fura-2-based imaging revealed in cultured embryonic neurons that the loss of either voltage-gated, inactivating Shaker channels or Ca(2+)-gated Slowpoke BK channels led to robust spontaneous Ca(2+) transients that preferentially occurred within the growth cone. In contrast, loss of voltage-gated, non-inactivating Shab channels did not show such a disparity and sometimes produced soma-specific Ca(2+) transients. The fast spontaneous transients in both the soma and growth cone were suppressed by the Na(+) channel blocker tetrodotoxin, indicating that these Ca(2+) fluctuations stemmed from increases in membrane excitability. Similar differences in regional Ca(2+) regulation were observed upon membrane depolarization by high K(+)-containing saline. In particular, Shaker and slowpoke mutations enhanced the size and dynamics of the depolarization-induced Ca(2+) increase in the growth cone. In contrast, Shab mutations greatly prolonged the Ca(2+) increase in the soma. Differential effects of these excitability mutations on neuronal development were indicated by their distinct alterations in growth cone morphology. Loss of Shaker currents increased the size of lamellipodia and the number of filopodia, structures associated with the actin cytoskeleton. Interestingly, loss of Slowpoke currents strongly influenced tubulin regulation, enhancing the number of microtubule loop structures per growth cone. Together, our findings support the idea that individual K(+) channel subunits differentially regulate spontaneous sub-cellular Ca(2+) fluctuations in growing neurons that may influence activity-dependent growth cone formation.
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Affiliation(s)
- B A Berke
- Interdisciplinary Program in Neuroscience, University of Iowa, Iowa City, IA 52242, USA.
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16
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Derst C, Walther C, Veh RW, Wicher D, Heinemann SH. Four novel sequences in Drosophila melanogaster homologous to the auxiliary Para sodium channel subunit TipE. Biochem Biophys Res Commun 2005; 339:939-48. [PMID: 16325765 DOI: 10.1016/j.bbrc.2005.11.096] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Accepted: 11/12/2005] [Indexed: 11/25/2022]
Abstract
TipE is an auxiliary subunit of the Drosophila Para sodium channel. Here we describe four sequences, TEH1-4, homologous to TipE in the Drosophila melanogaster genome, harboring all typical structures of both TipE and the beta-Subunit family of big-conductance Ca(2+)-activated potassium channels: short cytosolic N- and C-terminal stretches, two transmembrane domains, and a large extracellular loop with two disulfide bonds. Whereas TEH1 and TEH2 lack the TipE-specific extension in the extracellular loop, both TEH3 and TEH4 possess two extracellular EGF-like domains. A CNS-specific expression was found for TEH1, while TEH2-4 were more widely expressed. The genes for TEH2-4 are localized close to the tipE gene on chromosome 3L. Coexpression of TEH subunits with Para in Xenopus oocytes showed a strong (30-fold, TEH1), medium (5- to 10-fold, TEH2 and TEH3), or no (TEH4) increase in sodium current amplitude, while TipE increased the current 20-fold. In addition, steady-state inactivation and the recovery from fast inactivation were altered by coexpression of Para with TEH1. We conclude that members of the TEH-family are auxiliary subunits for Para sodium channels and possibly other ion channels.
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Affiliation(s)
- Christian Derst
- Center for Anatomy, Charité Berlin, Philippstr. 12, 10115 Berlin, Germany
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17
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Wicher D, Walther C, Wicher C. Non-synaptic ion channels in insects--basic properties of currents and their modulation in neurons and skeletal muscles. Prog Neurobiol 2001; 64:431-525. [PMID: 11301158 DOI: 10.1016/s0301-0082(00)00066-6] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Insects are favoured objects for studying information processing in restricted neuronal networks, e.g. motor pattern generation or sensory perception. The analysis of the underlying processes requires knowledge of the electrical properties of the cells involved. These properties are determined by the expression pattern of ionic channels and by the regulation of their function, e.g. by neuromodulators. We here review the presently available knowledge on insect non-synaptic ion channels and ionic currents in neurons and skeletal muscles. The first part of this article covers genetic and structural informations, the localization of channels, their electrophysiological and pharmacological properties, and known effects of second messengers and modulators such as neuropeptides or biogenic amines. In a second part we describe in detail modulation of ionic currents in three particularly well investigated preparations, i.e. Drosophila photoreceptor, cockroach DUM (dorsal unpaired median) neuron and locust jumping muscle. Ion channel structures are almost exclusively known for the fruitfly Drosophila, and most of the information on their function has also been obtained in this animal, mainly based on mutational analysis and investigation of heterologously expressed channels. Now the entire genome of Drosophila has been sequenced, it seems almost completely known which types of channel genes--and how many of them--exist in this animal. There is much knowledge of the various types of channels formed by 6-transmembrane--spanning segments (6TM channels) including those where four 6TM domains are joined within one large protein (e.g. classical Na+ channel). In comparison, two TM channels and 4TM (or tandem) channels so far have hardly been explored. There are, however, various well characterized ionic conductances, e.g. for Ca2+, Cl- or K+, in other insect preparations for which the channels are not yet known. In some of the larger insects, i.e. bee, cockroach, locust and moth, rather detailed information has been established on the role of ionic currents in certain physiological or behavioural contexts. On the whole, however, knowledge of non-synaptic ion channels in such insects is still fragmentary. Modulation of ion currents usually involves activation of more or less elaborate signal transduction cascades. The three detailed examples for modulation presented in the second part indicate, amongst other things, that one type of modulator usually leads to concerted changes of several ion currents and that the effects of different modulators in one type of cell may overlap. Modulators participate in the adaptive changes of the various cells responsible for different physiological or behavioural states. Further study of their effects on the single cell level should help to understand how small sets of cells cooperate in order to produce the appropriate output.
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Affiliation(s)
- D Wicher
- Sächsische Akademie der Wissenschaften zu Leipzig, Arbeitsgruppe Neurohormonale Wirkungsmechanismen, Erbertstr. 1, 07743, Jena, Germany.
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18
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A novel leg-shaking Drosophila mutant defective in a voltage-gated K(+)current and hypersensitive to reactive oxygen species. J Neurosci 2000. [PMID: 10934243 DOI: 10.1523/jneurosci.20-16-05958.2000] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
1,1'-Dimethyl-4,4'-bipyridinium dichloride (methyl viologen; paraquat), an herbicide that causes depletion of NADPH and generates excessive reactive oxygen species (ROS) in vivo, has been used to screen for ROS-sensitive Drosophila mutants. One mutant so isolated, named quiver(1) (qvr(1)), has a leg-shaking phenotype. Mutants of the Shaker (Sh), Hyperkinetic (Hk), and ether a go-go (eag) genes, which encode different K(+) channel subunits that regulate the A-type K(+) current (I(A)) in different ways, exhibit leg shaking under ether anesthesia and have heightened metabolic rates and shortened life spans. We found that Sh, Hk, and eag mutant flies were all hypersensitive to paraquat. Double-mutant combinations among the three channel mutations and qvr(1) had drastically enhanced sensitivity to paraquat. Synaptic transmission at the larval neuromuscular junction was increased in the qvr(1) mutant to the level of Sh mutants. Similar to eag Sh double mutants, double mutants of eag and qvr(1) showed striking enhancement in synaptic transmission and a wings-down phenotype, the hallmarks of extreme hyperexcitability. Voltage-clamp experiments demonstrated that the qvr(1) mutation specifically disrupted the Sh-dependent I(A) current without altering the other currents [I(K), Ca(2+)-activated fast (I(CF)) and slow (I(CS)) currents, and I(Ca)] in larval muscles. Several deficiency strains of the qvr locus failed to complement qvr(1) and confirmed that ether-induced leg shaking, reduced I(A) current, and paraquat hypersensitivity map to the same locus. Our results suggest that the qvr gene may encode a novel K(+) channel-related polypeptide and indicate a strong link between a voltage-activated K(+) current and vulnerability to ROS.
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19
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Molecular separation of two behavioral phenotypes by a mutation affecting the promoters of a Ca-activated K channel. J Neurosci 2000. [PMID: 10751451 DOI: 10.1523/jneurosci.20-08-02988.2000] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Drosophila slowpoke gene encodes a BK-type calcium-activated potassium channel. Null mutations in slowpoke perturb the signaling properties of neurons and muscles and cause behavioral defects. The animals fly very poorly compared with wild-type strains and, after exposure to a bright but cool light or a heat pulse, exhibit a "sticky-feet" phenotype. Expression of slowpoke arises from five transcriptional promoters that express the gene in neural, muscle, and epithelial tissues. A chromosomal deletion (ash2(18)) has been identified that removes the neuronal promoters but not the muscle-tracheal cell promoter. This deletion complements the flight defect of slowpoke null mutants but not the sticky-feet phenotype. Electrophysiological assays confirm that the ash2(18) chromosome restores normal electrical properties to the flight muscle. This suggests that the flight defect arises from a lack of slowpoke expression in muscle, whereas the sticky-feet phenotype arises from a lack of expression in nervous tissue.
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20
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Meir A, Ginsburg S, Butkevich A, Kachalsky SG, Kaiserman I, Ahdut R, Demirgoren S, Rahamimoff R. Ion channels in presynaptic nerve terminals and control of transmitter release. Physiol Rev 1999; 79:1019-88. [PMID: 10390521 DOI: 10.1152/physrev.1999.79.3.1019] [Citation(s) in RCA: 220] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The primary function of the presynaptic nerve terminal is to release transmitter quanta and thus activate the postsynaptic target cell. In almost every step leading to the release of transmitter quanta, there is a substantial involvement of ion channels. In this review, the multitude of ion channels in the presynaptic terminal are surveyed. There are at least 12 different major categories of ion channels representing several tens of different ion channel types; the number of different ion channel molecules at presynaptic nerve terminals is many hundreds. We describe the different ion channel molecules at the surface membrane and inside the nerve terminal in the context of their possible role in the process of transmitter release. Frequently, a number of different ion channel molecules, with the same basic function, are present at the same nerve terminal. This is especially evident in the cases of calcium channels and potassium channels. This abundance of ion channels allows for a physiological and pharmacological fine tuning of the process of transmitter release and thus of synaptic transmission.
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Affiliation(s)
- A Meir
- Department of Physiology and the Bernard Katz Minerva Centre for Cell Biophysics, Hebrew University Hadassah Medical School, Jerusalem, Israel
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21
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Genetic dissection of functional contributions of specific potassium channel subunits in habituation of an escape circuit in Drosophila. J Neurosci 1998. [PMID: 9482810 DOI: 10.1523/jneurosci.18-06-02254.1998] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Potassium channels have been implicated in central roles in activity-dependent neural plasticity. The giant fiber escape pathway of Drosophila has been established as a model for analyzing habituation and its modification by memory mutations in an identified circuit. Several genes in Drosophila encoding K+ channel subunits have been characterized, permitting examination of the contributions of specific channel subunits to simple conditioning in an identified circuit that is amenable to genetic analysis. Our results show that mutations altering each of four K+ channel subunits (Sh, slo, eag, and Hk) have distinct effects on habituation at least as strong as those of dunce and rutabaga, memory mutants with defective cAMP metabolism (). Habituation, spontaneous recovery, and dishabituation of the electrically stimulated long-latency giant fiber pathway response were shown in each mutant type. Mutations of Sh (voltage-gated) and slo (Ca2+-gated) subunits enhanced and slowed habituation, respectively. However, mutations of eag and Hk subunits, which confer K+-current modulation, had even more extreme phenotypes, again enhancing and slowing habituation, respectively. In double mutants, Sh mutations moderated the strong phenotypes of eag and Hk, suggesting that their modulatory functions are best expressed in the presence of intact Sh subunits. Nonactivity-dependent responses (refractory period and latency) at two stages of the circuit were altered only in some mutants and do not account for modifications of habituation. Furthermore, failures of the long-latency response during habituation, which normally occur in labile connections in the brain, could be induced in the thoracic circuit stage in Hk mutants. Our work indicates that different K+ channel subunits play distinct roles in activity-dependent neural plasticity and thus can be incorporated along with second messenger "memory" loci to enrich the genetic analysis of learning and memory.
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22
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Abstract
We have performed direct electrophysiological recordings from Drosophila peptidergic synaptic boutons in situ, taking advantage of a mutation, ecdysone, which causes an increase in size of these terminals. Using patch-clamp techniques, we have analyzed voltage-dependent potassium currents at the macroscopic and single-channel level. The synaptic membrane contained at least two distinct voltage-activated potassium currents with different kinetics and voltage sensitivity: an IA-like current with fast activation and inactivation kinetics and voltage-dependent steady-state inactivation; a complex delayed current that includes a slowly inactivating component, resembling the IK described in other preparations; and a noninactivating component. The IA-like current in these peptidergic boutons is not encoded by the gene Shaker, because it is not affected by null mutations at this locus. Rather, synaptic IA has properties similar to those of the Shal-encoded IA. Single-channel recordings revealed the presence in synaptic membranes of three different potassium channel types (A2, KD, KL), with biophysical properties that could account for the macroscopic currents and resemble those of the Shal, Shab, and Shaw channels described in heterologous expression systems and Drosophila neuronal somata. A2 channels (6-9 pS) have brief open times, and like the macroscopic IA they exhibited voltage-dependent steady-state inactivation and a rapidly inactivating ensemble average current profile. KD channels (13-16 pS) had longer open times, activate and inactivate with much slower kinetics, and may account for the slowly inactivating component of the macroscopic current. KL (44-54 pS) channels produced a noninactivating ensemble average and may contribute to the delayed macroscopic current observed.
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23
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Wang JW, Wu CF. In vivo functional role of the Drosophila hyperkinetic beta subunit in gating and inactivation of Shaker K+ channels. Biophys J 1996; 71:3167-76. [PMID: 8968587 PMCID: PMC1233805 DOI: 10.1016/s0006-3495(96)79510-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The physiological roles of the beta, or auxiliary, subunits of voltage-gated ion channels, including Na+, Ca2+, and K+ channels, have not been demonstrated directly in vivo. Drosophila Hyperkinetic (Hk) mutations alter a gene encoding a homolog of the mammalian K+ channel beta subunit, providing a unique opportunity to delineate the in vivo function of auxiliary subunits in K+ channels. We found that the Hk beta subunit modulates a wide range of the Shaker (Sh) K+ current properties, including its amplitude, activation and inactivation, temperature dependence, and drug sensitivity. Characterizations of the existing mutants in identified muscle cells enabled an analysis of potential mechanisms of subunit interactions and their functional consequences. The results are consistent with the idea that via hydrophobic interaction, Hk beta subunits modulate Sh channel conformation in the cytoplasmic pore region. The modulatory effects of the Hk beta subunit appeared to be specific to the Sh alpha subunit because other voltage- and Ca(2+)-activated K+ currents were not affected by Hk mutations. The mutant effects were especially pronounced near the voltage threshold of IA activation, which can disrupt the maintenance of the quiescent state and lead to the striking neuromuscular and behavioral hyperexcitability previously reported.
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Affiliation(s)
- J W Wang
- Department of Biological Sciences, University of Iowa, Iowa City 52242, USA
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24
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Abstract
Cultured "giant" Drosophila neurons derived from cytokinesis-arrested embryonic neuroblasts express various membrane channels and excitability patterns. Both current- and voltage-clamp recordings could be performed on the same neuron owing to the large cell size, thus making it possible to elucidate the functional role of individual types of channels. This culture system has been used to analyze the mutational perturbations in ion channels and the resultant alterations in membrane excitability.
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Affiliation(s)
- M Saito
- Department of Biology, University of Iowa, Iowa City 52242
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25
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Adelman JP, Shen KZ, Kavanaugh MP, Warren RA, Wu YN, Lagrutta A, Bond CT, North RA. Calcium-activated potassium channels expressed from cloned complementary DNAs. Neuron 1992; 9:209-16. [PMID: 1497890 DOI: 10.1016/0896-6273(92)90160-f] [Citation(s) in RCA: 386] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Calcium-activated potassium channels were expressed in Xenopus oocytes by injection of RNA transcribed in vitro from complementary DNAs derived from the slo locus of Drosophila melanogaster. Many cDNAs were found that encode closely related proteins of about 1200 aa. The predicted sequences of these proteins differ by the substitution of blocks of amino acids at five identified positions within the putative intracellular region between residues 327 and 797. Excised inside-out membrane patches showed potassium channel openings only with micromolar calcium present at the cytoplasmic side; activity increased steeply both with depolarization and with increasing calcium concentration. The single-channel conductance was 126 pS with symmetrical potassium concentrations. The mean open time of the channels was clearly different for channels having different substituent blocks of amino acids. The results suggest that alternative splicing gives rise to a large family of functionally diverse, calcium-activated potassium channels.
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Affiliation(s)
- J P Adelman
- Vollum Institute, Oregon Health Sciences University, Portland 97201
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26
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Affiliation(s)
- C F Wu
- Department of Biology, University of Iowa, Iowa City 52242
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27
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Atkinson NS, Robertson GA, Ganetzky B. A component of calcium-activated potassium channels encoded by the Drosophila slo locus. Science 1991; 253:551-5. [PMID: 1857984 DOI: 10.1126/science.1857984] [Citation(s) in RCA: 487] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Calcium-activated potassium channels mediate many biologically important functions in electrically excitable cells. Despite recent progress in the molecular analysis of voltage-activated K+ channels, Ca(2+)-activated K+ channels have not been similarly characterized. The Drosophila slowpoke (slo) locus, mutations of which specifically abolish a Ca(2+)-activated K+ current in muscles and neurons, provides an opportunity for molecular characterization of these channels. Genomic and complementary DNA clones from the slo locus were isolated and sequenced. The polypeptide predicted by slo is similar to voltage-activated K+ channel polypeptides in discrete domains known to be essential for function. Thus, these results indicate that slo encodes a structural component of Ca(2+)-activated K+ channels.
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Affiliation(s)
- N S Atkinson
- Laboratory of Genetics, University of Wisconsin, Madison 53706
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28
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Latorre R, Bacigalupo J, Delgado R, Labarca P. Four cases of direct ion channel gating by cyclic nucleotides. J Bioenerg Biomembr 1991; 23:577-97. [PMID: 1655722 DOI: 10.1007/bf00785812] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Four different nucleotide-gated ion channels are discussed in terms of their biophysical properties and their importance in cell physiology. Channels activated directly by cGMP are present in vertebrate and invertebrate photoreceptors. In both cases cGMP increases the fraction of time the channel remains in the open state. At least three cGMP molecules are involved in channel opening in vertebrate photoreceptors and the concentration of the cyclic nucleotide to obtain the half maximal effect is about 15 microM. The light-dependent channel of both vertebrates and invertebrates is poorly cation selective. The vertebrate channel allows divalent cations to pass through 10-15-fold more easily than monovalent ions. In agreement with their preference for divalent cations, this channel is blocked by l-cis Dialtazem, a molecule that blocks certain types of calcium channels. In olfactory neurons a channel activated by both cAMP and cGMP is found and, as in the light-dependent channel, several molecules of the nucleotide are needed to open the channel with a half maximal effect obtained in the range of 1-40 microM. The channel is poorly cationic selective. A K+ channel directly and specifically activated by cAMP is found in Drosophila larval muscle. At least three cAMP molecules are involved in the opening reaction. Half-maximal effect is obtained at about 50 microM. This channel is blocked by micromolar amount of tetraethylammonium applied internally. Interestingly, this channel has a probability of opening 10-20-fold larger in the mutant dunce, a mutant that possesses abnormally elevated intracellular cAMP level, than in the wild type.
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Affiliation(s)
- R Latorre
- Centro de Estudios Cientificos de Santiago, Chile
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29
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Gorczyca MG, Wu CF. Single-channel K+ currents in Drosophila muscle and their pharmacological block. J Membr Biol 1991; 121:237-48. [PMID: 1865488 DOI: 10.1007/bf01951557] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Four types of nonvoltage-activated potassium channels in the body-wall muscles of Drosophila third instar larvae have been identified by the patch-clamp technique. Using the inside-out configuration, tetraethylammonium (TEA), Ba2+, and quinidine were applied to the cytoplasmic face of muscle membranes during steady-state channel activation. The four channels could be readily distinguished on the basis of their pharmacological sensitivities and physiological properties. The KST channel was the only type that was activated by stretch. It had a high unitary conductance (100 pS in symmetrical 130/130 mM KCl solution), was blocked by TEA (Kd approximately 35 mM), and was the most sensitive to Ba2+ (complete block at 10(-4) M). A Ca(2+)-activated potassium channel, KCF.72 pS (130/130) mM KCl), was gated open at greater than 10(-8) m Ca2+, was the least sensitive to Ba2+ Kd of approximately 3 mM) and TEA (Kd of approximately 100 mM), and was not affected by quinidine. K2 was a small conductance channel of 11 pS (130/2 KCl, pipette/bath), and was very sensitive to quinidine, being substantially blocked at 0.1 mM. It also exhibited a half block at approximately 0.3 mM Ba2+ and approximately 25 mM TEA. A fourth channel type, K3, was the most sensitive to TEA (half block less than 1 mM). It displayed a partial block to Ba2+ at 10 mM, but no block by 0.1 mM quinidine. The blocking effects of TEA, Ba2+ and quinidine were reversible in all channels studied. The actions of TEA and Ba2+ appeared qualitatively different: in all four channels, TEA reduced the apparent unitary conductance, whereas Ba2+ decreased channel open probability.
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Affiliation(s)
- M G Gorczyca
- Department of Biology, University of Iowa, Iowa City 52242
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30
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Families of potassium channel genes in mammals: Toward an understanding of the molecular basis of potassium channel diversity. Mol Cell Neurosci 1991; 2:89-102. [DOI: 10.1016/1044-7431(91)90001-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/1991] [Indexed: 11/22/2022] Open
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Chapter 10 Potassium Channels in Developing Excitable Cells. CURRENT TOPICS IN MEMBRANES 1991. [DOI: 10.1016/s0070-2161(08)60808-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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32
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Abstract
Potassium channels are a diverse group of ion channels present in most eukaryotic cells that have been examined. Over 30 different potassium channels have been characterized biophysically. They show different sensitivities to voltage and/or intracellular messengers, and have different kinetic or pharmacological properties. The wide range of potassium channel properties reflects the broad spectrum of cellular functions that they serve, including control of synaptic efficacy, of heart beat, and of endocrine and exocrine secretion. How might this tremendous diversity of potassium channels be generated? Partial answers have begun to emerge as molecular studies of potassium channel genes have become possible over the past few years.
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Affiliation(s)
- L Y Jan
- Howard Hughes Medical Institute, University of California, San Francisco 94143
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