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Numata T, Sato-Numata K, Yoshino M. Intermediate conductance Ca 2+-activated potassium channels are activated by functional coupling with stretch-activated nonselective cation channels in cricket myocytes. FRONTIERS IN INSECT SCIENCE 2023; 2:1100671. [PMID: 38468799 PMCID: PMC10926553 DOI: 10.3389/finsc.2022.1100671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 12/20/2022] [Indexed: 03/13/2024]
Abstract
Cooperative gating of localized ion channels ranges from fine-tuning excitation-contraction coupling in muscle cells to controlling pace-making activity in the heart. Membrane deformation resulting from muscle contraction activates stretch-activated (SA) cation channels. The subsequent Ca2+ influx activates spatially localized Ca2+-sensitive K+ channels to fine-tune spontaneous muscle contraction. To characterize endogenously expressed intermediate conductance Ca2+-activated potassium (IK) channels and assess the functional relevance of the extracellular Ca2+ source leading to IK channel activity, we performed patch-clamp techniques on cricket oviduct myocytes and recorded single-channel data. In this study, we first investigated the identification of IK channels that could be distinguished from endogenously expressed large-conductance Ca2+-activated potassium (BK) channels by adding extracellular Ba2+. The single-channel conductance of the IK channel was 62 pS, and its activity increased with increasing intracellular Ca2+ concentration but was not voltage-dependent. These results indicated that IK channels are endogenously expressed in cricket oviduct myocytes. Second, the Ca2+ influx pathway that activates the IK channel was investigated. The absence of extracellular Ca2+ or the presence of Gd3+ abolished the activity of IK channels. Finally, we investigated the proximity between SA and IK channels. The removal of extracellular Ca2+, administration of Ca2+ to the microscopic region in a pipette, and application of membrane stretching stimulation increased SA channel activity, followed by IK channel activity. Membrane stretch-induced SA and IK channel activity were positively correlated. However, the emergence of IK channel activity and its increase in response to membrane mechanical stretch was not observed without Ca2+ in the pipette. These results strongly suggest that IK channels are endogenously expressed in cricket oviduct myocytes and that IK channel activity is regulated by neighboring SA channel activity. In conclusion, functional coupling between SA and IK channels may underlie the molecular basis of spontaneous rhythmic contractions.
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Affiliation(s)
- Tomohiro Numata
- Department of Integrative Physiology, Graduate School of Medicine, Akita University, Akita, Japan
- Department of Biology, Tokyo Gakugei University, Tokyo, Japan
| | - Kaori Sato-Numata
- Department of Integrative Physiology, Graduate School of Medicine, Akita University, Akita, Japan
- Department of Biology, Tokyo Gakugei University, Tokyo, Japan
| | - Masami Yoshino
- Department of Biology, Tokyo Gakugei University, Tokyo, Japan
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Maldonado-Díaz C, Vazquez M, Marie B. A comparison of three different methods of eliciting rapid activity-dependent synaptic plasticity at the Drosophila NMJ. PLoS One 2021; 16:e0260553. [PMID: 34847197 PMCID: PMC8631638 DOI: 10.1371/journal.pone.0260553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 11/11/2021] [Indexed: 11/29/2022] Open
Abstract
The Drosophila NMJ is a system of choice for investigating the mechanisms underlying the structural and functional modifications evoked during activity-dependent synaptic plasticity. Because fly genetics allows considerable versatility, many strategies can be employed to elicit this activity. Here, we compare three different stimulation methods for eliciting activity-dependent changes in structure and function at the Drosophila NMJ. We find that the method using patterned stimulations driven by a K+-rich solution creates robust structural modifications but reduces muscle viability, as assessed by resting potential and membrane resistance. We argue that, using this method, electrophysiological studies that consider the frequency of events, rather than their amplitude, are the only reliable studies. We contrast these results with the expression of CsChrimson channels and red-light stimulation at the NMJ, as well as with the expression of TRPA channels and temperature stimulation. With both these methods we observed reliable modifications of synaptic structures and consistent changes in electrophysiological properties. Indeed, we observed a rapid appearance of immature boutons that lack postsynaptic differentiation, and a potentiation of spontaneous neurotransmission frequency. Surprisingly, a patterned application of temperature changes alone is sufficient to provoke both structural and functional plasticity. In this context, temperature-dependent TRPA channel activation induces additional structural plasticity but no further increase in the frequency of spontaneous neurotransmission, suggesting an uncoupling of these mechanisms.
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Affiliation(s)
- Carolina Maldonado-Díaz
- Institute of Neurobiology, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
- Department of Anatomy & Neurobiology, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
| | - Mariam Vazquez
- Institute of Neurobiology, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
| | - Bruno Marie
- Institute of Neurobiology, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
- Department of Anatomy & Neurobiology, University of Puerto Rico, Medical Sciences Campus, San Juan, Puerto Rico
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Lnenicka GA. Crayfish and Drosophila NMJs. Neurosci Lett 2020; 732:135110. [PMID: 32497734 DOI: 10.1016/j.neulet.2020.135110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 05/27/2020] [Accepted: 05/29/2020] [Indexed: 01/06/2023]
Abstract
Many synaptic studies have utilized the experimental advantages of the Arthropod NMJ and the most prominent preparations have been the crayfish and Drosophila larval NMJs. Early cellular studies in the crayfish established the framework for later molecular studies in Drosophila. The two neuromuscular systems are compared including the advantages presented by each preparation for cellular analysis. Beginning with the early work in the crayfish, research developments are followed in the areas of structure/function relationships, activity-dependent synaptic plasticity/development and synaptic homeostasis. A reoccurring theme in these studies is the regulation of active zone structure and function. Early studies in the crayfish focused on the role of active zone number/size and possible functional heterogeneity in regulating transmitter release. Recent studies in Drosophila have begun to characterize this heterogeneity using new approaches that combine imaging of transmitter release, Ca2+ influx and molecular composition for individual active zones.
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Affiliation(s)
- Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, United States.
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Walcott KCE, Mauthner SE, Tsubouchi A, Robertson J, Tracey WD. The Drosophila Small Conductance Calcium-Activated Potassium Channel Negatively Regulates Nociception. Cell Rep 2019; 24:3125-3132.e3. [PMID: 30231996 PMCID: PMC6454897 DOI: 10.1016/j.celrep.2018.08.070] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2014] [Revised: 06/11/2018] [Accepted: 08/23/2018] [Indexed: 12/20/2022] Open
Abstract
Inhibition of nociceptor activity is important for the prevention of spontaneous pain and hyperalgesia. To identify the critical K+ channels that regulate nociceptor excitability, we performed a forward genetic screen using a Drosophila larval nociception paradigm. Knockdown of three K+ channel loci, the small conductance calcium-activated potassium channel (SK), seizure, and tiwaz, causes marked hypersensitive nociception behaviors. In more detailed studies of SK, we found that hypersensitive phenotypes can be recapitulated with a genetically null allele. Optical recordings from nociceptive neurons showed a significant increase in mechanically activated Ca2+ signals in SK mutant nociceptors. SK is expressed in peripheral neurons, including nociceptive neurons. Interestingly, SK proteins localize to axons of these neurons but are not detected in dendrites. Our findings suggest a major role for SK channels in the regulation of nociceptor excitation and are inconsistent with the hypothesis that the important site of action is within dendrites. Walcott et al. performed a forward genetic screen and identify three potassium channel subunits that negatively regulate nociception in Drosophila larvae. In a more detailed investigation of the SK channel, null mutants, rescue experiments, optical recordings, and protein localization studies indicate a functional role for SK in nociceptor excitability.
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Affiliation(s)
- Kia C E Walcott
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC, USA
| | - Stephanie E Mauthner
- Gill Center for Biomolecular Research, Indiana University, Bloomington, IN, USA; Department of Biology, Indiana University, Bloomington, IN, USA
| | - Asako Tsubouchi
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Jessica Robertson
- Department of Cell Biology, Duke University Medical Center, Durham, NC, USA
| | - W Daniel Tracey
- Gill Center for Biomolecular Research, Indiana University, Bloomington, IN, USA; Department of Biology, Indiana University, Bloomington, IN, USA; Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA; Department of Cell Biology, Duke University Medical Center, Durham, NC, USA.
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He T, Nitabach MN, Lnenicka GA. Parvalbumin expression affects synaptic development and physiology at the Drosophila larval NMJ. J Neurogenet 2018; 32:209-220. [PMID: 30175644 DOI: 10.1080/01677063.2018.1498496] [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: 10/28/2022]
Abstract
Presynaptic Ca2+ appears to play multiple roles in synaptic development and physiology. We examined the effect of buffering presynaptic Ca2+ by expressing parvalbumin (PV) in Drosophila neurons, which do not normally express PV. The studies were performed on the identified Ib terminal that innervates muscle fiber 5. The volume-averaged, residual Ca2+ resulting from single action potentials (APs) and AP trains was measured using the fluorescent Ca2+ indicator, OGB-1. PV reduced the amplitude and decay time constant (τ) for single-AP Ca2+ transients. For AP trains, there was a reduction in the rate of rise and decay of [Ca2+]i but the plateau [Ca2+]i was not affected. Electrophysiological recordings from muscle fiber 5 showed a reduction in paired-pulse facilitation, particularly the F1 component; this was likely due to the reduction in residual Ca2+. These synapses also showed reduced synaptic enhancement during AP trains, presumably due to less buildup of synaptic facilitation. The transmitter release for single APs was increased for the PV-expressing terminals and this may have been a homeostatic response to the decrease in facilitation. Confocal microscopy was used to examine the structure of the motor terminals and PV expression resulted in smaller motor terminals with fewer synaptic boutons and active zones. This result supports earlier proposals that increased AP activity promotes motor terminal growth through increases in presynaptic [Ca2+]i.
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Affiliation(s)
- Tao He
- a Division of Pulmonary and Critical Care Medicine , David Geffen School of Medicine at UCLA , Los Angeles , CA , USA
| | - Michael N Nitabach
- b Department of Cellular and Molecular Physiology , Yale School of Medicine , New Haven , CT , USA
| | - Gregory A Lnenicka
- c Department of Biological Sciences , University at Albany , Albany , NY , USA
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Ribchester RR, Slater CR. Rapid retrograde regulation of transmitter release at the NMJ. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.06.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Powers AS, Grizzaffi J, Lnenicka GA. Increased postsynaptic Ca
2+
reduces mini frequency at the
Drosophila
larval NMJ. Synapse 2017; 71. [DOI: 10.1002/syn.21971] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2016] [Revised: 02/14/2017] [Accepted: 02/26/2017] [Indexed: 01/02/2023]
Affiliation(s)
- Andrew S. Powers
- Department of Biological SciencesUniversity at Albany SUNYAlbany New York12222
| | - Jeffrey Grizzaffi
- Department of Biological SciencesUniversity at Albany SUNYAlbany New York12222
| | - Gregory A. Lnenicka
- Department of Biological SciencesUniversity at Albany SUNYAlbany New York12222
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Regulation of quantal currents determines synaptic strength at neuromuscular synapses in larval Drosophila. Pflugers Arch 2016; 468:2031-2040. [PMID: 27783155 DOI: 10.1007/s00424-016-1893-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 10/09/2016] [Accepted: 10/11/2016] [Indexed: 10/20/2022]
Abstract
Studies of synaptic homeostasis during muscle fiber (MF) growth in Drosophila larvae have focused on the regulation of the quantal content of transmitter release. However, early studies in crayfish and frog suggested that regulation of quantal current size may be an integral mechanism in synaptic homeostasis. To examine this further in Drosophila, we compared the electrical properties, miniature excitatory postsynaptic potentials (minEPSPs) and miniature excitatory postsynaptic currents (minEPSCs) in different-sized MFs in third-instar larvae and for a single MF during larval growth. The third-instar MFs showed differences in input resistance due to differences in size and specific membrane resistance. We found that electrical coupling between MFs did not contribute substantially to the electrical properties; however, the electrode leak conductance and a slower developing increase in membrane conductance can influence the electrical recordings from these MFs. Our results demonstrated that larger MFs had larger minEPSCs to compensate for changes in MF electrical properties. This was most clearly seen for MF4 during larval growth from the second to third instar. During a predicted 80 % decrease in MF input resistance, the minEPSCs showed a 35 % increase in amplitude and 165 % increase in duration. Simulations demonstrated that the increase in minEPSC size resulted in a 129 % increase in minEPSP amplitude for third-instar larvae; this was mainly due to the increase in minEPSC duration. We also found that MFs with common innervation had similar-sized minEPSCs suggesting that MF innervation influences minEPSC size. Overall, the results showed that increased quantal content and quantal current size contribute equally to synaptic homeostasis during MF growth.
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Ueda A, Wu CF. The role of cAMP in synaptic homeostasis in response to environmental temperature challenges and hyperexcitability mutations. Front Cell Neurosci 2015; 9:10. [PMID: 25698925 PMCID: PMC4313691 DOI: 10.3389/fncel.2015.00010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 01/08/2015] [Indexed: 11/13/2022] Open
Abstract
Homeostasis is the ability of physiological systems to regain functional balance following environment or experimental insults and synaptic homeostasis has been demonstrated in various species following genetic or pharmacological disruptions. Among environmental challenges, homeostatic responses to temperature extremes are critical to animal survival under natural conditions. We previously reported that axon terminal arborization in Drosophila larval neuromuscular junctions (NMJs) is enhanced at elevated temperatures; however, the amplitude of excitatory junctional potentials (EJPs) remains unaltered despite the increase in synaptic bouton numbers. Here we determine the cellular basis of this homeostatic adjustment in larvae reared at high temperature (HT, 29°C). We found that synaptic current focally recorded from individual synaptic boutons was unaffected by rearing temperature (<15°C to >30°C). However, HT rearing decreased the quantal size (amplitude of spontaneous miniature EJPs, or mEJPs), which compensates for the increased number of synaptic releasing sites to retain a normal EJP size. The quantal size decrease is accounted for by a decrease in input resistance of the postsynaptic muscle fiber, indicating an increase in membrane area that matches the synaptic growth at HT. Interestingly, a mutation in rutabaga (rut) encoding adenylyl cyclase (AC) exhibited no obvious changes in quantal size or input resistance of postsynaptic muscle cells after HT rearing, suggesting an important role for rut AC in temperature-induced synaptic homeostasis in Drosophila. This extends our previous finding of rut-dependent synaptic homeostasis in hyperexcitable mutants, e.g., slowpoke (slo). In slo larvae, the lack of BK channel function is partially ameliorated by upregulation of presynaptic Shaker (Sh) IA current to limit excessive transmitter release in addition to postsynaptic glutamate receptor recomposition that reduces the quantal size.
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Affiliation(s)
- Atsushi Ueda
- Department of Biology, University of Iowa Iowa City, IA, USA
| | - Chun-Fang Wu
- Department of Biology, University of Iowa Iowa City, IA, USA
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