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Elliott ER, Brock KE, Vacassenno RM, Harrison DA, Cooper RL. The effects of doxapram and its potential interactions with K2P channels in experimental model preparations. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2024; 210:869-884. [PMID: 38802613 DOI: 10.1007/s00359-024-01705-6] [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: 02/05/2024] [Revised: 05/15/2024] [Accepted: 05/18/2024] [Indexed: 05/29/2024]
Abstract
The channels commonly responsible for maintaining cell resting membrane potentials are referred to as K2P (two-P-domain K+ subunit) channels. These K+ ion channels generally remain open but can be modulated by their local environment. These channels are classified based on pharmacology, pH sensitivity, mechanical stretch, and ionic permeability. Little is known about the physiological nature of these K2P channels in invertebrates. Acidic conditions depolarize neurons and muscle fibers, which may be caused by K2P channels given that one subtype can be blocked by acidic conditions. Doxapram is used clinically as a respiratory aid known to block acid-sensitive K2P channels; thus, the effects of doxapram on the muscle fibers and synaptic transmission in larval Drosophila and crawfish were monitored. A dose-dependent response was observed via depolarization of the larval Drosophila muscle and an increase in evoked synaptic transmission, but doxapram blocked the production of action potentials in the crawfish motor neuron and had a minor effect on the resting membrane potential of the crawfish muscle. This indicates that the nerve and muscle tissues in larval Drosophila and crawfish likely express different K2P channel subtypes. Since these organisms serve as physiological models for neurobiology and physiology, it would be of interest to further investigate what types of K2P channel are expressed in these tissues. (212 words).
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Affiliation(s)
- Elizabeth R Elliott
- Department of Biology, University of Kentucky, Lexington, KY, 40506-0225, USA
| | - Kaitlyn E Brock
- Department of Biology, University of Kentucky, Lexington, KY, 40506-0225, USA
| | | | - Douglas A Harrison
- Department of Biology, University of Kentucky, Lexington, KY, 40506-0225, USA
| | - Robin L Cooper
- Department of Biology, University of Kentucky, Lexington, KY, 40506-0225, USA.
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Brock KE, Elliott ER, Taul AC, Asadipooya A, Bocook D, Burnette T, Chauhan IV, Chhadh B, Crane R, Glover A, Griffith J, Hudson JA, Kashif H, Nwadialo SO, Neely DM, Nukic A, Patel DR, Ruschman GL, Sales JC, Yarbrough T, Cooper RL. The Effects of Lithium on Proprioceptive Sensory Function and Nerve Conduction. NEUROSCI 2023; 4:280-295. [PMID: 39484179 PMCID: PMC11523691 DOI: 10.3390/neurosci4040023] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 10/15/2023] [Accepted: 10/18/2023] [Indexed: 11/03/2024] Open
Abstract
Animals are exposed to lithium (Li+) in the natural environment as well as by contact with industrial sources and therapeutic treatments. Low levels of exposure over time and high volumes of acute levels can be harmful and even toxic. The following study examines the effect of high-volume acute levels of Li+ on sensory nerve function and nerve conduction. A proprioceptive nerve in the limbs of a marine crab (Callinectes sapidus) was used as a model to address the effects on stretch-activated channels (SACs) and evoked nerve conduction. The substitution of Li+ for Na+ in the bathing saline slowed nerve conduction rapidly; however, several minutes were required before the SACs in sensory endings were affected. The evoked compound action potential slowed in conduction and slightly decreased in amplitude, while the frequency of nerve activity with joint movement and chordotonal organ stretching significantly decreased. Both altered responses could be partially restored with the return of a Na+-containing saline. Long-term exposure to Li+ may alter the function of SACs in organisms related to proprioception and nerve conduction, but it remains to be investigated.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Robin L. Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA
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Elliott ER, Brock KE, Taul AC, Asadipooya A, Bocook D, Burnette T, Chauhan IV, Chhadh B, Crane R, Glover A, Griffith J, Hudson JA, Kashif H, Nwadialo SO, Neely DM, Nukic A, Patel DR, Ruschman GL, Sales JC, Yarbrough T, Cooper RL. The Effects of Zinc on Proprioceptive Sensory Function and Nerve Conduction. NEUROSCI 2023; 4:305-318. [PMID: 39484175 PMCID: PMC11523716 DOI: 10.3390/neurosci4040025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 11/01/2023] [Accepted: 11/07/2023] [Indexed: 11/03/2024] Open
Abstract
Zinc (Zn2+) is an essential element that can promote proper organ function, cell growth, and immune response; it can also, however, be present in too great a quantity. Zinc toxicity caused by overexposure may result in both minor and major physiological effects, with chronic exposure at low levels and acute exposure at high levels being harmful or even toxic. This investigation examines the effects of acute exposure to relatively high concentrations of Zn2+ on sensory nerve function and nerve conduction. A proprioceptive nerve in marine crab (Callinectes sapidus) limbs was used as a model to assess the effects of Zn2+ on stretch-activated channels (SACs) and evoked nerve conduction. Exposure to Zn2+ slowed nerve condition rapidly; however, several minutes were required before the SACs in sensory endings were affected. A depression in conduction speed and an increase followed by a decrease in amplitude were observed for the evoked compound action potential, while the frequency of nerve activity upon joint movement and stretching of the chordotonal organ significantly decreased. These altered responses could be partially reversed via extensive flushing with fresh saline to remove the zinc. This indicates that subtle, long-term exposure to Zn2+ may alter an organism's SAC function for channels related to proprioception and nerve conduction.
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Affiliation(s)
- Elizabeth R Elliott
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Kaitlyn E Brock
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Alaina C Taul
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Artin Asadipooya
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Devin Bocook
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Tessa Burnette
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Isha V Chauhan
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Bilal Chhadh
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Ryan Crane
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Ashley Glover
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Joshua Griffith
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - JayLa A Hudson
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Hassan Kashif
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Samuel O Nwadialo
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Devan M Neely
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Adel Nukic
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Deep R Patel
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Gretchen L Ruschman
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Johnathan C Sales
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Terra Yarbrough
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
| | - Robin L Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA; (E.R.E.); (K.E.B.); (A.C.T.); (A.A.); (D.B.); (T.B.); (I.V.C.); (B.C.); (R.C.); (A.G.); (J.G.); (J.A.H.); (H.K.); (S.O.N.); (D.M.N.); (A.N.); (D.R.P.); (G.L.R.); (J.C.S.); (T.Y.)
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Ison BJ, Abul-Khoudoud MO, Ahmed S, Alhamdani AW, Ashley C, Bidros PC, Bledsoe CO, Bolton KE, Capili JG, Henning JN, Moon M, Phe P, Stonecipher SB, Tanner HN, Turner LT, Taylor IN, Wagers ML, West AK, Cooper RL. The Effect of Doxapram on Proprioceptive Neurons: Invertebrate Model. NEUROSCI 2022; 3:566-588. [PMID: 39483770 PMCID: PMC11523696 DOI: 10.3390/neurosci3040041] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 10/20/2022] [Indexed: 11/03/2024] Open
Abstract
The resting membrane potential enables neurons to rapidly initiate and conduct electrical signals. K2p channels are key in maintaining this membrane potential and electrical excitability. They direct the resting membrane potential toward the K+ equilibrium potential. Doxapram is a known blocker for a subset of K2p channels that are pH sensitive. We assessed the effects of 0.1 and 5 mM doxapram on the neural activity within the propodite-dactylopodite (PD) proprioceptive sensory organ in the walking legs of blue crabs (Callinectes sapidus). Results indicate that 0.1 mM doxapram enhances excitation, while the higher concentration 5 mM may over-excite the neurons and promote a sustained absolute refractory period until the compound is removed. The effect of 5 mM doxapram mimics the effect of 40 mM K+ exposure. Verapamil, another known K2p channel blocker as well as an L-type Ca2+ channel blocker, reduces neural activity at both 0.1 and 5 mM. Verapamil may block stretch activated channels in sensory endings, in addition to reducing the amplitude of the compound action potential with whole nerve preparations. These findings are notable as they demonstrate that doxapram has acute effects on neurons of crustaceans, suggesting a targeted K2p channel. The actions of verapamil are complex due to the potential of affecting multiple ion channels in this preparation. Crustacean neurons can aid in understanding the mechanisms of action of various pharmacological agents as more information is gained.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Robin L. Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
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5
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Pankau C, Nadolski J, Tanner H, Cryer C, Di Girolamo J, Haddad C, Lanning M, Miller M, Neely D, Wilson R, Whittinghill B, Cooper RL. Examining the effect of manganese on physiological processes: Invertebrate models. Comp Biochem Physiol C Toxicol Pharmacol 2022; 251:109209. [PMID: 34628058 PMCID: PMC8922992 DOI: 10.1016/j.cbpc.2021.109209] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 09/24/2021] [Accepted: 10/03/2021] [Indexed: 01/03/2023]
Abstract
Manganese (Mn2+ as MnSO4 &/or MnCl2) is a common and essential element for maintaining life in plants and animals and is found in soil, fresh waters and marine waters; however, over exposure is toxic to organisms. MnSO4 is added to soil for agricultural purposes and people are exposed to Mn2+ in the mining industry. Hypermanganesemia in mammals is associated with neurological issues mimicking Parkinson's disease (PD) and appears to target dopaminergic neural circuits. However, it also seems that hypermanganesemia can affect many aspects of health besides dopaminergic synapses. We examined the effect on development, behavior, survival, cardiac function, and glutamatergic synaptic transmission in the Drosophila melanogaster. In addition, we examined the effect of Mn2+ on a sensory proprioceptive organ and nerve conduction in a marine crustacean and synaptic transmission at glutamatergic neuromuscular junctions of freshwater crayfish. A dose-response effect of higher Mn2+ retards development, survival and cardiac function in larval Drosophila and survival in larvae and adults. MnSO4 as well as MnCl2 blocks stretch activated responses in primary proprioceptive neurons in a dose-response manner. Mn2+ blocks glutamatergic synaptic transmission in Drosophila as well as crayfish via presynaptic action. This study is relevant in demonstrating the effects of Mn2+ on various physiological functions in order to learn more about acute and long-term consequences Mn2+ exposure.
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Affiliation(s)
- Cecilia Pankau
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Jeremy Nadolski
- Department of Mathematical and Computational Sciences, Benedictine University, Lisle, IL 60532, USA
| | - Hannah Tanner
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA; Department of Biology, Eastern Kentucky University, Richmond, KY 40475, USA
| | - Carlie Cryer
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - John Di Girolamo
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Christine Haddad
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Matthew Lanning
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Mason Miller
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Devan Neely
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Reece Wilson
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | | | - Robin L Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA.
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Potter R, Meade A, Potter S, Cooper RL. Rapid and Direct Action of Lipopolysaccharide (LPS) on Skeletal Muscle of Larval Drosophila. BIOLOGY 2021; 10:1235. [PMID: 34943150 PMCID: PMC8698716 DOI: 10.3390/biology10121235] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 11/21/2021] [Accepted: 11/24/2021] [Indexed: 02/02/2023]
Abstract
The endotoxin lipopolysaccharide (LPS) from Gram-negative bacteria exerts a direct and rapid effect on tissues. While most attention is given to the downstream actions of the immune system in response to LPS, this study focuses on the direct actions of LPS on skeletal muscle in Drosophila melanogaster. It was noted in earlier studies that the membrane potential rapidly hyperpolarizes in a dose-dependent manner with exposure to LPS from Pseudomonas aeruginosa and Serratia marcescens. The response is transitory while exposed to LPS, and the effect does not appear to be due to calcium-activated potassium channels, activated nitric oxide synthase (NOS), or the opening of Cl- channels. The purpose of this study was to further investigate the mechanism of the hyperpolarization of the larval Drosophila muscle due to exposure of LPS using several different experimental paradigms. It appears this response is unlikely related to activation of the Na-K pump or Ca2+ influx. The unknown activation of a K+ efflux could be responsible. This will be an important factor to consider in treatments of bacterial septicemia and cellular energy demands.
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Affiliation(s)
- Rachel Potter
- College of Medicine, University of Kentucky, 800 Rose Street MN 150, Lexington, KY 40506, USA; (R.P.); (S.P.)
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA;
| | - Alexis Meade
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA;
| | - Samuel Potter
- College of Medicine, University of Kentucky, 800 Rose Street MN 150, Lexington, KY 40506, USA; (R.P.); (S.P.)
| | - Robin L. Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA;
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The Effect of Calcium Ions on Mechanosensation and Neuronal Activity in Proprioceptive Neurons. NEUROSCI 2021. [DOI: 10.3390/neurosci2040026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Proprioception of all animals is important in being able to have coordinated locomotion. Stretch activated ion channels (SACs) transduce the mechanical force into electrical signals in the proprioceptive sensory endings. The types of SACs vary among sensory neurons in animals as defined by pharmacological, physiological and molecular identification. The chordotonal organs within insects and crustaceans offer a unique ability to investigate proprioceptive function. The effects of the extracellular environment on neuronal activity, as well as the function of associated SACs are easily accessible and viable in minimal saline for ease in experimentation. The effect of extracellular [Ca2+] on membrane properties which affect voltage-sensitivity of ion channels, threshold of action potentials and SACs can be readily addressed in the chordotonal organ in crab limbs. It is of interest to understand how low extracellular [Ca2+] enhances neural activity considering the SACs in the sensory endings could possibly be Ca2+ channels and that all neural activity is blocked with Mn2+. It is suggested that axonal excitability might be affected independent from the SAC activity due to potential presence of calcium activated potassium channels (K(Ca)) and the ability of Ca2+ to block voltage gated Na+ channels in the axons. Separating the role of Ca2+ on the function of the SACs and the excitability of the axons in the nerves associated with chordotonal organs is addressed. These experiments may aid in understanding the mechanisms of neuronal hyperexcitability during hypocalcemia within mammals.
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