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The ionic dependence of voltage-activated inward currents in the pharyngeal muscle of Caenorhabditis elegans

The ionic dependence of voltage-activated inward currents in the pharyngeal muscle of Caenorhabditis elegans
The ionic dependence of voltage-activated inward currents in the pharyngeal muscle of Caenorhabditis elegans
The pharynx of Caenorhabditis elegans consists of a syncytium of radially orientated muscle cells that contract synchronously and rhythmically to ingest and crush bacteria and pump them into the intestine of the animal. The action potentials that support this activity are superficially similar to vertebrate cardiac action potentials in appearance with a long, calcium-dependent plateau phase. Although the pharyngeal muscle can generate action potentials in the absence of external calcium ions, action potentials are absent when sodium is removed from the extracellullar solution (Franks et al. 2002). Here we have used whole cell patch clamp recordings from the pharynx and show low voltage-activated inward currents that are present in zero external calcium and reduced in zero external sodium ions. Whilst the lack of effect of zero calcium when sodium ions are present is not surprising in view of the known permeability of voltage-gated calcium channels to sodium ions, the reduction in current in zero sodium when calcium ions are present is harder to explain in terms of a conventional voltage-gated calcium channel. Inward currents were also recorded from egl-19 (n582) which has a loss of function mutation in the pharyngeal L-type calcium channel and these were also markedly reduced in zero external sodium. Despite this apparent dependence on external sodium ions, the current was partially blocked by the divalent cations, cadmium, barium and nickel. Using single-channel recordings we identified a cation channel for which the open-time duration was increased by depolarisation. In inside-out patches, the single-channel conductance was highest in symmetrical sodium solution. Further studies are required to determine the contribution of these channels to the pharyngeal action potential.
c. elegans, pharynx, sodium current, calcium current, single channel recording
1354-2516
57-68
Vinogradova, Irina
b3663707-722e-4feb-90ea-ac17ee71aaeb
Cook, Alan
7b75a288-b189-4c85-8122-0f389847ac4a
Holden-Dye, Lindy
8032bf60-5db6-40cb-b71c-ddda9d212c8e
Vinogradova, Irina
b3663707-722e-4feb-90ea-ac17ee71aaeb
Cook, Alan
7b75a288-b189-4c85-8122-0f389847ac4a
Holden-Dye, Lindy
8032bf60-5db6-40cb-b71c-ddda9d212c8e

Vinogradova, Irina, Cook, Alan and Holden-Dye, Lindy (2006) The ionic dependence of voltage-activated inward currents in the pharyngeal muscle of Caenorhabditis elegans. Invertebrate Neuroscience, 6 (2), 57-68. (doi:10.1007/s10158-006-0018-y).

Record type: Article

Abstract

The pharynx of Caenorhabditis elegans consists of a syncytium of radially orientated muscle cells that contract synchronously and rhythmically to ingest and crush bacteria and pump them into the intestine of the animal. The action potentials that support this activity are superficially similar to vertebrate cardiac action potentials in appearance with a long, calcium-dependent plateau phase. Although the pharyngeal muscle can generate action potentials in the absence of external calcium ions, action potentials are absent when sodium is removed from the extracellullar solution (Franks et al. 2002). Here we have used whole cell patch clamp recordings from the pharynx and show low voltage-activated inward currents that are present in zero external calcium and reduced in zero external sodium ions. Whilst the lack of effect of zero calcium when sodium ions are present is not surprising in view of the known permeability of voltage-gated calcium channels to sodium ions, the reduction in current in zero sodium when calcium ions are present is harder to explain in terms of a conventional voltage-gated calcium channel. Inward currents were also recorded from egl-19 (n582) which has a loss of function mutation in the pharyngeal L-type calcium channel and these were also markedly reduced in zero external sodium. Despite this apparent dependence on external sodium ions, the current was partially blocked by the divalent cations, cadmium, barium and nickel. Using single-channel recordings we identified a cation channel for which the open-time duration was increased by depolarisation. In inside-out patches, the single-channel conductance was highest in symmetrical sodium solution. Further studies are required to determine the contribution of these channels to the pharyngeal action potential.

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More information

Published date: 2006
Keywords: c. elegans, pharynx, sodium current, calcium current, single channel recording

Identifiers

Local EPrints ID: 40529
URI: http://eprints.soton.ac.uk/id/eprint/40529
ISSN: 1354-2516
PURE UUID: ffe07c40-c593-446a-9341-6809dd36a552
ORCID for Lindy Holden-Dye: ORCID iD orcid.org/0000-0002-9704-1217

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Date deposited: 04 Jul 2006
Last modified: 09 Jan 2022 02:34

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Author: Irina Vinogradova
Author: Alan Cook

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