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A fast Na+/Ca2+-based action potential in a marine diatom.

Taylor AR - PLoS ONE (2009)

Bottom Line: Underpinning many of these electrical signals is a fast Na+-based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals.The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles.The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists.

View Article: PubMed Central - PubMed

Affiliation: The Marine Biological Association of the UK, Citadel Hill, Plymouth, United Kingdom. taylora@uncw.edu

ABSTRACT

Background: Electrical impulses in animals play essential roles in co-ordinating an array of physiological functions including movement, secretion, environmental sensing and development. Underpinning many of these electrical signals is a fast Na+-based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals. Such rapid action potentials are thought to have evolved with the first metazoans, with cnidarians being the earliest representatives. The present study demonstrates that a unicellular protist, the marine diatom Odontella sinensis, can also generate a fast Na+/Ca2+ based action potential that has remarkably similar biophysical and pharmacological properties to invertebrates and vertebrate cardiac and skeletal muscle cells.

Methodology/principal findings: The kinetic, ionic and pharmacological properties of the rapid diatom action potential were examined using single electrode current and voltage clamp techniques. Overall, the characteristics of the fast diatom currents most closely resemble those of vertebrate and invertebrate muscle Na+/Ca2+ currents.

Conclusions/significance: This is the first demonstration of voltage-activated Na+ channels and the capacity to generate fast Na+-based action potentials in a unicellular photosynthetic organism. The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles. The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists.

Show MeSH
Pore regions and selectivity motifs of animal and diatom voltage activated Na+ and Ca2+ channels.ClustalW was used to perform multiple sequence alignment of the 4 ‘P’ loop domains of animal and diatom voltage activated Na+/Ca2+ channels. The selectivity motifs for each pore domain are indicated by boxes with conserved residues conferring selectivity indicated by asterisk. All 4 residues that contribute to the selectivity filter are indicated [34]. Protein sequences were obtained from NCBI and accession numbers are indicated. The diatom sequence for the putative 4 domain voltage activated Na+ permeable channel was obtained through a BLAST search of the Thalassioira pseudonana genome, Protein ID 2207, http://genome.jgi-psf.org/Thaps3/Thaps3.home.html.
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pone-0004966-g005: Pore regions and selectivity motifs of animal and diatom voltage activated Na+ and Ca2+ channels.ClustalW was used to perform multiple sequence alignment of the 4 ‘P’ loop domains of animal and diatom voltage activated Na+/Ca2+ channels. The selectivity motifs for each pore domain are indicated by boxes with conserved residues conferring selectivity indicated by asterisk. All 4 residues that contribute to the selectivity filter are indicated [34]. Protein sequences were obtained from NCBI and accession numbers are indicated. The diatom sequence for the putative 4 domain voltage activated Na+ permeable channel was obtained through a BLAST search of the Thalassioira pseudonana genome, Protein ID 2207, http://genome.jgi-psf.org/Thaps3/Thaps3.home.html.

Mentions: The biophysical and pharmacological properties of the diatom Na+ current are remarkably similar to those of invertebrates and of vertebrate cardiac muscle. The question then arises as to the presence of a gene or genes in diatoms that can code functional voltage activated Na+ channels with the characteristics observed in this study. The α subunit of animal Na+ channels is a large 4-domain membrane spanning protein [17], [18], which may have originated from the single domain bacterial Na+ channel [19]. Each of the four domains consists of six transmembrane units designated S1–6. Voltage sensing and gating is achieved by positive charged arginine residues in the S4 units. Voltage dependent inactivation of Na+ channels is determined by a highly conserved IMFT motif of the domain III–IV linker of the α subunit [18], [20] and the channel selectivity is determined by the so called ‘P’ loop of S5–S6 linker. Using a range of vertebrate and invertebrate Na+ channel amino acid sequences, a BLAST search was conducted on the genome sequence of the related marine diatom T. pseudonana [12]. One voltage-activated channel gene with high homology with both the invertebrate Na+ channel and vertebrate Na+ and Ca2+ channel α subunits was found to be present [21]. The predicted amino acid sequence of this gene codes for 4 domains of six membrane spanning units each of which includes both the voltage sensing S4 motifs and the P loops between S5 and S6 as described above. Interestingly, this predicted diatom 4-domain voltage-activated channel exhibits conserved P-loop motif of 4 conserved glutamate residues that result in a selectivity filter that is more alike those described for animal voltage gated Ca2+ channels (Figure 5). Overall the putative diatom channel has the predicted structure and function that is consistent with all of the biophysical characteristics described here. This gene and homologues in O.sinensis are thus promising candidates for molecular characterisation of the ion channels underpinning diatom membrane excitability and signalling.


A fast Na+/Ca2+-based action potential in a marine diatom.

Taylor AR - PLoS ONE (2009)

Pore regions and selectivity motifs of animal and diatom voltage activated Na+ and Ca2+ channels.ClustalW was used to perform multiple sequence alignment of the 4 ‘P’ loop domains of animal and diatom voltage activated Na+/Ca2+ channels. The selectivity motifs for each pore domain are indicated by boxes with conserved residues conferring selectivity indicated by asterisk. All 4 residues that contribute to the selectivity filter are indicated [34]. Protein sequences were obtained from NCBI and accession numbers are indicated. The diatom sequence for the putative 4 domain voltage activated Na+ permeable channel was obtained through a BLAST search of the Thalassioira pseudonana genome, Protein ID 2207, http://genome.jgi-psf.org/Thaps3/Thaps3.home.html.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2654917&req=5

pone-0004966-g005: Pore regions and selectivity motifs of animal and diatom voltage activated Na+ and Ca2+ channels.ClustalW was used to perform multiple sequence alignment of the 4 ‘P’ loop domains of animal and diatom voltage activated Na+/Ca2+ channels. The selectivity motifs for each pore domain are indicated by boxes with conserved residues conferring selectivity indicated by asterisk. All 4 residues that contribute to the selectivity filter are indicated [34]. Protein sequences were obtained from NCBI and accession numbers are indicated. The diatom sequence for the putative 4 domain voltage activated Na+ permeable channel was obtained through a BLAST search of the Thalassioira pseudonana genome, Protein ID 2207, http://genome.jgi-psf.org/Thaps3/Thaps3.home.html.
Mentions: The biophysical and pharmacological properties of the diatom Na+ current are remarkably similar to those of invertebrates and of vertebrate cardiac muscle. The question then arises as to the presence of a gene or genes in diatoms that can code functional voltage activated Na+ channels with the characteristics observed in this study. The α subunit of animal Na+ channels is a large 4-domain membrane spanning protein [17], [18], which may have originated from the single domain bacterial Na+ channel [19]. Each of the four domains consists of six transmembrane units designated S1–6. Voltage sensing and gating is achieved by positive charged arginine residues in the S4 units. Voltage dependent inactivation of Na+ channels is determined by a highly conserved IMFT motif of the domain III–IV linker of the α subunit [18], [20] and the channel selectivity is determined by the so called ‘P’ loop of S5–S6 linker. Using a range of vertebrate and invertebrate Na+ channel amino acid sequences, a BLAST search was conducted on the genome sequence of the related marine diatom T. pseudonana [12]. One voltage-activated channel gene with high homology with both the invertebrate Na+ channel and vertebrate Na+ and Ca2+ channel α subunits was found to be present [21]. The predicted amino acid sequence of this gene codes for 4 domains of six membrane spanning units each of which includes both the voltage sensing S4 motifs and the P loops between S5 and S6 as described above. Interestingly, this predicted diatom 4-domain voltage-activated channel exhibits conserved P-loop motif of 4 conserved glutamate residues that result in a selectivity filter that is more alike those described for animal voltage gated Ca2+ channels (Figure 5). Overall the putative diatom channel has the predicted structure and function that is consistent with all of the biophysical characteristics described here. This gene and homologues in O.sinensis are thus promising candidates for molecular characterisation of the ion channels underpinning diatom membrane excitability and signalling.

Bottom Line: Underpinning many of these electrical signals is a fast Na+-based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals.The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles.The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists.

View Article: PubMed Central - PubMed

Affiliation: The Marine Biological Association of the UK, Citadel Hill, Plymouth, United Kingdom. taylora@uncw.edu

ABSTRACT

Background: Electrical impulses in animals play essential roles in co-ordinating an array of physiological functions including movement, secretion, environmental sensing and development. Underpinning many of these electrical signals is a fast Na+-based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals. Such rapid action potentials are thought to have evolved with the first metazoans, with cnidarians being the earliest representatives. The present study demonstrates that a unicellular protist, the marine diatom Odontella sinensis, can also generate a fast Na+/Ca2+ based action potential that has remarkably similar biophysical and pharmacological properties to invertebrates and vertebrate cardiac and skeletal muscle cells.

Methodology/principal findings: The kinetic, ionic and pharmacological properties of the rapid diatom action potential were examined using single electrode current and voltage clamp techniques. Overall, the characteristics of the fast diatom currents most closely resemble those of vertebrate and invertebrate muscle Na+/Ca2+ currents.

Conclusions/significance: This is the first demonstration of voltage-activated Na+ channels and the capacity to generate fast Na+-based action potentials in a unicellular photosynthetic organism. The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles. The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists.

Show MeSH