SroCav1 is a highly calcium selective channel in Salpingoeca rosetta that lacks calcium-dependent inactivation. It does not allow sodium passage. SroNav2 is a non-selective channel that allows equal passage of calcium and sodium ions, as shown by a doubling of inward current when sodium is introduced. The document examines the origins and properties of voltage-gated sodium and calcium channels in the primitive single-celled eukaryote S. rosetta to understand their potential roles in signaling and movement.

1. Figure 4. Relative inward ion permeability. (A) SroCav1 relative permeability to Na+ (left)
and Ba2+ (right). SroCav1 appears to be a highly calcium selective channel. It appears to
lack calcium-dependent inactivation as evidenced by channel kinetics when barium is
substituted for calcium as the primary extracellular ion and charge carrier.
(B) SroNav2 relative permeability to Na+ (left) and Ba2+ (right). SroNav2 appears to be a
non-selective channel as evidenced by a near doubling of inward current size when sodium
is introduced to experimental environment and allowed to pass through the channel, likely a
consequence of its DEEA selectivity filter. Unlike SroCav1, barium currents of SroNav2 are
significantly smaller than calcium currents.
Origins of voltage-gated sodium and calcium channels in primordial single-celled eukaryote Salpingoeca rosetta
Amrit Mehta and J. David Spafford1
1Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
Here we show the isolated complement of gene homologs from
the simplest extant eukaryotic species, Salpingoeca rosetta, to
possess voltage-gated sodium (Na+) and calcium (Ca2+)
channels. The structurally similar to Nav1, SroNav2, passes
both calcium and sodium ions equally, while SroCav1 is highly
calcium selective and does not allow the passage of sodium
ions. We are interested in evaluating the non-selective nature
of SroNav2 and highly conserved nature of SroCav1, and to
understand the roles both SroNav2 and SroCav1 may play in
Salpingoeca.
Figure 1. Phylogenetic analysis and distribution based
on voltage-gated ion channel genes with maximum-
likelihood scores. Moran and Zakon. (2014)
Bendahhou, A., Cummins, T.R., Tawil, R., Waxman, S.G., Ptacek, L.J. J.Neurosci. 19(12) (1999) 4762-4771
Moran, Y., Zakon, H., Gen. Biol. Evol. 6(9) (2014) 2210-2217
Acknowledgements
3
2
1 Figure 2. Representative current
traces of SroCav1 and SroNav2.
(A, left) Current trace of SroNav1
inward current in 2mM [Ca2+]ex.
(A, Right) Contrasting current
trace of Nav1.4 (SCN4A).
Bendahhou et al., (1999)
(B) Current trace of SroCav1
inward current in 20mM [Ca2+]ex
A
-80 -60 -40 -20 0 20 40
1.0
0.8
0.6
0.4
0.2
0.0
I/Imax
V (mV)
B
B
Ca2+
Ca2+
Na+
Ba2+
A
Ca2+
Na+
Ca2+
Ba2+
B
4
We predict that these homologs of voltage-gated Ca2+ and Na+ channels found in single cell
choanoflagellate Salpingoeca rosetta may generate Ca2+-dependent action potentials that
signal between cells of choanoflagellate colonies, regulate intra-cellular events, or control
movement of it’s single flagellum or cilia.
Planned experiments include performing patch-clamp and/or microelectrode recordings
directly on Salpingoeca rosetta, to allow assessment of these ionic currents in their native
environment, testing drug sensitivity common calcium and sodium channel blockers.
Conclusions
References
Introduction
A
Figure 3. Current-voltage relationship of SroCav1 (left) and SroNav2
(right). Both channels are maximally activated at membrane potentials near
0mV.