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 rosettaAmrit 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/Im

ax

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.