Meeting Abstract

140-7  Sunday, Jan. 7 15:00 – 15:15  Characterization of Na⁺ channel homologs from two marine phytoplankton KOESTER, JA*; HELLIWELL, KE; TAYLOR, AR; University of North Carolina Wilmington; Marine Biological Association, Plymouth, UK koesterj@uncw.edu

Four domain voltage-gated Na⁺ and Ca²⁺ channels mediate rapid physiological responses in metazoans. Fast Na⁺ and Ca²⁺-based action potentials likely evolved in single celled organisms before the evolution of multicellular neuromuscular systems, although their functional role is not well understood. We recently discovered that fast action potentials in some marine phytoplankton may be underpinned by homologs of single domain bacterial Na⁺ channels (NavBac), suggesting a unique role of these proteins in unicellular eukaryotes. We therefore heterologously expressed two NavBac homologs, one from the diatom Odontella sinsensis and one from the coccolithophore Scyphosphaera apsteinii in the mammalian cell line HEK293. Whole cell patch clamp analysis revealed that the expressed proteins from both species mediate fast activating, rapidly inactivating inward currents in response to depolarization. Both channels exhibited steady state inactivation with recovery from inactivation. The coccolithophore protein exhibited much faster activation and inactivation kinetics (τ_act=0.62 ms ± 0.40, τ_inact=1.16ms ± 0.34) compared to the diatom protein (τ_act=1.18 ms ± 0.53, τ_inact=46.90ms ± 8.50). These kinetic features are similar to the properties of four-domain voltage-gated Na⁺ channels in animals, implying the single-domain proteins tetramerize to form a functional voltage gated channel. Differentiation in the amino acids of the selectivity filter suggests that the coccolithophore channel selects for Na⁺ over Ca²⁺, while the diatom channel is permeant to Ca²⁺. Our data suggest unique functional roles for single-domain voltage-gated Na⁺ and Ca²⁺ channels among the diverse lineages of marine protists.