Antillatoxin is a sodium channel activator that displays unique efficacy in heterologously expressed rNav1.2, rNav1.4 and rNav1.5 alpha subunits

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Antillatoxin (ATX) is a structurally unique lipopeptide produced by the marine cyanobacterium<jats:italic>Lyngbya majuscula</jats:italic>. ATX activates voltage-gated sodium channel α-subunits at an undefined recognition site and stimulates sodium influx in neurons. However, the pharmacological properties and selectivity of ATX on the sodium channel α-subunits were not fully characterized.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>In this study, we characterized the pharmacological properties and selectivity of ATX in cells heterologously expressing rNa<jats:sub>v</jats:sub>1.2, rNa<jats:sub>v</jats:sub>1.4 or rNa<jats:sub>v</jats:sub>1.5 α-subunits by using the Na<jats:sup>+</jats:sup>selective fluorescent dye, sodium-binding benzofuran isophthalate. ATX produced sodium influx in cells expressing each sodium channel α-subunit, whereas two other sodium channel activators, veratridine and brevetoxin-2, were without effect. The ATX potency at rNa<jats:sub>v</jats:sub>1.2, rNa<jats:sub>v</jats:sub>1.4 and rNa<jats:sub>v</jats:sub>1.5 did not differ significantly. Similarly, there were no significant differences in the efficacy for ATX-induced sodium influx between rNa<jats:sub>v</jats:sub>1.2, rNa<jats:sub>v</jats:sub>1.4 and rNa<jats:sub>v</jats:sub>1.5 α-subunits. ATX also produced robust Ca<jats:sup>2+</jats:sup>influx relative to other sodium channel activators in the calcium-permeable DEAA mutant of rNa<jats:sub>v</jats:sub>1.4 α-subunit. Finally, we demonstrated that the 8-demethyl-8,9-dihydro-antillatoxin analog was less efficacious and less potent in stimulating sodium influx.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>ATX displayed a unique efficacy with respect to stimulation of sodium influx in cells expressing rNa<jats:sub>v</jats:sub>1.2, rNa<jats:sub>v</jats:sub>1.4 and rNa<jats:sub>v</jats:sub>1.5 α-subunits. The efficacy of ATX was distinctive inasmuch as it was not shared by activators of neurotoxin sites 2 and 5 on VGSC α-subunits. Given the unique pharmacological properties of ATX interaction with sodium channel α-subunits, decoding the molecular determinants and mechanism of action of antillatoxin may provide further insight into sodium channel gating mechanisms.</jats:p></jats:sec>