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

Background: Antillatoxin (ATX) is a structurally unique lipopeptide produced by the marine cyanobacterium Lyngbya majuscula. ATX activates voltage-gated sodium channel alpha-subunits at an undefined recognition site and stimulates sodium influx in neurons. However, the pharmacological properties and selectivity of ATX on the sodium channel a-subunits were not fully characterized. Results: In this study, we characterized the pharmacological properties and selectivity of ATX in cells heterologously expressing rNa(v)1.2, rNa(v)1.4 or rNa(v)1.5 alpha-subunits by using the Na+ selective fluorescent dye, sodium-binding benzofuran isophthalate. ATX produced sodium influx in cells expressing each sodium channel alpha-subunit, whereas two other sodium channel activators, veratridine and brevetoxin-2, were without effect. The ATX potency at rNa(v)1.2, rNa(v)1.4 and rNa(v)1.5 did not differ significantly. Similarly, there were no significant differences in the efficacy for ATX-induced sodium influx between rNa(v)1.2, rNa(v)1.4 and rNa(v)1.5 alpha-subunits. ATX also produced robust Ca2+ influx relative to other sodium channel activators in the calcium-permeable DEAA mutant of rNa(v)1.4 alpha-subunit. Finally, we demonstrated that the 8-demethyl-8,9-dihydro-antillatoxin analog was less efficacious and less potent in stimulating sodium influx. Conclusions: ATX displayed a unique efficacy with respect to stimulation of sodium influx in cells expressing rNa(v)1.2, rNa(v)1.4 and rNa(v)1.5 alpha-subunits. The efficacy of ATX was distinctive inasmuch as it was not shared by activators of neurotoxin sites 2 and 5 on VGSC alpha-subunits. Given the unique pharmacological properties of ATX interaction with sodium channel alpha-subunits, decoding the molecular determinants and mechanism of action of antillatoxin may provide further insight into sodium channel gating mechanisms.