RESUMO
Saxitoxin (STX) and its derivatives are highly toxic natural compounds produced by dinoflagellates commonly present in marine phytoplankton. During algal blooms ("red tides"), shellfish accumulate saxitoxins leading to paralytic shellfish poisoning (PSP) in human consumers. PSP is a consequence of the high-affinity block of voltage-dependent Na channels in neuronal and muscle cells. PSP poses a significant public health threat and an enormous economic challenge to the shellfish industry worldwide. The standard screening method for marine toxins is the mouse mortality bioassay that is ethically problematic, costly and time-consuming. We report here an alternative, functional assay based on electrical recordings in cultured cells stably expressing a PSP target molecule, the STX-sensitive skeletal muscle Na channel. STX-equivalent concentration in the extracts was calibrated by comparison with purified STX, yielding a highly significant correlation (R=0.95; N=30) between electrophysiological determinations and the values obtained by conventional methods. This simple, economical, and reproducible assay obviates the need to sacrifice millions of animals in mandatory paralytic shellfish toxin screening programs.