Determination of Na channel blockers in paralytic shellfish toxins and pufferfish toxins with a tissue biosensor.

The biosensor consisted of a sodium electrode and covered with the frog bladder membrane within a flow cell was tested for the estimation of tetrodotoxin (TTX) and saxitoxin (STX). This sensor was applied to detect very low amounts of the Na+ channel blockers, STX and TTX, in different shellfishes and swellfishes. A good agreement was obtained between TTX activities determined by mouse assay and amounts of Na+ channel blockers estimated by frog membrane sensor. The lowest level of TTX (fg) that can be determined by frog membrane sensor does not cause human poisoning. The channel blockers in short-necked clam, which was assumed to be STX, were monitored by this sensor continuously every week for one year. It was discovered that the STX content increased from July until September and then decreased from October until March. The biosensor proposed here may be used for the estimation of STX and TTX conventionally in the future.