Just like people, clams can be affected by the toxins that cause paralytic shellfish poisoning (PSP), but scientists have now identified a mutation in clams that gives some protection. PSP toxins interfere with nerve function, and the mutation, which changes a single amino acid in a sodium channel, makes nerves less sensitive to those toxins.

The discovery is reported in the April 7 issue of the journal Nature. The authors suggest that it has wide ranging implications for the evolution of shellfish in the presence of toxic algae and increases the risk of PSP to people who eat clams by enabling contaminated clams to survive in the presence of toxins.

The report, "Sodium channel mutation leading to saxitoxin resistance in clams increases risk of PSP," was written by a team of scientists, including Laurie Connell of the University of Maine School of Marine Sciences. It describes differences in the responses of two soft shell clam populations -- one in the Bay of Fundy and the other in the Lawrencetown estuary in Nova Scotia -- to saxitoxin as well as tetrodotoxin, a powerful toxin derived from the puffer fish.

The lead author is V. Monica Bricelj of the Institute for Marine Biosciences in Halifax, Nova Scotia, and in addition to Connell, co-authors are Keiichi Konoki, Todd Scheuer, and William A. Catterall of the University of Washington; Scott P. MacQuarrie of the Institute for Marine Biosciences; and Vera L. Trainer of the National Oceanic and Atmospheric Administration in Seattle.

"Since the 1960s, it's been known that different species of shellfish have different resistance to PSP toxins," says Connell. "This is the first time the source of that resistance has been shown. We now have a marker that can be used to determine if clams have this mutation. It's easy to use and could help reduce the time of clam flat closures (related to red tide)."

Betty Twarog, a neurophysiologist who works at UMaine's Darling Marine Center in Walpole, Main
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Contact: Laurie Connell
laurie.connell@umit.maine.edu
207-581-2470
University of Maine
6-Apr-2005

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