SESSION SUMMARY PHARMACOLOGY SessionChairperson BettyTwarog TuftsUniversity Medford, Massachusetts Co-Chairman Edward Gilfil lan BigelowLaboratory for OceanSciences McKown Point WestBoothbay Harbor, Maine 7his sess«in served to bring t<igether w«rkers interested tn the pharin.ic<il«gy»fdinoflagellalet<ixjns,not <inly t<i share technical details,but t«i Jentifypr<iblems andexchange information concerning progress inareas of interest<iutside<if their respective specialities.The conference asa wholehas enabledspecialists tobe<urn< acquainted withproblems whichconfront those v'h<imust determine management p<iliciesduring tcixic Jinoflagellate blooms, F<iurrnaj<ir «.insiderati<ins formedtti<basis <ifthe session onpharmacolog.y. I, 4atur«if the Tcixiris and Aspe <if tsT<ixin Release byDinoflayellates Results<itpharmac<il<igi<aI studies <itparalytic shellfish toxinsare consistent withtfi< «n< fusion th.it the prin<.<pal toxicc<imponent ofthe West Coast sp<' Cie+.<inyai<f<t i «it<'n<'11<< issaxi'toxin STX!;while the East Coas't C«nv««krc »rie <ir m<ir» species ci<isely related tciGotiyai< tarnarensis! az c<intatnsa t<ixic prin<.iple inaddition to STX, The toxic components of 'yrnn<i<ftn«mtfiret~rhave n<it yet been well characterized bychemists althoughthepharmac<ilogy israpidly being elucidated. It waspointed outthat tliefragility <ifCyrnn<<Jinii<rrt tosome extent explains thetact that its toxin is releas«lint<i the medium c<intaining theorganism; while toxins of the str<«turally ni<ire r<ibust G<inv<ii<fax speciesare not s<i released, 'lhestudies reported inthis session giverise to further inquiries. It will be necessaryt<iidentity chemically allthe Conyai< laxtoxins, especially the "Conyaulax tantarensis toxin" GLEAM,"Thesame holds forthe Cyirinodiniurn toxins In addi ti<in, one must ask why t he active Gyrnitodirtit<m toxinisfound inculture meVia and in seawater inthe absence ofintact organisms, whilethe Ci<inya«laitoxinis<inly found inassociation withthe organisms orparticulate matter.It may well be that the Gonyaulax toxins are stable only when ads<irbedon particulatematter. II. I:.ffects<>I Toxins on Organisms Mat<ir clinical aspects ofparalytic shellfish poisoning havebeen described in detailin this session; Differences between effects producedby STXand rela ted, uncharactenzedConyat<laz toxin were reported. Clinical implications oftoxic symptoms, both respiratory paralysis andcardiovascular disturbances! were discussed.Fewer details were available concerning the action of thetoxins on l<iwervertebrate animals and on marineinvertebrates, including shellfish. 1'reliminarystudies of theaction of paralyticshellfish toxins on shellfish showedthatfilter feedingdiminished as toxin accumulated. ln thiscategory a number of interestingproblems should be investigated: 9'ork anal yzing the effects ofGartyaulax toxin on shellfish hasonly begun and sh<iuldbe vigorouslypursued. The detailedmode of actionof the Cymnodirtiumtoxins on fish should be carefully worked out since these animalsperish in largenumbers during blooms. Virtual}y no workhas yet beenaccomplished which throws light on the action of Gyrrtnodiitiurrttoxins on marineinvertebrates and such knowledge is needed. Ill. 1<esistanceto Toxins session.TwoaspectsInfish, oftoxinphysiological resistance resistanceisto some toextenttoxin correlatedaction were withdiscussedaccumula intiethis n inthese speciesof a toxinrelated closely in its mode ofaction tvSTX. Th» resistancetoSTX found ina number ofbivalve species is predictive ofth» amountoftoxin which thespecies canaccumulate, andtherefore, itspotential toxicitytoman. To the extent thata shellfish issensitive tothe toxin. itshows symptomsindicatingintoxication, Someshellfish were shown tohave evolved behavioralmechanismswhich protect them from ingesting toxicorganisms. Theresistance totetrodotoxin notedinlower vertebrates mayberelated to theTTX and STX resistance characteristically observedincertain specialized excitablemembranes aswell asin developing musclefibers and in muscle whichhasbeen denervated, Thisresistance totoxins i» not at all well understood,butisclearly related to modification ofphysiological function, ratherthanprotection againstexposure totoxin. Understanding thegeneral mechanismsresponsiblefor resistance maywell shed lighton how resistance evolvedinresponse toexposure totoxins. In shellfish. furtherunderstanding willberequired oftoxic symptoms andtheimplication ofthese symptoms for instance,itwill be useful torecognize symptoms ofpoisoning inbivalves underfield conditions andto be able to estimate theextent oftoxin accumulation.Alsoresistance ofbivalves tnaybe linked notonly torate of uptakeoftoxin, but to rate of detoxification aftera bloom. IV. PhysiologicalandMolecular Basesof the Action ofDtnof4gellate Toxi ns Compellingevidencewas presented thatTTX, STX, and GTTX specifically blockthesodium channels ofthe excitable cellmembrane. thatis. they block thegeneration ofnerve impulses. Inman, lower vertebrates, andin shellfish. thisis the mode ofaction. Within recent years, a component ofnerve membraneshasbeen isolated which appears tobe identical withthe specific bindingsiteof these toxins inthe intact nerve, The mode ofaction o t e Gvrrtrtodirriumtoxinsisless completely known, A hemolytic factoris involved F h and thereis alsoa neurotoxin. Withrespect tothe Gortyaulax toxins, it is clear that considerable progress hasbeen made inelucidating theiractions, Continued studies along the lines alreadyundertaken should bepursued, notonly because investigation ofthe bindingsites of these toxins contributes toknowledge oft e molecular nature of thesodium channel, the basis of all nerve impulses, butalso because knowledgeof the conditionsunder which these toxins bind to nerve membraneswillgive clues as to how to counteract them, both in' he the c inic a conceivablyin fisheries.There have been fewer fundamental studies of Gymrrodiniurrttoxinscompared toGonyaulax, inpart bec toxinshave not yet beenchemically purified and charactermdat the 335 m<ilecularlevel, In viewof thisfact the chemistry and pharmacology of C.yrn»<><fii»«rntoxinsneed to be more intensively investigated, It becameclear during this conference that completestudies of the pharmacol<igyofmany dinof'lagellate toxinshave been recently undertaken. It willbe welc<ime in future conferences to discuss more detailed information fromchemists andpharrnacologists concerning theCyrr<nodirtium toxins,their nature,and their action on man, lower vertebrates, andshellfish. It is hoped thatfar more information willbe available concerning Gonyaufaz species and th»chemistry <ifthe now uncharacterized toxicconstituent called GTTX. It is ali«h<ip»dthatstudies willhave been completed onlower vertebrates and shellfish.I'articularly imp<irtant willbe information relating onone hand to m»<banisrns <>ft<ixin resistance, and<in the other, to the molecular basis of the t<ixicity.These last considerations shouldbe primary foci of attentionat succeedingconferences, SAXITOXIN AND RELATEDPOISONS: THEIRACTIONS ON MAN AND OTHERMAMMALS M. H, Evans Agricultural Research Cc!u ttct l instt ut te ofAnima! Physio logy, Babraham,Cambridge, England. 337 ABSTI AC T Outbreaksntparalytic sht'llfish poisoning alongthe 1'acific coast ofNorth Ameticaappearto be eau~ed bysaxitoxin derived from ~nnvauiai careiiellu Saxitoxincausesparalysis inman and mammals bya specific anddirect action «nnerve and skeletal muscle, inwhich it prevents initiation andpropagation ofaction potentials, byblocking thesodium channels ofthe excitable cell membrane.Theprobably caust.of death isthe failure ofthe movements of respiration.resultingfrom this peripheral paralys~s. Theredoes notappear to beany siy nit icant paralysis of the central nervous system, except in experimentalanimalswhich have hadsaxitoxin administered directlyinto the cerebrospinalParalysisassticiatedfluid, withblooms <ifCi. trtrrtarettsis appearstobe caused bya poisonwhich resembles saxitoxin, though it is notidentical. Large amountsofthis unknown poison were present inthe mussels responsible fora seriiiusoutbreak ofpoisoning alongthe North-East coastof Britain in'1968, lt ciiuldnot be purified bymeans ofthe ion-exchange techniques whichwork efficientlywithsaxitoxin. Itwas partially purified bygel filtration, andfound tii liepharmacologically similarto saxitoxin, It too caused death of experiinentalanimals through a peripheral paralysis of the respiratory mu~les. There were, however, differences between thispoison and saxitoxin in thedetails of s<irneof theireffects on test preparations. IN1 ROD UCTION paralyticshellfish poiscining isa well recognized clinical condition, Halstead inloti& ! listed85 separate outbreaks, between theyears 1689 and 1962, with a totalestimate «1over 959 victims and more than 222 deaths. A morerecent estimatebyI'rakash etat. in 1971 9! putsthe world-wide total at about 1600 t ast.1 h»signs and symptoms thatvictims present toa clinicianhave been des<ribed in detail by Meyer et af. 6!, obeyer5!, Seven4!, Gemmillk h1anderson cih Mc<i!llum et af. 2! andby manyothers. All thec finicalaccounts agree that the first symptom isa paraesthesiawhich isvariiiusly described asa tingling,prickling, stinging orburning sensation. It » firstfelt by the patient in the oral and circumoral areaand soon afterwards appear»nthe fingers and perhaps in thetoes. This first symptom occurs within5 - 30minutes after eating the poisonous bivalves. the speed of onset beingrelated tothe ultimate severity ofthe intoxication. It issoon replaced by a numbnessspreading