2114 



Elliott, Ellen J. 1979. 



Cholinergic response in the heart of the clam Mercenaria mercenaria: 

 Activation by Conus californicus venom component. J. Comp. Physiol. 129(1): 

 61-66. 



The spontaneously beating heart of M. mercenaria is inhibited by an extract 

 from the venom of the marine snail C. californicus . This inhibition is 

 antagonized by benzoquinonium, tetraethylammonium, phenyltrimethylammonium, 

 and methylxylocholine, all of which antagonize cholinergic inhibition of 

 Mercenaria heart, and is not blocked by d-tubocurarine, hexamethonium, atro- 

 pine, or a-bungarotoxin. In addition, cholinergic inhibition of Mercenaria 

 heart is mimicked by arecoline, blocked by methylxylocholine and phenyltri- 

 methylammonium, and not significantly affected by hexamethonium or a- 

 bungarotoxin. It is proposed that the Conus venom agent inhibits Mercenaria 

 heart by activation of the cholinergic response of the heart. It is also 

 concluded that the cholinergic response in Mercenaria heart is pharmacolog- 

 ically identical to the slow, potassium-mediated hyperpolarizing cholinergic 

 response found on Aplysia neurons. - modified author's summary - J.L.M. 



2115 



Elliott, Ellen J. 1980. 



Three types of acetylcholine response in bivalve heart muscle cells. 

 J. Physiol. 300: 283-302. 



Acetylcholine (ACh) responses of cardiac muscle cells from 3 species of bi- 

 valve, Mercenaria mercenaria, Mytilus edulis, and Crassostrea virginica, 

 were studied by intracellular recording and ACh ionophoresis. Heart muscle 

 contraction was abolished by bathing in artificial seawater in which Mn 2+ 

 had been substituted for Ca -+ . A slow hyperpolarization was observed in the 

 clam, a rapid depolarization which was sometimes followed by a slower hyper- 

 polarization in the mussel, and a biphasic response consisting of a rapid 

 depolarization and slower hyperpolarization in the oyster. All responses 

 were accompanied by an increase in membrane conductance, as measured by 

 passing constant current pulses with an extracellular suction electrode. 

 The hyperpolarizing response was blocked most effectively by methylxylocho- 

 line and not very effectively by tubocurarine or hexamethonium. The hyper- 

 polarizing response was not altered by CI -free or Na + -free seawater, but 

 was affected by changes in external K*. The rate of change of the inversion 

 potential of this response with change in (K + ) was 59 mv per tenfold con- 

 centration change. The 3 types of ACh response seen in bivalve heart muscles 

 were similar with respect to time course, pharmacological sensitivity, and 

 ionic mechanism to the 3 types 'of ACh response described in Aplysia central 

 neurones. Analogies also can be drawn with vertebrate ACh responses. - modi- 

 field author's summary - J.L.M. 



2116 



Elliott, Ellen J., and Michael A. Raftery. 1979. 



Venom of marine snail Conus californicus : Biochemical studies of a cholino- 

 mimetic component. Toxicon 17(3): 259-268. 



The component responsible for cholinomimetic effects of the fractionated 

 venom of C. californicus on Mercenaria mercenaria heart has not yet been 

 identified. Its structure will be of particular interest to and may prove 

 useful in, the study of the type of ACh response found in Mercenaria heart 

 elicited by the Conus cholinomimetic. This type of ACh response is not 

 effectively blocked by curare or atropine and in general does not correspond 

 pharmacologically to any of the cholinergic responses found in vertebrates. 

 The cholinomimetic is a low molecular weight, positively charged alkaloid 

 compound. Its role in the venom of C. californicus is not known. It may 

 simply be a metabolite, or it is possible that, as a small, positively 

 charged molecule, it functions in intracellular osmoregulation and ion 

 balance. - J.L.M. 



588 



