demonstrated by the effect on a receptor heart of fluid which had been 

 perfused from a stimulated donor heart. An electrical response to ACh is 

 shown by changes in the electrocardiograph. These changes were interpreted 

 as changes in conduction velocity of 2 propagated monophasic components of 

 opposite sign. The ACh-blocking agent tetraethylammonium bromide was shown 

 to antagonize anodal effects and augment cathodal effects in clam heart. 

 These interactions between electrical and chemical aspects of beating of 

 Venus heart suggested that the ACh system is intimately associated with 

 electrical aspects of excitation. - J.L.M. 



1986 



Welsh, John H.,and Rae Taub. 1948. 



The action of choline and related compounds on the heart of Venus mereenaria. 

 Biol. Bull. 95(3): 346-353. 



Isolated heart of V. mereenaria is unusually sensitive to acetylcholine (ACh) , 

 in certain respects superior to dorsal muscle of leech, rectus abdominis of 

 frog, isolated frog heart, and blood pressure of cat. Hard clam is usually 

 available in the market. Under refrigeration it remains edible for some 

 weeks, but after 1 to 2 wks the heart beats irregularly. Experimental 

 material, therefore, should be fresh. Shell length of 8 to 12 cm is the most 

 convenient size. The heart is exposed by removing umbo and hinge of shells 

 and cutting away mantle and precardium dorsal to the heart. Threads for 

 attaching to a support in the bath and to a writing lever are passed under 

 the atria and tied close to the ventricle. The ventricle is isolated by 

 cutting atria distal to the threads .and cutting blood vessels and intestine. 

 Although only the outer surface of the heart is directly exposed to materials 

 introduced to the batch, cannulation and introduction of ACh into the 

 ventricle does not increase sensitivity. Fluids in the bath must be changed 

 without draining the bath. A bath capacity of 10 ml is appropriate. Sea- 

 water is an adequate perfusion fluid, which maintains a regular beat for 2 to 

 3 days. Artificial seawater made from 30 g NaCl, 0.9 g KC1, 1.1 g CaCl2/ 

 and 3.5 g MgS04.3H20 in 1 liter of water, buffered to pH 7-7.5 with phosphate 

 or bicarbonate is satisfactory. Oxygen supply should be gentle to avoid 

 disturbance. Although treatment with an anti-cholinesterase potentiates the 

 action of ACh 2 to 5 times, this is normally undesirable because hard clam 

 heart is so sensitive to ACh and recovery after ACh treatment is slowed by 

 anti-cholinesterase. Hearts which fail to beat or beat with low amplitude 

 can be excited with adrenaline or tyramine, but the effect is abolished 

 quickly by washing. Ergot alkaloids, like ergotoxine, ergotamine, and 

 ergonovine have remarkably persistent excitatory action. Venus heart is 

 smooth muscle, with pharmacology not unlike that of some vertebrate smooth 

 muscles. Sensitivity of Venus heart is greatest in late winter and spring, 

 but the seasonal change is not great. In late summer the beat tends to be 

 irregular. ACh sometimes, at low concentrations (10~H to 10~10 M) , induces 

 a small increase in amplitude. At 10-9 to 10~8 the effect is negative, and 

 at a concentration of about 50 times that which just gives a measurable 

 decrease in amplitude the heart stops in diastole. The log-concentration- 

 response curve is sigmoid. Ten compounds related to choline or ACh were much 

 less effective in inhibiting hard clam heart action than Ach. Triethylcholine 

 chloride and triethylacetyl choline iodide caused no inhibition. - J.L.M. 



1987 



Welsh, J. H., and R. Taub. 1948. 



The action of choline and related compounds on the heart of Venus mereenaria.. 

 Biol. Bull. 95: 618-630. 



Volume 95 of Biol. Bull, has no pages 618-630. A paper of the same title, by 

 the same authors, appears on pages 346-353 of Biol. Bull. Vo. 95. The two 

 were cited in the same paper, but the second reference was either an error, 

 or appeared in another journal. (See p. 220 of Vergleichende Pharmakologie 

 von Ubertragersubstanzen in tierssystematischer Darstellung, by Hans Fischer. 

 In Handbuch der experimentellen Pharmakologie, Band 26, Springer-Verlag 

 Berlin, Heidelberg, New York, 1971.) - J.L.M. 



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