Date of Award


Document Type


Degree Name

Master of Science




The marsh clam, Rangia cuneata has been shown in other laboratories to maintain body fluid osmolality above that of the medium in salinities below 10 o/oo. Since the membrane bound enzyme Na ++ K+ - ATPase has been implicated in the osmoregulatory processes in many aquatic organisms, the levels of Na++K+-ATPase activity and 3H-ouabain binding in homogenized tissue samples from mantle, gill, rectum, ventricle, kidney, and foot (including epithelial and muscle tissue) were measured. Mantle, kidney, and gill contained substantial concentrations o f Na + +K+ -AT Pase acti. vi. ty an d 3H- ouab ai. n bin d"i ng si. tes. Mantle contained nearly twice the Na++K+-ATPase activity of kidney and more than three times that of gill. Mantle also contained the highest number of binding sites. Turnover numbers calculated for each tissue indicated that mantle pump sites have higher catalytic activity than gill or kidney. Transfer of clams from 10 o/oo to lower salinities resulted in significant increases in Na++K+-ATPase activity in mantle but not in gill. There were no parallel increases in ouabain binding. In clams transferred from 3 o/oo to 0 o/oo, there were no significant changes in mantle Na++K+-ATPase activity until 6 hrs after transfer. Within 12 hrs after transfer, Na++K+-ATPase had increased to equilibrium levels. Kinetic studies indicated that the method of activation does not involve a modification of the affinity of the enzyme + for K .

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