GEORC'.K T. SCOTT AND HUGH R. HAYWOOD 6l 



ral)l)it kidney slices in whiili the lurnover of polassium as measured with K^- 

 was not affected by variation in extracellular sodium concentration from 78- 

 234 mEq/ liter. The interpretation of our data is consistent with his ilndings. 



Recent studies were carried out in relation to an observed variation in the 

 potassium content of Ulva collected from the brackish water of Perch Pond, 

 near Falmouth, j\Iassachusetts, the salinity of which was found to be from 65 

 to 70% that of ocean water. Ulva from this source contained significantly less 

 potassium than material from the Eel Pond in Woods Hole, where the salinity 

 is closer to that of ocean water. 



Accordingly, the following experiment was performed: sea water was diluted 

 to 70% with distilled water, and calcium, magnesium, sulfate, and bicarbonate 

 ions were restored to full strength according to Allen's formula for artificial 

 sea water (i). Four solutions were prepared from this as follows: a) no additions; 

 b) K(l added to restore normal K content of sea water; c) NaCl added to 

 restore normal Na content of sea water; d) both K and Na restored to normal. 



Table 7. .\lter.a,tion of cellular c.vriONS as a response to changes in environmental 



SODIUM AND POTASSIUM 



'70% S.W.' denotes the dilution of sea water by 30% with distilled water and the addition 

 of salts of CaCb. MgCb, MgSOi, and NaHCOs to the full natural concentrations. In (6) 

 K+ was restored to normal concentration (9.73 mEq/1.), in (c) Na+ was restored (423 niEq/l.), 

 and in {d) both salts were added. The time was 15 hr. and the samples were maintained in the 

 dark {Ulva). 



Thus ic) and {d) have essentially the same osmotic pressure, whereas the os- 

 motic pressures of {a) and (b) are approximately 30% lower. The potassium 

 contents of fronds in (c) and (d) were observed to be higher than those of 

 (c) and {b) (table 7). Since the percentage dry weights of samples from all four 

 solutions w^ere constant, the potassium increment in (c) and {d) cannot be the 

 result of a concentration by water loss. Apparently the cell has adjusted its 

 potassium concentration with respect to the change in external salinity in 

 order to maintain osmotic regulation. In the previous section in which potas- 

 sium accumulation w^as shown to be independent of external sodium concen- 

 tration in artilicial sea water, osmotic pressure was maintained constant by the 

 addition of sucrose. In both cases, therefore, one major function of intracellular 

 potassium is to contribute to the internal osmotic pressure. 



DISCUSSION 



Concerning the experiments on Ulva, the most tenable interpretation of the 

 data presented is that mechanisms are operative in Ulva for the accumulation 



