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Biol Bull 137: 161-169. (August 1969)
© 1969 Marine Biological Laboratory
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OSMOREGULATION IN A MARINE CILIATE, MIAMIENSIS AVIDUS. II. REGULATION OF INTRACELLUAR FREE AMINO ACIDS

E. S. KANESHIRO 1, G. G. HOLZ JR. 1, and P. B. DUNHAM 1

1 Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. The total free amino acid concentration in Miamiensis avidus in 100% sea water is 317 mM/kg cells. Alanine, glycine and proline account for 73% of the total.

2. Reducing the external osmolarity resulted in a decrease in intracellular free amino acids; raising the external osmolarity resulted in an increase in free amino acids. At the extreme salinities tested, cells in 25% sea water contained 24% of the free amino acids of cells in 100% sea water; cells in 200% sea water had a 22% greater free amino acid content than cells in 100% sea water. All of the changes were complete 20 minutes after the salinity changes.

3. The intracellular free amino acid content was a function of external osmolarity, and not ionic strength or concentration of individual ions.

4. The mechanism of the increase in free amino acid content was mobilization of bound amino acids, and not uptake from the medium.

5. These results, together with earlier findings on regulation of ions and water in Miamiensis avidus, suggest that this organism maintains itself hyperosmotic to its environment over a wide range of external salinities. The functional significance of the hyperosmotic state may be to obtain water to operate the contractile vacuole. The possibility of a fresh water ancestry for marine ciliates is discussed.




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