Cronkite D L, Pierce S K
Biology Department, Hope College, Holland, Michigan 49423.
J Exp Zool. 1989 Sep;251(3):275-84. doi: 10.1002/jez.1402510303.
Paramecium calkinsi was isolated from a tidal marsh in which the salinity fluctuated widely on a daily basis. In the laboratory, this ciliate survived for days in sea water ranging in osmotic strength from 10 to 2,000 mOsm and divided in nutritive media of 1,000 mOsm or less. When transferred from 750 to 250 mOsm, cells swelled but regained 78% of the original volume within 60 min and the original volume within 1 day. Cells acclimated to 250 mOsm and transferred to 750 mOsm shrank, regained 40% of the original volume in 60 min, and regained little more volume during the next 24 hr. Free amino acids (FAA), principally proline and alanine, are osmolytes in P. calkinsi. In cells that have been acclimated for more than 1 month, Pro is undetectable at 10 mOsm but at 250 mOsm is present in substantial amounts and is still higher at 750 mOsm. Ala is found in cells at all three salinities and increases dramatically with increasing salinity. A complex pattern of amino acid changes occurs during the 4 hr following a transfer from 250 to 750 mOsm, resulting in a marked increase in Ala but no change in Pro. Thus the metabolic changes that lead to the increased FAA levels of acclimated cells are apparently long-term and complex. After transfer of cells from 750 to 250 mOsm there is a rapid and selective loss of Pro and Ala from the cells to the medium.
卡尔金斯草履虫是从一个潮汐沼泽中分离出来的，在这个沼泽中，盐度每天都有很大波动。在实验室里，这种纤毛虫在渗透强度为10至2000毫渗量的海水中存活了数天，并在1000毫渗量或更低的营养培养基中分裂。当从750毫渗量转移到250毫渗量时，细胞会膨胀，但在60分钟内恢复到原来体积的78%，并在1天内恢复到原来体积。适应了250毫渗量并转移到750毫渗量的细胞会收缩，在60分钟内恢复到原来体积的40%，并在接下来的24小时内恢复的体积很少。游离氨基酸（FAA），主要是脯氨酸和丙氨酸，是卡尔金斯草履虫中的渗透调节物质。在适应了1个月以上的细胞中，在10毫渗量时检测不到脯氨酸，但在250毫渗量时大量存在，在750毫渗量时仍然更高。在所有三种盐度的细胞中都发现了丙氨酸，并且随着盐度的增加而急剧增加。从250毫渗量转移到750毫渗量后的4小时内，氨基酸会发生复杂的变化模式，导致丙氨酸显著增加而脯氨酸没有变化。因此，导致适应细胞中游离氨基酸水平增加的代谢变化显然是长期而复杂的。将细胞从750毫渗量转移到250毫渗量后，脯氨酸和丙氨酸会迅速且有选择性地从细胞中流失到培养基中。
