. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 14 U. KOPPELHUS ET AL E c o o tO Q O 0,25 -i 0,20 - 0,15 - 0,10 - 0,05 - 0,00. Control PP 1 mg / ml PP mg / ml PP mg / ml 0 60 Figure 5. Effect of proteose peptone (PP) in different concentrations. PP was tested in final concentration of mg ml ' (•). mg ml"' (•). and 1 mg ml ' (A). Cuvettes containing no attractant were tested as controls (D). hyrnena, during starvation, undergoes a progressive de- crease in cellular density, which in turn may affect the ability of the cells to enter the metrizamide phas
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 14 U. KOPPELHUS ET AL E c o o tO Q O 0,25 -i 0,20 - 0,15 - 0,10 - 0,05 - 0,00. Control PP 1 mg / ml PP mg / ml PP mg / ml 0 60 Figure 5. Effect of proteose peptone (PP) in different concentrations. PP was tested in final concentration of mg ml ' (•). mg ml"' (•). and 1 mg ml ' (A). Cuvettes containing no attractant were tested as controls (D). hyrnena, during starvation, undergoes a progressive de- crease in cellular density, which in turn may affect the ability of the cells to enter the metrizamide phase. The metrizamide phase itself is known to reduce the swimming speed of the cells slightly (Hellung-Larsen el ai, 1986). The progressive decrease in swimming speed and cell vol- ume known to take place during starvation might also offer some explanation of the observed phenomenon (Hellung-Larsen cl ai. 1993). During continued starvation, sensitivity to most at- tractants is gradually lost according to the relative strengths of the chemoattractants. It is remarkable, however, that sensitivity to PP was never lost. In addition to being a chemoattractant, PP is known to increase the swimming speed of the cells (Hellung-Larsen el ai. 1986). The stim- ulation by PP of the swimming speed may in part explain the strong chemosensory responses induced by this che- moattractant. The results confirm that amino acids and peptides are chemoattractants for Tetrahymena. The responses to a mixture of amino acids were strong in comparison to the responses obtained using single amino acids. This additive effect may indicate a mechanism in which the amino acids work through specific receptors. Specific receptors may also explain the additive effect seen when AA mix + PDGF are tested in the assay. We have confirmed the chemoattractive effect of PDGF, FGF, 0-endorphin, and acetylcholine shown ear- lier (Tsang and Levandowsky, 1983; Andersen el ai. 1984; Leick and Hellung-Larsen. 1985; Hellung-
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