. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IONIC CONTROL OF METAMORPHOSIS 127. Figure 1. Larval attachment in response to GABA in MBL sea water. GABA was added at 10"^ A/(A), 10"* M (9). 4 X 10^ A/(A), and 0 A/(0). Data are averages of duplicates, with standard deviations indicated by vertical bars. Ion excess effects Increased external potassium effectively induced larval attachment, whether added as sulfate or chloride salts to MBL sea water, or used as a replacement for either Na* or Mg^^ (Fig. 2). In the paired response curves, K^ added with CI" wa
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IONIC CONTROL OF METAMORPHOSIS 127. Figure 1. Larval attachment in response to GABA in MBL sea water. GABA was added at 10"^ A/(A), 10"* M (9). 4 X 10^ A/(A), and 0 A/(0). Data are averages of duplicates, with standard deviations indicated by vertical bars. Ion excess effects Increased external potassium effectively induced larval attachment, whether added as sulfate or chloride salts to MBL sea water, or used as a replacement for either Na* or Mg^^ (Fig. 2). In the paired response curves, K^ added with CI" was slightly more efficient as an inducer than when added with S04^ . Similarly, the limiting concen- tration of 20 mM KCl was more rapidly toxic than 10 mM K2SO4 (data not included). Both the inductive and toxic effects of K^ were slightly reduced in medium with sulfate present as the paired anion, instead of chloride. Increases in the external concentrations of other sea water cations, added in excess to MBL sea water as CI" and S04^~ salts, were not inductive (Table II). With the exception of increased Ca^^, the presence of the various excess salts did not inhibit larval attachment in response to 4 X 10"' M GABA, indicating that an increase in osmotic pressure alone neither induces nor inhibits induction of metamorphosis. The inhibitory effect of increased Ca^^ on induction by GABA corroborates the results obtained from media in which Ca^^ concentration was increased by the replacement of Mg^^ (as reported below); these results single out Ca'^^, rather than concomitant alterations in the substitute or paired salt ion concentration, as the cause of the inhibitory effect. We have observed that the induction of metamorphosis by excess K^ is comparable in several respects to that observed with GABA. The efficiency of induction is a dose- dependent function, limited at high concentrations by toxicity. The process of induction involves a temporal component; an optimal conc
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