INTAKE AND LOSS OF IONS BY LIVING CELLS. I. EGGS AND LARVAE OF ARBACIA PUNCTULATA AND ASTERIAS FORBESI EXPOSED TO PHOSPHATE AND SODIUM IONS

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Abstract
(1) Eggs and larvae of Arbacia punctulata and Asterias forbesi were immersed in sea water containing low concentrations of radioactive sodium phosphate (0.175-0.81 mM) and the phosphate content in subsequently collected samples after intervals up to 48 hours was determined by measuring the β-radiation from the samples. It was found that: a) Phosphate was taken in often in at least two distinct periods, the first within the first half hour, followed by a loss of the ion, and secondly in the later stages. b) The permeabilities during early absorption are generally greater than those during late absorption. c) If it be assumed that the only driving force is the concentration gradient across the plasma membrane (a very imperfect assumption), the early permeabilities vary from 5,3 to 96 x 10–6 moles cm–2 hr–1 (GM L–1)–1 for Arbacia and 2280 x 10–6 for Asterias. The late permeabilities of both range from 2.2 to 426 x 10–6. d) The maximum concentrations found in eggs or larvae of both vary from 0.050 to 8.3 mM for Arbacia, and 0.35 to 0.48 mM for Asterias. (2) Inverse correlations are intimated between external concentration or radioactivity and permeability. The effects of radiation are discussed. (3) The part played by the stage of the egg or larva, the effect of the methods used, the dimensions of ions, and theories of absorption are discussed.

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