Penetration of Radioactive Ions,Their Accumulation by Protoplasm of Living Cells ( Nitella coronata )

Abstract

Exploratory experiments with K∗, Na∗, Rb∗ and Br∗ † reveal hitherto unknown steps of the process of penetration of these ions into living cells. Studies of plant cells with K∗ 1 , 2 , 3 have already shown that it is indispensable to separate the protoplasm from the sap, and to study both of these portions separately. Animal cells lack an obvious vacuole, but experiments with erythrocytes in vivo show that the absorption or removal of ions from the blood as a whole takes place. The amount of ions was deduced from the emission of β particles, using a Geiger-Müller counter and the ratio of the count to the known amount of the radioactive salt used.‡ When K∗Cl is injected in a ca, isotonic solution into a rabbit (which has K rich erythrocytes) the K∗ disappears from the plasma mainly by excretion or absorption, but apparently enters the erythrocytes to approximate diffusion equilibrium but without conspicuous accumulation. When Na∗Cl is injected neither loss from the blood nor accumulation of Na∗ takes place conspicuously. It is hoped that more significant data can be obtained by experiments in vitro.

Earlier experiments with Nitella, show that K∗ does not accumulate to any great extent (i. e., attain concentrations exceeding those of the immersion fluid) in the sap during about the first 10 hours. But during this period we can find pronounced accumulation of ions in the protoplasm, the concentrations being often 10 or 25 times as high in the protoplasm as in the immersion fluid. In this accumulation we can distinguish 3 or 4 phases, shown by K∗: (1) a rapid intake of K∗, usually complete within 1 or 2 hours, which may be an exchange of K∗ from the solution for K from the cell; (2) loss of K∗ from the protoplasm continuing for 2 to 4 hours, and possibly due to the slower entrance of other cations, replacing K∗ and K. This exchange is relatively slow because these ions have other properties (e. g., Na) or a lower concentration (e. g., H) in exchange for the K∗ already taken in. (3) Steady intake of K∗ possibly due to exchange of K∗ from the medium for metabolic products, viz., weak electrolyte cations.