. Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954. Electrophysiology; Electrolytes; Electrolytes; Electrophysiology; Physiology, Comparative. EMANUEL EPSTEIN 107 The initial rapid uptake and its reversal are interpreted as due to non- metabolic cation exchange in which the root acts as a solid exchanger, like clays or synthetic exchange resins. The slower linear phase of uptake is considered to represent absorption proper, in the sense of active transport. Evidence for the n
. Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954. Electrophysiology; Electrolytes; Electrolytes; Electrophysiology; Physiology, Comparative. EMANUEL EPSTEIN 107 The initial rapid uptake and its reversal are interpreted as due to non- metabolic cation exchange in which the root acts as a solid exchanger, like clays or synthetic exchange resins. The slower linear phase of uptake is considered to represent absorption proper, in the sense of active transport. Evidence for the non-metabolic exchange character of the fast process is as follows: i) The time-course of this phase is that typical of exchange reactions, and an equilib- rium is quickly approached. 2) The Sr* taken up by this mechanism is ex- changeable with Sr, Ca, Mg, Na, K, and H ions, and the relative effectiveness of the divalent and monovalent ions in displacing Sr* from the roots suggests the lyotropic series which is common in exchange reactions on solid exchangers, j) Whereas the relatively slow, steady-state phase of absorption is abolished Fig. 4. Double reciprocal plot of interference by Ca and Mg with Sr absorption by excised barley roots. Sr concentration (S), to mEq/1. Rate of Sr absorp- tion, V, in fresh weight/3 ^S. by anaerobic conditions, the same is not true of the fast, initial exchange re- action. In order to determine the rate of the metabolic absorption of Sr* unobscured by the additional exchange increment, we let the roots absorb Sr* under the given experimental conditions, and then 'stripped off' the non-metabolically held, exchangeable Sr* by means of a 30-minute exposure to non-radioactive Sr. In this manner, we measured only the non-exchangeable fraction, the fraction that had been absorbed as distinguished from the exchangeably ad- sorbed Sr* fraction. Measured in this way, absorption was found to be a linear function of time and a s
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