Potassium redistribution and water movement in crayfish muscle fibers

Abstract

1. After subjecting the isolated crayfish muscle fiber to a variety of external ionic conditions, the intracellular potassium concentration was measured with an ultramicro integrative flame photometer. 2. The quantity of fiber water was determined by correcting the weight of the fiber for the solid component and the adhering and extracellular water. In normal control Ringer's solution the ratio of fiber water to cell weight is 0.79. 3. The intracellular potassium concentration of a fiber bathed in normal control Ringer was determined as 130±10 mM/kg-H20. With propionate substituted for chloride in the control solution, the final intracellular potassium concentration was 128 ±13 mM/kg-H2O. 4. The muscle fiber was subjected to media made hyperosmotic by the addition of K salts. When the anion was permeant (chloride) the redistribution of the intracellular potassium conformed to a Donnan system. With the impermeant ion propionate, the fiber behaved as an osmometer. 5. When the media were isosmotically changed with the addition of K salts, the fiber potassium did not conform to a Donnan redistribution with chloride, nor as an osmometer with propionate. 6. When the fiber was suddenly exposed to a propionate control solution after equilibration in chloride, the transient time course of intracellular potassium indicated a predominant water movement. This water movement was probably by electroosmosis. After subjecting the isolated crayfish muscle fiber to a variety of external ionic conditions, the intracellular potassium concentration was measured with an ultramicro integrative flame photometer. The quantity of fiber water was determined by correcting the weight of the fiber for the solid component and the adhering and extracellular water. In normal control Ringer's solution the ratio of fiber water to cell weight is 0.79. The intracellular potassium concentration of a fiber bathed in normal control Ringer was determined as 130±10 mM/kg-H20. With propionate substituted for chloride in the control solution, the final intracellular potassium concentration was 128 ±13 mM/kg-H2O. The muscle fiber was subjected to media made hyperosmotic by the addition of K salts. When the anion was permeant (chloride) the redistribution of the intracellular potassium conformed to a Donnan system. With the impermeant ion propionate, the fiber behaved as an osmometer. When the media were isosmotically changed with the addition of K salts, the fiber potassium did not conform to a Donnan redistribution with chloride, nor as an osmometer with propionate. When the fiber was suddenly exposed to a propionate control solution after equilibration in chloride, the transient time course of intracellular potassium indicated a predominant water movement. This water movement was probably by electroosmosis.

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