On the Mechanism of Lactate Dehydrogenase Release from Skeletal Muscle in Relation to the Control of Cell Volume

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Abstract
The mechanism of enzyme release from isolated rat skeletal muscle was illustrated by the study of the release of lactate dehydrogenase (LDH). In hypotonic media of different composition but of same tonicity, the increase of LDH permeability was triggered at the same range of relative osmolality R (0.45 < R < 0.55), although the swelling in the respective media showed appreciable differences. Muscle swelling kinetics showed that a deviation from the theoretically computed swelling curve to lower values of swelling was connected with an increased LDH permeability. Swelling reduction was ATP- and Ca2+ and/or Mg2-dependent. Swelling of cells generally precedes the leakage of soluble enzymes, and the cross-linking of filaments at the sarcoplasmic side of the sarcolemma under appropriate conditions can counteract swelling, thereby blebbing off the cell membrane from the filament meshwork. In the course of this process, sufficiently large membrane lesions are produced through which macromolecules may escape into the extracellular space.

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