Membrane leakage and increased content of Na super(+) K super(+) pumps and Ca super(2+) in human muscle after a 100-km run

During prolonged exercise, changes in the ionic milieu in and surrounding the muscle fibers may lead to fatigue or damage of the muscle and thereby impair performance. In 10 male subjects, we investigated the effects of 100 km running on muscle and plasma electrolyte contents, muscle Na super(+)-K super(+) pump content, and plasma concentrations of creatine kinase (CK) and lactate dehydrogenase (LDH). After completion of a 100-km run, significant increases were found in plasma K super(+) (from 4.0 plus or minus 0.1 to 5.5 plus or minus 0.2 mM, P < 0.001), muscle Na super(+)-K super(+) pump content (from 334 plus or minus 11 to 378 plus or minus 17 pmol/g, P < 0.05), and total muscle Ca super(2+) content (from 0.84 plus or minus 0.03 to 1.02 plus or minus 0.04 mu mol/g, P < 0.001). There was also a large increase in the plasma levels of the muscle-specific enzymes CK and LDH, which reached peak values at the end of the run and lasted several days after the run, indicating that a significant degree of muscle membrane leakage was present. The simultaneous occurrence of raised cellular Ca super(2+) content and muscle membrane leakage supports the theory that Ca super(2+) plays a role in the initiation of degenerative processes in muscles after severe exercise.