Increased depolarization, prolonged recovery and reduced adaptation of the resting membrane potential in aged rat skeletal muscles following eccentric contractions.

摘要

Previously it was shown in young-adult muscles that eccentric contractions (EC) produce a significant (24 h) depolarization of the resting membrane potential (RMP), and that in-vitro (Gd(3+)) and in-vivo (streptomycin) blockade of stretch activated ion channels (SAC) result in a partial repolarization of the RMP. The portion of the depolarization not restored by SAC blockade is believed to be from sarcolemmal injury. A second exposure to EC results in less depolarization and a more rapid recovery of the RMP. Aged muscles were subjected to the same EC protocol to test the hypotheses that: (1) Aged muscles will experience a more significant and prolonged depolarization of the RMP following EC. (2) The depolarization in aged muscles will occur by a greater contribution from membrane damage, rather than the opening of SAC. (3) The aged muscles will demonstrate a reduced capacity to adapt to EC, and will experience a similar degree of depolarization following repeated exposures to EC. The results indicate a significantly greater and longer lasting depolarization in aged compared to young-adult muscles. Blocking SAC did not produce a repolarization of the RMP in aged muscles. Aged muscles had a significantly reduced adaptive response to EC compared to young-adult. It is speculated that the different response in aged muscles results from a reduced number of functional SAC.