Increased depolarization, prolonged recovery and reduced adaptation of the resting membrane potential in aged rat skeletal muscles following eccentric contractions.
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.
McBride
T
T
Department of Biology, California State University, Bakersfield, CA 93311, USA. tmcbride@csubak.edu
D000222:Adaptation, Physiological; D000375:Aging / Q000502:physiology*; D000818:Animals; D005260:Female; D005682:Gadolinium / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013307:Streptomycin / Q000494:pharmacology
D007473:Ion Channels; D005682:Gadolinium; D013307:Streptomycin