Influence of tension time on muscle fiber sarcolemmal injury in rat diaphragm.
We hypothesized that the amount of sarcolemmal injury is directly related to the total tension time (TT(tot)), calculated as mean tension x total stimulation time. Diaphragm strips from Sprague-Dawley rats were superfused at optimal muscle length with Krebs containing procion orange to identify sarcolemmal injury. TT(tot) was induced by stimulation with 100 Hz for 3 min at duty cycles of 0.02, 0.15, 0.3, and 0.6, or with continuous contractions at 0.2, 0.4, 0.6, and 1.0 of maximal tension. A significant positive correlation between TT(tot) and the percentage of fibers with injured sarcolemma (r(2) = 0.63, P < 0.05) is seen. Stimulation (at 100 Hz, duty cycle = 1) resulted in fast fatigue with low injury, likely caused by altered membrane conductivity. Stimulations inducing the largest injury are those showing progressive force loss and high TT(tot), where injury may be due to activation of membrane degradative enzymes. The maximal tension measured at 20 min poststimulation was inversely related to the number of fibers injured, suggesting loss of force is caused by cellular injury.
Zhu
E
E
Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada H2L 4M1.
Comtois
A S
AS
Fang
L
L
Comtois
N R
NR
Grassino
A E
AE
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D003964:Diaphragm / Q000473:pathology* / Q000502:physiology; D004553:Electric Conductivity; D004558:Electric Stimulation; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000473:pathology* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000473:pathology*; D013997:Time Factors; D014227:Triazines
D014227:Triazines; C009045:procion brilliant orange M-2RS