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Charge movement and mechanical repriming in skeletal muscle.
Author(s) -
Adrian R H,
Chandler W K,
Rakowski R F
Publication year - 1976
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1976.sp011236
Subject(s) - biophysics , contraction (grammar) , depolarization , membrane potential , chemistry , refractory period , materials science , anesthesia , medicine , biology
1. Muscles were placed in a solution which depolarized the membrane to ‐30 to ‐20 mV so that mechanical activation was made refractory. Mechanical repriming and the recovery of voltage dependent charge movement were studied using a voltage clamp technique. 2. Mechanical repriming was investigated by determining the duration of a hyperpolarizing pulse required to elicit a just‐visible contraction for various post‐pulse potentials. As the post‐pulse potential was made more positive shorter repriming times were required to produce a threshold contraction. The relationship approached a minimum repriming time for very positive post‐pulse potentials. 3. These results suggest that hyperpolarization gradually removes some component of the activation mechanism from a refractory state and that the effectiveness of the amount which has recovered depends on the post‐pulse potential. A quantitative explanation is given using a simple model in which the essential component is assumed to be the charge movement process. 4. The rate of repriming contraction is voltage dependent; at ‐160 mV the rate is about twice that at ‐120 mV. Between 4 and 10 degrees C the rate has a Q10 of about 9. 5. Recovery of charge movement was studied using a repriming duration less than that required to produce a threshold contraction. The observed charge movement increased linearly with repriming time, consistent with the approximately linear initial segment of a slow exponential recovery process. Extrapolation of the recovery curve indicated that 2‐5 n/CmuF of charge is reprimed in the time necessary to reprime a threshold contraction. 6. The charge which recovers during a subthreshold repriming pulse is distributed according to membrane potential in the same way as a fully reprimed charge. 7. These results are consistent with the hypothesis that voltage dependent charge movement is an intermediate step in excitation‐contraction coupling. 8. The characteristics of a second type of charge movement are also described.