TY - JOUR
T1 - Correlated reduction of velocity of shortening and the rate of energy utilization in mouse fast-twitch muscle during a continuous tetanus
AU - Crow, Michael T.
AU - Kushmerick, Martin J.
PY - 1983/11/1
Y1 - 1983/11/1
N2 - Isometric tetani of slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of the mouse were studied at 20°C. The total energy cost for 3- and 9-s isometric tetani was measured as a function of length above Lo and partitioned into a filament overlap-dependent fraction and a smaller filament overlap-independent fraction. In both muscles, the rate of filament overlap-independent energy cost did not change with tetanic duration. In the EDL, but not in the soleus, the rate of filament overlap-dependent energy utilization was greater in a 3-s tetanus than in a 9-s tetanus. The forcevelocity relationships were studied after 3 and 9 s of isometric tetanus. In the soleus, Vmax was 2 fiber lengths/s and was not dependent on the duration of isometric tetanus. In contrast, in the EDL, Vmax decreased from 5.9 fiber lengths/s at 3 s to 3.9 fiber lengths/s at 9 s. The velocity of unloaded shortening (Vus) was examined by the slack test method as a function of the duration of isometric tetanus duration over the range of 1-15s. In the soleus, Vus did not change, whereas in the EDL, Vus declined progressively from 6.4 to 3.2 fiber lengths/s after an isometric tetanus of increasing duration from 1 to 15s. These results cannot exclude the hypothesis that in a maintained tetanus there is a decrease in the intrinsic cross-bridge turnover rate in the fast-twitch EDL, but not in the slow-twitch soleus muscle.
AB - Isometric tetani of slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of the mouse were studied at 20°C. The total energy cost for 3- and 9-s isometric tetani was measured as a function of length above Lo and partitioned into a filament overlap-dependent fraction and a smaller filament overlap-independent fraction. In both muscles, the rate of filament overlap-independent energy cost did not change with tetanic duration. In the EDL, but not in the soleus, the rate of filament overlap-dependent energy utilization was greater in a 3-s tetanus than in a 9-s tetanus. The forcevelocity relationships were studied after 3 and 9 s of isometric tetanus. In the soleus, Vmax was 2 fiber lengths/s and was not dependent on the duration of isometric tetanus. In contrast, in the EDL, Vmax decreased from 5.9 fiber lengths/s at 3 s to 3.9 fiber lengths/s at 9 s. The velocity of unloaded shortening (Vus) was examined by the slack test method as a function of the duration of isometric tetanus duration over the range of 1-15s. In the soleus, Vus did not change, whereas in the EDL, Vus declined progressively from 6.4 to 3.2 fiber lengths/s after an isometric tetanus of increasing duration from 1 to 15s. These results cannot exclude the hypothesis that in a maintained tetanus there is a decrease in the intrinsic cross-bridge turnover rate in the fast-twitch EDL, but not in the slow-twitch soleus muscle.
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U2 - 10.1085/jgp.82.5.703
DO - 10.1085/jgp.82.5.703
M3 - Article
C2 - 6644272
AN - SCOPUS:0020972752
SN - 0022-1295
VL - 82
SP - 703
EP - 720
JO - Journal of General Physiology
JF - Journal of General Physiology
IS - 5
ER -