Isometric contractile properties and caffeine sensitivity of the diaphragm, EDL and soleus in the mouse.

1. Isometric contractile responses and caffeine sensitivity were studied in isolated mouse hemidiaphragm (HD), extensor digitorum longus (EDL) and soleus muscles. 2. The maximum twitch and tetanic tensions developed by the EDL showed a greater temperature dependence than the soleus. The rates of force development and relaxation were more temperature sensitive in the soleus. 3. For the HD, Q10 values for all contractile parameters were intermediate between those of the EDL and the soleus but closer to those of the EDL. 4. The soleus was significantly more sensitive to caffeine than the EDL while the HD showed a response closer to that of the EDL than the soleus. 5. Costal segments of the HD developed force more rapidly but were less caffeine sensitive than the vertebral or sternal segments. 6. The results indicate that the mouse HD exhibits isometric contractile characteristics and caffeine sensitivity more closely resembling the EDL than the soleus but there is a variation in these properties between the different parts of the HD.