The sarcoplasmic calcium levels of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscle of the rat were measured during caffeine superfusion, to test the hypothesis that the different sensitivity of the two muscle types for this substance is due to different characteristics of the calcium metabolism of the two fiber types. To this end [Ca2+]i was determined in these fiber types. Understanding of [Ca2+]i signal in skeletal muscle is hampered by the lack of [Ca2+]i quantification in the fibers in situ. In the present study, the Indo-1 ratiometric method, using intravital microscopy with DCCD camera for collecting fluorescence images, was adapted to measure [Ca2+]i in vivo. To demonstrate the usefulness of the model we report the first determinations of caffeine induced [Ca2+]i transients in muscle fibers (SOL and EDL). Caffeine - superfused for 2 min. at 37°C: 1, 2, 5, 10 mmol/1 - induced an increase in [Ca2+]i increase in a dose-dependent manner (SOL: 0%, 13.5%, 18.3%, 44.0%; EDL: 0%, 0%, 4.8%, 14.8%, respectively), revealing differences between fibers in threshold concentration and peak responses. These results thus support the hypothesis, that slow-twitch fibers are more sensitive to caffeine than fast-twitch fibers. The different kinetics of the release channels in the two fiber types and the slowed reuptake by the SR may explain the apparent differences in [Ca2+], changes evoked by caffeine.
|Publication status||Published - Mar 20 1998|
ASJC Scopus subject areas
- Molecular Biology