Skeletal muscle the KATP channel is important in protecting energy levels and abolishing its activity causes fiber damage and severely impairs function. The responses to a lack of KATP channel activity vary between muscles and fibers, with the severity of the impairment being the highest in the most glycolytic muscle fibers. Furthermore, glycolytic muscle fibers are also expected to face metabolic stress more often than oxidative ones. The objective of this study was to determine whether the t-tubular KATP channel content differ between muscles and fiber types. KATP channel content was estimated using a semi-quantitative immunofluorescence approach by staining cross-sections from soleus, extensor digitorum longus (EDL) and flexor digitorum brevis (FDB) muscles with anti-Kir6.2 antibody. Fiber types were determined using serial cross-sections stained with specific anti-myosin I, IIA, IIB and IIX antibodies. Changes in Kir6.2 content were compared to changes in CaV1.1 content, as this Ca2+ channel is responsible for triggering Ca2+ release from sarcoplasmic reticulum. The Kir6.2 content was the lowest in the oxidative soleus and the highest in the glycolytic EDL and FDB. At the individual fiber level, the Kir6.2 content within a muscle was in the order of type IIB > IIX > IIA ≥ I. Interestingly, the Kir6.2 content for a given fiber type was significantly different between soleus, EDL and FDB, being the highest in FDB. Correlations of relative fluorescence intensities from the Kir6.2 and CaV1.1 antibodies were significant for all three muscles. However, the variability in content between the three muscles or individual fibers was much greater for Kir6.2 than for CaV1.1. It is suggested that the t-tubular KATP channel content increases as the glycolytic capacity increases and as the oxidative capacity decreases and that the expression of KATP channels may be linked to how often muscles/fibers face metabolic stress.
- Muscle fatigue
- KATP channels
- Skeletal muscle
- fiber type
- Copyright © 2010, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology