Glibenclamide increases post-fatigue tension in slow skeletal muscle fibers of the chicken
In contrast to fast-twitch skeletal muscle fibers of the chicken, slow-twitch fibers are fatigue-resistant. In fast fibers, the fatigue process has been related to KATP channels. In the present study, we investigated the action of glibenclamide (an anti-diabetic sulphonylurea that acts on KATP channels) on fatigued slow skeletal muscle, studying twitch and tetanus tension after inducing the muscle to fatigue by continuous electrical stimulation. Our results showed that glibenclamide (150 μM) increased post-fatigue twitch tension by about 25% with respect to the fatigued condition (P < 0.05). In addition, glibenclamide (150 μM) increased post-fatigue tetanic tension (83.61 ± 15.7% in peak tension, and 85.0 ± 19.0% in tension-time integral, P = 0.02, and 0.04, respectively; n = 3). Moreover, after exposing the muscle to a condition that inhibits mitochondrial ATP formation in order to activate KATP channels with cyanide (10 mM), tension also diminished, but in the presence of glibenclamide the effect produced by cyanide was abolished. To determine a possible increase in intracellular calcium concentration, the effects of glibenclamide on caffeine-evoked contractures were explored. After muscle pre-incubation with glibenclamide (150 μM), tension of caffeine-evoked contractures increased (6.5 ± 1.5% in maximal tension, and 5.9 ± 3.8% in tension-time integral, P < 0.05). These results suggest a possible role of KATP channels in the fatigue process, since glibenclamide increases twitch and tetanus tension in fatigued slow muscle of the chicken and during metabolic inhibition, possibly by increasing intracellular calcium.