The effect of glibenclamide on frog skeletal muscle: evidence for K+ATP channel activation during fatigue.

Abstract

1. The purpose of this study was to determine whether ATP-sensitive K+ (KATP) channels are activated and contribute to the decrease in force during fatigue development in the sartorius muscle of the frog, Rana pipiens. Tetanic force (elicited by field stimulation), action potential and membrane conductance (using conventional microelectrodes), were measured in the presence and absence of glibenclamide, a KATP channel antagonist. Experiments were performed in bicarbonate-buffered solutions at pH 7-2.2. In unfatigued muscle 100 ,umol I-' glibenclamide had no effect on the resting potential, the overshoot, the half-depolarization time or the maximum rate of depolarization of action potentials, while the mean half-repolarization time increased by 19 ± 4 % (± S.E.M.) and the maximum rate of repolarization decreased by 17 + 5 %. 3. Fatigue was elicited using 100 ms tetanic contractions every I s for 3 min. In the absence of glibenclamide the mean half-repolarization time increased from 057 + 005 to 089 + 0 05 ms during fatigue. The mean half-repolarization times after fatigue, when muscle fibres were exposed to 100 ,umol I1 glibenclamide either 60 min prior to fatigue or 60 s before the end of fatigue, were 1-16 + 0-08 and 1t17 + 0 07 ms respectively.Application of 100 #smol I-' glibenclamide after 5 min of recovery did not increase the half-repolarization time, but decreased the rate of recovery compared to control values.4. In unfatigued muscles, 100 jumol I' glibenclamide did not affect the tetanic contraction. In the absence of glibenclamide, the mean tetanic force after fatigue was 11 0 + 0 9 % of prefatigue values. Application of 100 umol I' glibenclamide 60 min before fatigue increased the rate of fatigue development as the mean tetanic force was 4-8 + 0-8 % after 3 min of stimulation. The addition of 100 ,umol I-' glibenclamide 60 s before the end of fatigue had no effect on tetanic force during this time compared to control. 5. In the absence of glibenclamide, muscles recovered 90-1 + 1-6 % of their tetanic force after 100 min. Addition of 100,umol I' glibenclamide 60 min prior to fatigue significantly reduced the capacity of muscles to recover their tetanic force: after 100 min of recovery tetanic force was only 47-3 + 9.4 % of the pre-fatigue value. Application of 100 jumol I' glibenclamide 60 s prior to the end of fatigue had a much smaller effect on the recovery as 79.4 + 6'2 % of the tetanic force was recovered in 100 min. Addition of glibenclamide after 5 min of recovery had no effect. 6. The results from this study support the proposal that KATP channels are activated during fatigue and they contribute to the repolarization phase of the action potential. Although no evidence was found that activation of KATP channels during fatigue contributes to the force decrease during fatigue development, the impairment of force recovery following fatigue in the presence of glibenclamide supports the notion that KATP channels play an important protective role.

Distinct Histidine Residues Control the Acid-induced Activation and Inhibition of the Cloned KATP Channel

“…ϩ (K ATP ) channels couple the intermediary metabolism to cellular activity and play important roles in numerous cellular functions such as insulin secretion, neuronal excitability, vascular tones, and muscle contractability (1)(2)(3)(4)(5)(6). The K ATP channels consist of the pore-forming Kir6 and sulfonylurea receptor (SUR) 1 subunits.…”

Skeletal muscle fatigue – regulation of excitation–contraction coupling to avoid metabolic catastrophe

“…In the absence of K ATP channel activity, the depolarization can be as high as 50 mV under both conditions. This depolarization has been shown to be sufficiently large enough to activate the Ca 2+ channels in transverse tubules, leading to an uncontrolled Ca 2+ influx, large increases in resting intracellular Ca 2+ and in force (Cifelli et al, 2008;Cifelli et al, 2007;Gong et al, 2000;Light et al, 1994;Matar et al, 2000). As a consequence of the increases in resting [Ca 2+ ], there is greater use of ATP by the Ca 2+ and myosin ATPases, which worsen the possibility of a metabolic catastrophe.…”

“…at between 10 and 15 mV during repeated muscle contractions (Cifelli et al, 2008;Comtois et al, 1995;Light et al, 1994), whereas it does not change during metabolic inhibition (Gramolini and Renaud, 1997). In the absence of K ATP channel activity, the depolarization can be as high as 50 mV under both conditions.…”

Localization and function of ATP-sensitive potassium channels in human skeletal muscle

“…It was demonstrated that ATP inhibits the K ATP channels and that the inhibitory effect of ATP is reduced by lowering of pH (6). It was originally suggested that the channels are activated only in metabolically exhausted muscle fibers (4) and that the activity of the channels contributes to the decrease in force during fatigue in frog muscle (15). However, this hypothesis is not supported by later studies also using frog muscle (20).…”