Selective Long‐Term Electrical Stimulation of Fast Glycolytic Fibres Increases Capillary Supply but not Oxidative Enzyme Activity in Rat Skeletal Muscles

Abstract

Glycolytic fibres in rat extensor digitorum longus (EDL) and tibialis anterior (TA) were selectively activated, as demonstrated by glycogen depletion, by indirect electrical stimulation via electrodes implanted in the vicinity of the peroneal nerve using high frequency (40 Hz) trains (250 ms at 1 Hz) and low voltage (threshold of palpable contractions). This regime was applied 10 times per day, each bout being of 15 min duration with 60 min recovery, for 2 weeks. Cryostat sections of muscles were stained for alkaline phosphatase to depict capillaries, succinate dehydrogenase (SDH) to demonstrate oxidative fibres, and periodic acid‐Schiff reagent (PAS) to verify glycogen depletion. Specific activity of hexokinase (HK), 6‐phosphofructokinase, pyruvate kinase, glycogen phosphorylase and cytochrome c oxidase (COX) were estimated separately in homogenates of the EDL and the predominantly glycolytic cortex and oxidative core of the TA. Stimulation increased the activity of HK but not that of oxidative enzymes in fast muscles. Comparison of changes in oxidative capacity and capillary supply showed a dissociation in the predominantly glycolytic TA cortex. Here, COX was 3.9 ± 0.68 μM min‐1 (g wet wt)‐1 in stimulated muscles compared with 3.7 ± 0.52 μM min‐1 (g wet wt)‐1 in contralateral muscles (difference not significant), while the percentage of oxidative fibres (those positively stained for SDH) was also similar in stimulated (14.0 ± 2.8%) and contralateral (12.2 ± 1.9%) muscles. In contrast, the capillary to fibre ratio was significantly increased (2.01 ± 0.12 vs. 1.55 ± 0.04, P < 0.01). We conclude that capillary supply can be increased independently of oxidative capacity, possibly due to haemodynamic factors, and serves metabolite removal to a greater extent than substrate delivery.

Electrical Stimulation of Denervated Rat Skeletal Muscle Retards Capillary and Muscle Loss in Early Stages of Disuse Atrophy

“…In general, relatively higher intensities or frequencies of ES are likely to result in greater effects on muscle atrophy and capillary regression in early-stage DN-induced disuse. Muscle stimulation with higher-frequency ES regimens (20–100 Hz) tends to show beneficial effects of reducing the disuse-induced decreases in muscle mass, FCSA, and capillary supply [15, 25, 40–42]. However, a low-frequency ES regimen (10 Hz, 8 and 16 mA, 30 min/day, for 3 weeks) in stimulated TA muscle retarded the atrophy of denervated muscle [13].…”

The α-subunit of AMPK is essential for submaximal contraction-mediated glucose transport in skeletal muscle in vitro

“…Of more concern is that Fujii and colleagues opted to use a nonsupramaximal voltage (8.4 -21 V) in the WT group to match force production to the level of the ␣ 2 i TG animals that were stimulated with a supramaximal voltage (i.e., Ͼ30 V). However, during electrical stimulation of isolated muscles ex vivo and particularly in the context of measuring glucose uptake, it is imperative that the voltage remains supramaximal to ensure activation of all (especially the deepest) muscle fibers (9). Thus the option of reducing the stimulation voltage in the WT mice would inevitably lead to a lesser recruitment of the deepest muscle fibers, even though the work load was equal to that of ␣ 2 i TG muscle.…”

Cardiovascular Adaptations to Exercise Training

“…However, in interval sprint exercise, with energy supply originating mainly from anaerobic energy production, an increased capillarization may allow for faster oxygen dependent metabolic recovery processes and serve to improve the removal of metabolic waste products such as lactate. The latter physiological function is supported by a study showing that selective chronic electrical stimulation of glycolytic fast twitch fibers led to an increase in capillarization (98).…”