Effect of force development on contraction induced glucose transport in fast twitch rat muscle

A previous study has shown that in fast twitch frog sartorius muscle contra ction stimulated glucose transport depends only on stimulation frequency an d not on workload. In contrast, we have recently shown that in rat slow twi tch muscle stimulated to contract at constant frequency, glucose transport varies directly with force development and, in turn, metabolism. The presen t study was carried out to clarify whether the discrepancy between the earl ier studies reflected differences in physiological behaviour between fast a nd slow twitch muscle. We investigated the effect of force development on g lucose transport in incubated fast twitch rat flexor digitorum brevis (rich in type 2a fibres) and epitrochlearis (rich in type 2b fibres) muscle. Mus cles were electrically stimulated to perform repeated tetanic contractions at 1 Hz for 10 min. Resting length was adjusted to achieve either no force or maximum force. Glucose transport (2-deoxyglucose uptake) increased when force was produced compared with when it was not (P < 0.05) in both flexor digitorum brevis (19 +/- 7 (basal). 163 +/- 14 (no force) and 242 +/- 17 (m ax force) nmol x g(-1) x 5 min(-1)) and epitrochlearis (60 +/- 4 (basal). 1 00 +/- 7 (no force) and 125 +/- 6 (max force) nmol x g(-1) x 5 min(-1)). In both muscles glucose transport increased in parallel with metabolic rate, as reflected by muscle lactate concentrations and 5' AMP-activated protein kinase activity, during contractions. In conclusion. as previously shown fo r rat soleus muscle, at a given stimulation frequency glucose transport var ies directly with force development in rat flexor digitorum brevis and epit rochlearis muscle. Accordingly, force development enhances glucose transpor t in all mammalian muscle fibre types. The influence of force development p robably reflects effects of enhanced 5' AMP-activated protein kinase activi ty resulting from reduced intra-cellular energy status and pH.