Glucose uptake and metabolic stress in rat muscles stimulated electrically with different protocols

In the present study, the relationship between the pattern of electrical stimulation and glucose uptake was investigated in slow-twitch muscles (soleus) and fast-twitch muscles (epitrochlearis) from Wistar rats. Muscles were stimulated electrically for 30 min in vitro with either single pulses (frequencies varied between 0.8 and 15 Hz) or with 200-ms trains (0.1-2 Hz). Glucose uptake (measured with tracer amount of 2-[³H] deoxyglucose) increased with increasing number of impulses whether delivered as single pulses or as short trains. The highest glucose uptake achieved with short tetanic contractions was similar in soleus and epitrochlearis (10.9 ± 0.7 and 12.0 ± 0.8 mmol·kg dry wt^-1·30 min^-1, respectively). Single pulses, on the other hand, increased contraction-stimulated glucose uptake less in soleus than in epitrochlearis (7.5 ± 1.1 and 11.7 ± 0.5 mmol·kg dry wt^-1·30 min^-1, respectively; P < 0.02). Glucose uptake correlated with glycogen breakdown in soleus (r = 0.84, P < 0.0001) and (epitrochlearis: r = 0.91, P < 0.0001). Contraction-stimulated glucose uptake also correlated with breakdown of ATP and PCr and with reduction in force. Our data suggest that metabolic stress mediates contraction-stimulated glucose uptake.