In vitro glucose uptake induced by electrical stimulation in soleus muscle. Does the stimulation frequency matter?

Objectives: Glucose uptake of skeletal muscle has been studied widely in vitro using electrical stimulation. High frequency stimulation resulted in higher glucose uptake. Since the physiological stimulation pattern for slow-twitch muscles is at low frequencies, this study aims to analyse the effects of low vs. high frequency stimulation on glucose uptake in vitro and on muscle structure in the slow-twitch rat soleus muscle. Design: Eighteen Wistar rats were assigned to two groups: stimulation at 10Hz and at 100Hz of isolated soleus muscles in an oxygenated Krebs buffer. Glucose uptake and the intrafiber localization of GLUT4 were determined. As an estimate for potential damage, the release of taurine into the buffer, cleaved caspase-3 occurrence and expression, and morphological signs of fiber damage were quantified. Results: Stimulation at 100Hz resulted in a more pronounced glucose uptake than at 10Hz. However, the muscles stimulated at 100Hz showed signs of cellular and membrane damage more frequently than the 10Hz-muscles. Therefore, cellular damage might account for an artificial glucose influx from the buffer by muscles stimulated at 100Hz. Conclusion: It does not seem meaningful to study glucose uptake in slow-twitch muscles with non-physiologically high stimulation frequencies.