Fructose 2,6-bisphosphate in rat skeletal muscle during contraction

Abstract

Fructose 2,6-bisphosphate and several glycolytic intermediates were measured in 2 rat muscles, extensor digitorum longus and gastrocnemius, which were electrically stimulated in situ. Both the duration and the frequency of stimulation were varied to obtain different rates of glycolysis. There was no relationship between fructose 2,6-bisphosphate content and the increase in tissue lactate in contracting muscle. However, in gastrocnemius stimulated at low frequencies (.ltoreq. 5 Hz), there was a 2-fold increase in fructose 2,6-bisphosphate at 10 s, followed by a return to basal values, whereas lactate increased only after 1 min of contraction. The concentrations of hexose 6-phosphates, fructose 1,6-bisphosphate and triose phosphates were all increased during the 3 min stimulation. During tetanus (frequencies .gtoreq. 10 Hz) fructose 2,6-bisphosphate was not increased, whereas glycolysis was maximally stimulated and resulted in an accumulation of tissue lactate, mostly from glycogen. The concentrations of hexose 6-phosphate increased continuously during the 1 min tetanus, whereas fructose, 1,6-bisphosphate was increased at 10 s and then decreased progressively. It therefore appears that fructose 2,6-bisphosphate does not play a role in the stimulation of glycolysis during tetanus; it may however, be involved in the control of glycolysis when the muscles are stimulated at low frequencies for short periods of time.