Changes in glucose transport and protein kinase C beta(2) in rat skeletal muscle induced by hyperglycaemia

Aims/hypothesis. We have previously reported that hyperglycaemia activates glucose transport in skeletal muscle by a Ca2+-dependent pathway, which is distinct from the insulin-signalling pathway. The aim of this study was to explain the signalling mechanism by which hyperglycaemia autoregulates gluc ose transport in skeletal muscle. Methods. Isolated rat soleus muscle was incubated in the presence of variou s concentrations of glucose or 3-O-methylglucose and protein kinase C and p hospholipase C inhibitors. Glucose transport activity, cell surface glucose transporter 1 and glucose transporter 4 content and protein kinase C trans location was determined. Results. High concentrations of 3-O-methylglucose led to a concentration-de pendent increase in [H-3]-3-O-methylglucose transport in soleus muscle. Dan trolene, an inhibitor of Ca2+ released from the sarcoplasmic reticulum, dec reased the V-max and the K-m of the concentration-response curve. Protein k inase C inhibitors (H-7 and GF109203X) inhibited the stimulatory effect of high glucose concentrations on hexose transport, whereas glucose transport stimulated by insulin was unchanged. Incubation of muscle with glucose (25 mmol/l) and 3-O-methylglucose (25 mmol/l) led to a three fold gain in prote in kinase C beta(2) in the total membrane fraction, whereas membrane conten t of protein kinase C alpha, beta(1), delta, epsilon and theta were unchang ed. A short-term increase in the extracellular glucose concentration did no t change cell surface recruitment of glucose transporter 1 or glucose trans porter 4, as assessed by exofacial photolabelling with [H-3]-ATB-BMPA bis-m annose. Conclusion/interpretation. Protein kinase C beta(2) is involved in a glucos e-sensitive, Ca2+-dependent signalling pathway, which is possibly involved in the regulation of glucose transport in skeletal muscle. This glucose-dep endent increase in 3-O-methylglucose transport is independent of glucose tr ansporter 4 and glucose transporter 1 translocation to the plasma membrane and may involve modifications of cell surface glucose transporter activity.