Changes in glucose transport and protein kinase Cβ2 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 glucose transport in skeletal muscle. Methods. Isolated rat soleus muscle was incubated in the presence of various concentrations of glucose or 3-O-methylglucose and protein kinase C and phospholipase C inhibitors. Glucose transport activity, cell surface glucose transporter 1 and glucose transporter 4 content and protein kinase C translocation was determined. Results. High concentrations of 3-O-methylglucose led to a concentration-dependent increase in [H-3]-3-O-methylglucose transport in soleus muscle. Dantrolene, an inhibitor of Ca2+ released from the sarcoplasmic reticulum, decreased the V-max and the K-m of the concentration-response curve. Protein kinase 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 protein kinase C beta(2) in the total membrane fraction, whereas membrane content of protein kinase C alpha, beta(1), delta, epsilon and theta were unchanged. A short-term increase in the extracellular glucose concentration did not change cell surface recruitment of glucose transporter 1 or glucose transporter 4, as assessed by exofacial photolabelling with [H-3]-ATB-BMPA bis-mannose. Conclusion/interpretation. Protein kinase C beta(2) is involved in a glucose-sensitive, Ca2+-dependent signalling pathway, which is possibly involved in the regulation of glucose transport in skeletal muscle. This glucose-dependent increase in 3-O-methylglucose transport is independent of glucose transporter 4 and glucose transporter 1 translocation to the plasma membrane and may involve modifications of cell surface glucose transporter activity.