Rat-1 fibroblasts stably overexpressing high levels of human insulin receptor were used as a model system to study the effects of hyperglycemia on insulin receptor tyrosine kinase (IRK) activity and protein kinase C (PKC) translocation in parallel in the intact cell. Glucose (10-25 mM) induced a significant reduction of IRK activity (tyrosine phosphorylation of IR-beta-subunit and IR-substrate-1) within 10 min. This effect was paralleled by a rapid translocation of several PKC isoforms (cPKC alpha, nPKC delta, nPKC epsilon, nPKC zeta) to the plasma membrane within 1 min. Kinetics of IRK inhibition and PKC translocation are consistent with the idea that the glucose effect on IRK is mediated by PKC activation. This hypothesis is supported by further observations. Addition of the protein kinase C inhibitor H-7 can prevent the effect of glucose on IRK. Inhibition of IRK is also observed after stimulation of the cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which can substitute for a physiological activator of PKC. Glucose (25 mM) increases the 32P incorporation in serine residues of the beta-subunit of IRK. We conclude that high levels of glucose induce inhibition of IRK in vivo. There is indirect evidence that this effect is mediated by a glucose-induced PKC translocation/activation and serine phosphorylation of the insulin receptor.