The cellular mechanism for the effects of glyburide on the synthesis and release of insulin and insulin gene expression in isolated islets was investigated. On incubation for 1 h, glyburide increased insulin release without affecting either the insulin content or the PPI mRNA level. H-7, an inhibitor of PKC, inhibited the glyburide-induced insulin release, while H-8, an inhibitor of cyclic nucleotide-dependent protein kinases, did not affect the glyburide-induced insulin release. On incubation for 20 h, glyburide increased insulin release and the PPI mRNA level, without affecting the insulin content. H-7 inhibited glyburide-induced insulin release and increased the PPI mRNA level. H-8 significantly inhibited both the glyburide-induced increase in insulin release and increase in PPI mRNA level. In conclusion, glyburide stimulated insulin release via a PKC-mediated pathway and increased the PPI mRNA level via cyclic nucleotide-dependent protein kinase(s).