Insulin signaling to generate inositol phosphoglycans (IPGs) was demonstrated to occur via the participation of the heterotrimeric G-proteins G(q/11). IPGs were measured as two specific inositol markers, myo-mositol and chiro-inositol after strong acid hydrolysis. Insulin and Pasteurella multocida toxin (PMT) generated both myo-mositol and chiro-inositol IPGs in a dose-dependent manner. PMT has been shown to activate G(q) specifically. Insulin action was abrogated by pre-treatment with anti G(q/11) antibody. Western blotting demonstrated the enrichment of both insulin receptor beta subunit and Gq/11 in the liver membrane vesicles. Vesicles also contained clathrin, caveolin PLC beta1 and PLCDelta. Immunogold staining revealed the co-localization of both insulin receptor beta subunit and Gq/11 in an approximate stochiometric ratio of 1:3. No vesicles were detected with either component alone. The present and considerable published data provide strong evidence for insulin signaling both via a tyrosine kinase cascade mechanism and via heterotrimeric G-protein interactions. (C) 2002 Elsevier Science (USA). All rights reserved.