Vascular endothelial growth factor (VEGF-A) exerts its effects through receptor tyrosine kinases VEGF receptor-1 (VEGFR-1) and VEGFR-2, which are expressed on most endothelial cell types in vitro and in vivo. We have examined VEGF-A-induced signal transduction in porcine aortic endothelial (PAE) cells individually expressing VEGFR-1 or VEGFR-2, and cells co-expressing both receptor types. We show that VEGF-A-stimulated PAE cells co-expressing VEGFR-1 and -2 contain receptor heterodimers. VEGF-A-stimulation of all three cell lines (expressing VEGFR-1, -2 and -1/2) resulted in signal transduction with different efficiencies. Thus, tyrosine phosphorylation of phospholipase Cgamma, and accumulation of inositol polyphosphates were efficiently transduced in the VEGFR-1/2 cells whereas cells expressing VEGFR-1 responded poorly in these assays. In contrast, VEGF-A-induced activation of phosphoinositide 3-kinase and induction of Ca2+ fluxes were transduced well by VEGFR-1 and VEGFR-2 homo- and heterodimers. The pattern of Ca2+ fluxes was unique for each type of VEGF receptor dimer. Our data show that signal transduction induced by VEGF-A is transduced in distinct manners by homo- and heterodimers of VEGF receptors.