Type IV collagen, which is encoded by six genetically distinct alpha-chains (alpha1-alpha6), is a major component of the kidney glomerulus. The alpha1(IV) and alpha2(IV) chains are present predominantly in the mesangial matrix, whereas the alpha3(IV), alpha4(IV), and alpha5(IV) chains are localized almost exclusively to the glomerular basement membrane (GBM). Thickening of the GBM and expansion of the mesangial matrix are believed to contribute to the pathogenesis of diabetic nephropathy. In the present study, we evaluated the expression of alpha1(IV), alpha3(W), and alpha5(IV) chains in rat glomerular endothelial (GEndC) and mesangial cells (GMC). Under physiological concentrations of glucose (5 mM), alpha1(IV) and alpha5(IV) chains were detectable in GMCs, with an obvious absence of alpha3(IV) chain. All three isoforms tested were present in GEndCs. At diabetic concentrations of glucose (25 mM), alpha1(IV) was up-regulated in GMCs, whereas expression level of alpha1(IV) remained unaltered in GEndCs. The alpha3(IV) and alpha5(IV) chains were up-regulated in GEndCs, but remained unchanged in GMCs under diabetic glucose concentrations (25 mM). Collectively, our results demonstrate that GMC might contribute to mesangial matrix expansion, mediated by alpha1(IV) collagen, while GEndC might contribute to thickening of GBM, mediated by alpha3(IV) collagen, in patients with diabetic nephropathy. (C) 2002 Elsevier Science (USA). All rights reserved.