Extracellular nucleotides increase albumin permeability of isolated intact wistar rat glomeruli.

INTRODUCTION: Renal glomeruli consist of endothelial cells, mesangial cells, acellular basement membrane and epithelial cells called podocytes. Interactions between these cells and amorphic membrane affect the glomerular barrier function. Activity of these cells is regulated by extracellular nucleotides via P2-receptors in para-/autocrine manner. These receptors are nucleotides-gated ion-channels receptors (P2X) and G protein-coupled receptors (P2Y). The expression of purinoceptors is up-regulated in some forms of chronic renal injury and inflammatory diseases characterized by increased glomerular permeability leading to development of albuminuria/proteinuria, a sign of kidney disease and independent risk factor for the progression of renal failure and for cardiovascular morbidity and mortality. AIM: The aim of study was to investigate the effects of P2-receptors activation on glomerular-capillary permeability for albumin. METHODS: The osmotic pumps (ALZET, model 2001, reservoir volume 200µl, pumping rate 1µl/hr) with specific and non-selective agonists of P2-receptors, 2-MeSATP (10-6M), ATP-γ-S (10-6M) or buffer were implanted subcutaneously into Wistar rats for 7 days. Afterwards pumps were removed and glomeruli were isolated by sieving technique. Isolated, affixed to a dishes coated with poly-L-lysine, glomeruli were incubated with buffer or natural nucleotides (ATP, ADP, AMP, UTP, UDP) or synthetic nucleotides (2-methylothioATP, ATP-γ-S). Glomerular-capillary permeability for albumin (Palb) was measured as a volume response of glomerular capillaries to an oncopressive medium generated by defined concentrations of albumin. Measurements were conducted using video-microscopy (Olympus IX51). Glomerular volume was derived from the area of glomerular image calculated using CellSens Dimension Software (Olympus). The reflection coefficient of albumin (Salb) was calculated as Salb = ΔVexperimental/ΔVcontrol. Palb was calculated as Palb = 1-Salb. Cultured rat podocytes were used for immunofluorescence studies. RESULTS: Palb in control glomeruli was 0.10±0.03. 2-MeSATP and ATP-γ-S(10-6M, 10 min, 37°C) induced increase in Palb to 0.58±0.04 and 0.37±0.08, respectively. Palb in glomeruli isolated from rats in vivo exposed to 2-MeSATP or ATP-γ-S (released from osmotic pumps) were significantly increased (0.35±0.03 vs. 0.13±0.02. and 0.52±0.02 vs. 0.13±0.02, respectively). Palb in glomeruli incubated with natural agonists of P2-receptors were increased and amounted to 0.24±0.04 (ATP 10-6M, 2min), 0.34±0.04 (ADP 10-6M, 2min), 0.33±0.05 (AMP 10-6M, 2min), 0.35±0.10(UTP 10-6M, 2min),0.23±0.05(UDP 10-6M, 2min), respectively. 2-MeSATP and ATP-γ-S affects cortical actin remodeling in cultured podocytes. CONCLUSIONS: Our results suggest that activation of P2-receptors increases glomerular-capillary permeability for albumin and may be involved in pathogenesis of renal diseases. [ABSTRACT FROM AUTHOR]