Increased shear stress-released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons

Increased shear stress–released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons. Background Nitric oxide is an important vasodilator released from endothelial cells by the calcium-dependent endothelial nitric oxide synthase (NOS). We considered it important to investigate how shear stress/perfusion pressure influenced endothelial cell calcium concentration, nitric oxide release, and autoregulation of the afferent arteriole, since this arteriole controls glomerular filtration rate (GFR) and renin release Methods We used an isolated perfused juxtamedullary nephron preparation and measured calcium with Fura 2, nitric oxide with 4-amino-5 methylamino-2′, 7′-difluorescein (DAF-FM) and diameter with an imaging system. A mathematical model was applied to calculate changes in nitric oxide concentration and shear stress/wall tension during perfusion with and without erythrocytes at perfusion pressures varying from 50 to 150mm Hg. Result Cell-free perfusion increased nitric oxide concentration and abolished autoregulation; addition of erythrocytes or l-arginine analog N-nitro-l-arginine methyl ester (L-NAME) decreased nitric oxide concentration and reinstated autoregulation. Elevated perfusion pressure/elevated shear stress increased nitric oxide release and surprisingly decreased the endothelial cell calcium concentration, with perfusion pressure increase from 50 to 150mm Hg, using blood perfusion endothelial calcium concentration decreased from 186 ± 39 to 76 ± 25nmol/L and with cell-free perfusion from 116 ± 33 to 56 ± 21nmol/L. Conclusion Nitric oxide scavenging by erythrocytes has a high impact on arteriolar nitric oxide concentration and autoregulatory response. Nitric oxide measurements in endothelial cells of the afferent arteriole showed that increased perfusion pressure/shear stress increased nitric oxide release, while simultaneously endothelial cell calcium concentration decreased, possibly indicating a feedback control of this calcium by nitric oxide release.