Thromboxane receptors in human kidney tissues

Thromboxane (TX) A(2) effects in the-kidneys include contraction of glomerular mesangial cells and intrarenal vascular tissue. A kidney cDNA encoding a TX receptor expressed in rat renal glomeruli and rat renal arterial smooth muscle cells has been reported. However, TXA(2) receptors in human kidneys have not been documented. The purpose of this study was to identify and characterize TXA(2) receptors in glomeruli and intrarenal arteries isolated from human kidneys. Normal kidneys, not used for transplant because of technical reasons, were kept at -70 degrees C and used for research purposes. The glomeruli and intrarenal arteries were isolated from renal cortical tissue by a mechanical sieving technique. The equilibrium dissociation constant and receptor number were determined by nonlinear analysis of binding inhibition data. The data were generated in radioreceptor assays using [I-125]-BOP, a stable analog of TXA(2). The dissociation constants (mean +/- SEM) for binding of I-BOP to human glomeruli and intrarenal arterial membranes were 6.6 +/- 1.1 nM (n = 7) and 20 +/- 6 nM (n = 7), respectively (p < 0.05). The receptor number was 311 +/- 91 fmol/mg protein (n = 7) in glomeruli and 74 +/- 16 fmol/mg protein (n = 7) in intrarenal arterial membranes (p < 0.04). The order of specificity of TXA(2) analogs for [I-125]-BOP binding sites was similar in glomeruli and in arterial membranes and was I-BOP greater than or equal to U46619 greater than or equal to pinane TXA(2) greater than or equal to carbocyclic TXA(2) greater than or equal to PGH(2). These findings provide direct evidence for the presence of specific, high-affinity [I-125]-BOP binding sites in human renal glomeruli and extraglomerular vascular tissue. These data also indicate that the human binding sites have higher affinity for the TXA(2) agonist I-BOP than for PGH(2). (C) 1999 Elsevier Science Inc. All rights reserved.