[Characterization of thromboxane A2 receptors in rat kidney]

The renal TXA2 receptors were investigated in preparations derived from rat kidney. Perfused rat kidneys were removed and separated into cortex and medulla. Each subcellular fraction was prepared by a sucrose density gradient method for analyzing the subcellular distribution of TXA2 receptors. The membranes were obtained by 40,000 x g centrifugation for analyzing the renal distribution of TXA2 receptors. Bindings of [3H]SQ 29548, a TXA2 receptor antagonist, to these preparations were carried out using a filtration method. Furthermore, the binding of [3H]SQ 29548 to membranes from rat kidney cortex was compared with its binding to rat washed platelets. The membrane fraction had the highest density of TXA2 receptors among subcellular fractions determined. TXA2 receptors appeared in corticomedullary junction with high density. Scatchard analysis using [3H]SQ 29548 as a ligand revealed a single binding site of TXA2 receptors in membranes from rat kidney cortex, and the dissociation constant (Kd) was remarkably higher than the Kd in rat washed platelets. These findings suggest that TXA2 receptors in membranes from rat kidney cortex are different from those in rat platelets, and TXA2 receptor activation in kidney might play a role in renal function.