Immunofluorescent imaging of β1- and β2-adrenergic receptors in rat kidney

Abstract

Background. β-Adrenergic receptors (β-ARs) are known to participate in the regulation of glomerular filtration, NaCl reabsorption, acid-base balance, and renin secretion; however, the precise histologic localization of β-AR at putative signaling sites involved in these processes remains an open issue. Methods. We used a set of subtype-specific rabbit antibodies to visualize β1 and β2-AR in rat kidney by immunohistochemistry and specified cells and segments of the nephron thought to be regulated by catecholamines. In addition, the relative proportion of β-AR subtypes in cortical and medullary portions of rat kidney was determined by Western blotting and by competing [125I]-cyanopindolol binding with the β1- or β2-selective antagonists bisoprolol or ICI 118,551, respectively. Results. Immunoreactivity for β1-AR was found in mesangial cells, juxtaglomerular granular cells, the macula densa epithelium, proximal and distal tubular segments, and acid-secreting type A intercalated cells of the cortical and medullary collecting ducts. Immunoreactivity for β2-AR was predominantly localized in the apical and subapical compartment of proximal and, to a lesser extent, distal tubular epithelia (suggesting interactions with luminal fluid catecholamines). Both subtypes were dense in the membranes of smooth muscle cells from renal arteries. Concordant data were obtained by radioligand binding and immunoblotting of membranes prepared from cortical and medullary portions of the kidney. Conclusion. Our data provide an immunohistochemical basis for the cellular targets of β-adrenergic regulation of renal function. Moreover, they could help to devise therapeutic strategies directed at renal β-ARs.