Evidence for beta-adrenoceptors in rat proximal convoluted tubules

It is well documented that renal catecholamines, acting as paracrine or autocrine substances, modulate reabsorption of sodium and other substances in renal tubules. However, beta-receptors or the resulting stimulation of adenylate cyclase (AC) have not been measured directly in the proximal convoluted tubules (PCT) of mammalian kidney. In this study, the beta adrenergic receptors in the PCT from rat kidney were characterized pharmacologically by measuring agonist stimulated adenylate cyclase activity. Isoproterenol (ISO) (10 microM) significantly increased AC activity in the microdissected PCT (ISO, 193.0 +/- 23.6 vs basal, 118.7 +/- 14.3 fmol/mm/20; n = 8, p = 0.004). The stimulation of AC in PCT by ISO was blocked by 10 microM propranolol (p < 0.01); it was also blocked by either the beta-1-adrenergic blocker, 10 microM atenolol (p < 0.05), or the beta-2-adrenergic blocker, 10 microM ICI-118551 (p < 0.05). The beta adrenergic receptor binding sites were localized by autoradiography; specific [125I] iodocyanopindolol ([125I] ICYP) binding could be measured in the microdissected rat PCT. In conclusion, these findings provide evidence for beta adrenergic receptors in the PCT in rat kidney by radioligand binding and beta adrenergic agonist stimulated AC activity.