Role of adrenomedullin in mediating water reabsorption in rat inner medullary collecting ducts

Abstract

Adrenomedullin (ADM) increases water permeability in the inner medullary collecting duct by mediating aquaporin‐2 (AQP2) phosphorylation. It is generally considered to be a backup system for vasopressin. We investigated whether adrenomedullin stimulates osmotic water permeability through cAMP and/or protein kinase A (PKA). RNA sequencing and western analysis showed that ADM and its receptors, calcitonin‐receptor‐like receptor (CRLR) and receptor‐activity‐modifying proteins 2 or 3 (RAMP2 or RAMP3) are highly expressed in the inner medullary collecting ducts of control rats. No mRNA expression was seen for RAMP1. We measured water permeability in inner medullary collecting ducts of rats by tubule perfusion with and without treatment with the PDE4 inhibitor roflumilast or the PKA inhibitor H89. ADM significantly increased osmotic water permeability from 251.4 ± 58.1 to 383.4 ± 73.2 μm/s (n=4, p<0.05). Roflumilast (30nM) further increased ADM‐stimulated osmotic water permeability to 472.7 ± 84.9 μm/s (n=4, p<0.05). Inhibition of PKA by H89 decreased ADM‐stimulated osmotic water permeability from 225.4 ± 57.3 to 179.7 ± 49.6 μm/s (n=3, p<0.05). Western analysis with phospho‐specific antibody showed that ADM significantly increased phosphorylation of AQP2 at serine 256 and decreased phosphorylation of AQP2 at serine 261. We conclude that ADM and its receptors are expressed in inner medulla and that the mechanism of ADM stimulation of water reabsorption involves cAMP and activation of PKA. Further, our results suggest that ADM may represent a complimentary method for vasopressin in regulating water homeostasis.Support or Funding InformationThis work was supported by Emory URC grant 00067457, and AHA Career Development Grant #18CDA34060053.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.