Abstract
Adrenomedullin (ADM) is a vasodilator that causes natriuresis and diuresis. However, the direct effect of ADM on osmotic water permeability in the rat inner medullary collecting duct (IMCD) has not been tested. We investigated whether ADM and its ADM receptor components (CRLR, RAMP2, and 3) are expressed in rat inner medulla (IM) and whether ADM regulates osmotic water permeability in isolated perfused rat IMCDs. The mRNAs of ADM, CRLR, and RAMP2 and 3 were detected in rat IM. Abundant protein of CRLR and RAMP3 were also seen but RAMP2 protein level was extremely low. Adding ADM (100 nM) to the bath significantly decreased osmotic water permeability. ADM significantly decreased aquaporin-2 (AQP2) phosphorylation at Serine 256 (pS256) and increased it at Serine 261 (pS261). ADM significantly increased cAMP levels in IM. However, inhibition of cAMP by SQ22536 further decreased ADM-attenuated osmotic water permeability. Stimulation of cAMP by roflumilast increased ADM-attenuated osmotic water permeability. Previous studies show that ADM also stimulates phospholipase C (PLC) pathways including protein kinase C (PKC) and cGMP. We tested whether PLC pathways regulate ADM-attenuated osmotic water permeability. Blockade of either PLC by U73122 or PKC by rottlerin significantly augmented the ADM-attenuated osmotic water permeability and promoted pS256-AQP2 but did change pS261-AQP2. Inhibition of cGMP by L-NAME did not change AQP2 phosphorylation. In conclusion, ADM primarily binds to the CRLR-RAMP3 receptor to initiate signaling pathways in the IM. ADM reduced water reabsorption through a PLC-pathway involving PKC. ADM-attenuated water reabsorption may be related to decreased trafficking of AQP2 to the plasma membrane. cAMP is not involved in ADM-attenuated osmotic water permeability.
Highlights
Adrenomedullin (ADM) is a vasodilator peptide first extracted from human pheochromocytoma tissue in 1993 [1]
Since ADM can activate cyclic adenosine monophosphate (cAMP), phospholipase C (PLC), cGMP, and protein kinase C (PKC), we investigated whether these signaling molecules are involved in the regulation of ADM-mediated osmotic water permeability
AQP2 was used as inner medullary collecting duct (IMCD) marker, AQP1 as thin descending limb marker
Summary
Adrenomedullin (ADM) is a vasodilator peptide first extracted from human pheochromocytoma tissue in 1993 [1]. Data from Leclerc et al show that ADM increases sodium reabsorption in rabbit distal tubules [15], which suggests a subsequent increase in water reabsorption These paradoxical findings suggest that further investigation needs to be performed to clarify the effect of ADM on fluid and electrolyte homeostasis in renal tubules. We investigated whether ADM affects osmotic water permeability in rat IMCDs. Since ADM can activate cAMP, PLC, cGMP, and PKC, we investigated whether these signaling molecules are involved in the regulation of ADM-mediated osmotic water permeability. Since ADM can activate cAMP, PLC, cGMP, and PKC, we investigated whether these signaling molecules are involved in the regulation of ADM-mediated osmotic water permeability
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