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Aim Maintenance of the blood and extracellular volume requires tight control of endothelial macromolecule permeability, which is regulated by c AMP signalling. This study probes the role of the c AMP mediators rap guanine nucleotide exchange factor 3 and 4 (Epac1 and Epac2) for in vivo control of microvascular macromolecule permeability under basal conditions. Methods Epac1−/− and Epac2−/− C57 BL /6J mice were produced and compared with wild-type mice for transvascular flux of radio-labelled albumin in skin, adipose tissue, intestine, heart and skeletal muscle. The transvascular leakage was also studied by dynamic contrast-enhanced magnetic resonance imaging ( DCE- MRI) using the MRI contrast agent Gadomer-17 as probe. Results Epac1−/− mice had constitutively increased transvascular macromolecule transport, indicating Epac1-dependent restriction of baseline permeability. In addition, Epac1−/− mice showed little or no enhancement of vascular permeability in response to atrial natriuretic peptide ( ANP), whether probed with labelled albumin or Gadomer-17. Epac2−/− and wild-type mice had similar basal and ANP-stimulated clearances. Ultrastructure analysis revealed that Epac1−/− microvascular interendothelial junctions had constitutively less junctional complex. Conclusion Epac1 exerts a tonic inhibition of in vivo basal microvascular permeability. The loss of this tonic action increases baseline permeability, presumably by reducing the interendothelial permeability resistance. Part of the action of ANP to increase permeability in wild-type microvessels may involve inhibition of the basal Epac1-dependent activity. [ABSTRACT FROM AUTHOR]

Today, there is evidence that the cAMP-dependent kinases (PKA) are not the only intracellular receptors involved in intracellular cAMP signalling in eukaryotes. Other cAMP-binding proteins have been recently identified, including some cyclic nucleotide-gated channels and Epac (exchange protein directly activated by cAMP) proteins. All these proteins bind cAMP through conserved cyclic nucleotide monophosphate-binding domains. However, all putative cAMP-binding proteins having such domains, as revealed by computer analysis, do not necessarily bind cAMP, indicating that their presence is not a sufficient criteria to predict cAMP-binding property for a protein. [Copyright &y& Elsevier]

Aim: The cAMP-mediator Epac1 (RapGef3) has high renal expression. Preliminary observations revealed increased diuresis in Epac1 -/- mice. We hypothesized that Epac1 could restrict diuresis by promoting transcellular collecting duct (CD) water and urea transport or by stabilizing CD paracellular junctions to reduce osmolyte loss from the renal papillary interstitium., Methods: In Epac1 -/- and Wt C57BL/6J mice, renal papillae, dissected from snap-frozen kidneys, were assayed for the content of key osmolytes. Cell junctions were analysed by transmission electron microscopy. Urea transport integrity was evaluated by urea loading with 40% protein diet, endogenous vasopressin production was manipulated by intragastric water loading and moderate dehydration and vasopressin type 2 receptors were stimulated selectively by i.p.-injected desmopressin (dDAVP). Glomerular filtration rate (GFR) was estimated as [ 14 C]inulin clearance. The glomerular filtration barrier was evaluated by urinary albumin excretion and microvascular leakage by the renal content of time-spaced intravenously injected 125 I- and 131 I-labelled albumin., Results: Epac1 -/- mice had increased diuresis and increased free water clearance under antidiuretic conditions. They had shorter and less dense CD tight junction (TJs) and attenuated corticomedullary osmotic gradient. Epac1 -/- mice had no increased protein diet-induced urea-dependent osmotic diuresis, and expressed Wt levels of aquaporin-2 (AQP-2) and urea transporter A1/3 (UT-A1/3). Epac1 -/- mice had no urinary albumin leakage and unaltered renal microvascular albumin extravasation. Their GFR was moderately increased, unless when treated with furosemide., Conclusion: Our results conform to the hypothesis that Epac1-dependent mechanisms protect against diabetes insipidus by maintaining renal papillary osmolarity and the integrity of CD TJs., (© 2020 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)