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1 Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands
2 Department of Physiological Chemistry and Centre for Biomedical Genetics, University Medical Centre Utrecht, Utrecht, Netherlands
3 Department of Pathology, Leiden University Medical Center, Leiden, Netherlands
* To whom correspondence should be addressed. E-mail: p.deen{at}ncmls.ru.nl.
In the kidney, many physiological processes of ion transport and cellular proliferation are mediated via cAMP, which classically activates protein kinase A (PKA). Recently, however, two new cAMP targets, the exchange protein directly activated by cAMP (Epac) 1 and 2 were identified, which mediate alternative pathways to PKA. To investigate their renal expression, antibodies specifically recognizing Epac1 and Epac2 were generated and used in rat immunohistochemistry with antibodies recognizing Aquaporin-1, Tamm-Horsfall protein, Calbindin-D28K and aquaporin-2 to mark proximal tubules(PT)/thin descending limbs of Henles loop(tDLH), thick ascending limbs of Henles loop (TAL), distal convoluted tubule/connecting tubule (DCT/CNT), and the collecting duct (CD) principal cells, respectively. Epac1 and Epac2 were expressed at the brush border of PT cells, but were absent from tDLH cells. In the TAL, Epac1 and Epac2 were expressed throughout the cells with some confinement towards the apical membrane. In the DCT/CNT, Epac1 was confined to the apical region of the cells, whereas Epac2 was mainly expressed in the apical and basolateral regions. In the CD, a dispersed Epac1 expression was found in intercalated cells only (CCD), principal and intercalated cells (OMCD), and mainly AQP2-negative cells in the IMCD. In contrast, Epac2 expression was at the apical and basolateral membrane of cortical principal cells, dispersed and apical in the OMCD, and in all cells of the IMCD. A similar distribution for Epac1/2 was found in the human kidney. The observed expression in different tubular segments suggests a major role for Epac 1/2 in tubular transport physiology and cellular proliferation.
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