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Lack of adenylyl cyclase 6 induces alkalosis and enhances urinary acidification
Author(s) -
Poulsen Søren Brandt,
Fenton Robert A,
Rieg Timo
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.741.6
Subject(s) - pendrin , chemistry , medicine , endocrinology , adenylyl cyclase , bicarbonate , alkalosis , intercalated cell , biology , biochemistry , signal transduction , kidney , acidosis , transporter , gene
Adenylyl cyclase isoform 6 (AC6) is expressed along the entire nephron, catalyzes the synthesis of cyclic adenosine monophosphate (cAMP) and contributes to the regulation of various aspects of renal transport. Recent in vitro and ex vivo studies identified that cAMP regulates Cl − /HCO 3 − exchanger (pendrin) trafficking to the apical plasma membrane of type B intercalated cells. However, the isoforms of AC involved in the regulation of urinary pH are not known. To gain insight in this regard, we studied AC6 knockout (AC6 −/− ) and littermate wild‐type (WT) mice. As a model of metabolic alkalosis and to test for a defect in urinary alkalinization, mice were supplied sodium‐bicarbonate in their drinking water for 8 days. Baseline urinary pH was significantly lower in AC6 −/− mice (AC6 −/− : 6.5 ± 0.2; WT: 7.7 ± 0.2, P < 0.05), which was associated with a more alkaline blood pH (AC6 −/− : 7.44 ± 0.01; WT: 7.41 ± 0.01, P < 0.05). While blood pH was unaffected in both genotypes after bicarbonate administration compared to baseline conditions, urinary pH was increased in AC6 −/− mice during bicarbonate administration, and pendrin abundance was higher compared to WT mice (AC6 −/− : 225 ± 16%; WT: 100 ± 6%, P < 0.001). Immunohistochemistry showed a comparable subcellular pendrin distribution and number of pendrin‐positive cells/mm 2 cortex in AC6 −/− compared to WT mice (AC6 −/− : 121.2 ± 8.7; WT: 108.3 ± 6.6, NS), thus possibly indicating intact pendrin regulation. Proton pump (H + ‐ATPase B1 subunit) abundance was higher in AC6 −/− mice both under baseline conditions (AC6 −/− : 175 ± 25 %; WT: 100 ± 7%, P < 0.05) and after bicarbonate administration (AC6 −/− : 196 ± 16%; WT: 100 ± 15%, P < 0.01). Furthermore, the number of H + ‐ATPase B1 subunit‐positive cells/mm 2 was higher after bicarbonate administration both in the cortex/outer stripe outer medulla (AC6 −/− : 192.8 ± 10.5; WT: 161.0 ± 9.3, P < 0.05) and in the inner stripe outer medulla (AC6 −/− : 312.6 ± 23.5; WT: 224.1 ± 11.3, P < 0.01). In conclusion, our results suggest that lack of AC6 induces mild metabolic alkalosis and enhances urinary acidification under baseline conditions. Stable blood pH after alkaline loading in AC6 −/− may require a higher pendrin and H + ‐ATPase B1 subunit abundance. Support or Funding Information This work was supported by the O'Brien Center for Acute Kidney Injury Research Grant P30DK079337, Diabetes Endocrinology Research Center P30DK063491, American Heart Association 15BGIA22410018, Satellite Healthcare (a not‐for‐profit renal care provider), Department of Veterans Affairs Merit Review Award, and Center on Genetics of Transport and Epithelial Biology at University of Cincinnati. Further funding is provided by the Lundbeck Foundation, the Danish Medical Research Council, and the Novo Nordisk Foundation.