Atrial natriuretic peptide-stimulated Ca2+ reabsorption in rabbit kidney requires membrane-targeted, cGMP-dependent protein kinase type II

Atrial natriuretic peptide (ANP) and nitric oxide (NO) are key regulators o f ion and water transport in the kidney. Here, we report that these cGMP-el evating hormones stimulate Ca2+ reabsorption via a novel mechanism specific ally involving type II cGMP-dependent protein kinase (cGK II). ANP and the NO donor, sodium nitroprusside (SNP), markedly increased Ca2+ uptake in fre shly immunodissected rabbit connecting tubules (CNT) and cortical collectin g ducts (CCD). Although readily increasing cGMP, ANP and SNP did not affect Ca2+ and Na+ reabsorption in primary cultures of these segments. Immunoblo t analysis demonstrated that cGK II, and not cGK I, was present in freshly isolated CNT and CCD but underwent a complete down-regulation during the pr imary cell culture. However, upon adenoviral reexpression of cGK II in prim ary cultures, ANP, SNP, and 8-Br-cGMP readily increased Ca2+ reabsorption. In contrast, no cGMP-dependent effect on electrogenic Na+ transport was obs erved. The membrane localization of cGK II proved to be crucial for its act ion, because a nonmyristoylated cGK II mutant that was shown to be localize d in the cytosol failed to mediate ANP-stimulated Ca2+ transport. The Ca2+- regulatory function of cGK II appeared isotype-specific because no cGMP-med iated increase in Ca2+ transport was observed after expression of the cytos olic cGK IP or a membrane-bound cGK II/I beta chimer. These results demonst rate that ANP- and NO-stimulated Ca2+ reabsorption requires membrane-target ed cGK II.