Atrial natriuretic peptide-stimulated Ca(2+) reabsorption in rabbit kidney requires membrane-targeted, cGMP-dependent protein kinase type II

Atrial natriuretic peptide (ANP) and nitric oxide (NO) are key regulators of ion and water transport in the kidney. Here, we report that these cGMP-elevating hormones stimulate Ca(2+) reabsorption via a novel mechanism specifically involving type II cGMP-dependent protein kinase (cGK II). ANP and the NO donor, sodium nitroprusside (SNP), markedly increased Ca(2+) uptake in freshly immunodissected rabbit connecting tubules (CNT) and cortical collecting ducts (CCD). Although readily increasing cGMP, ANP and SNP did not affect Ca(2+) and Na(+) reabsorption in primary cultures of these segments. Immunoblot 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 primary cell culture. However, upon adenoviral reexpression of cGK II in primary cultures, ANP, SNP, and 8-Br-cGMP readily increased Ca(2+) reabsorption. In contrast, no cGMP-dependent effect on electrogenic Na(+) transport was observed. The membrane localization of cGK II proved to be crucial for its action, because a nonmyristoylated cGK II mutant that was shown to be localized in the cytosol failed to mediate ANP-stimulated Ca(2+) transport. The Ca(2+)-regulatory function of cGK II appeared isotype-specific because no cGMP-mediated increase in Ca(2+) transport was observed after expression of the cytosolic cGK Iβ or a membrane-bound cGK II/Iβ chimer. These results demonstrate that ANP- and NO-stimulated Ca(2+) reabsorption requires membrane-targeted cGK II.