Abstract
High dietary potassium (K+ ) intake dephosphorylates and inactivates the NaCl cotransporter (NCC) in the renal distal convoluted tubule (DCT). Using several ex vivo models, we show that physiological changes in extracellular K+ , similar to those occurring after a K+ rich diet, are sufficient to promote a very rapid dephosphorylation of NCC in native DCT cells. Although the increase of NCC phosphorylation upon decreased extracellular K+ appears to depend on cellular Cl- fluxes, the rapid NCC dephosphorylation in response to increased extracellular K+ is not Cl- -dependent. The Cl- -dependent pathway involves the SPAK/OSR1 kinases, whereas the Cl- independent pathway may include additional signalling cascades. A high dietary potassium (K+ ) intake causes a rapid dephosphorylation, and hence inactivation, of the thiazide-sensitive NaCl cotransporter (NCC) in the renal distal convoluted tubule (DCT). Based on experiments in heterologous expression systems, it was proposed that changes in extracellular K+ concentration ([K+ ]ex ) modulate NCC phosphorylation via a Cl- -dependent modulation of the with no lysine (K) kinases (WNK)-STE20/SPS-1-44 related proline-alanine-rich protein kinase (SPAK)/oxidative stress-related kinase (OSR1) kinase pathway. We used the isolated perfused mouse kidney technique and ex vivo preparations of mouse kidney slices to test the physiological relevance of this model on native DCT. We demonstrate that NCC phosphorylation inversely correlates with [K+ ]ex , with the most prominent effects occurring around physiological plasma [K+ ]. Cellular Cl- conductances and the kinases SPAK/OSR1 are involved in the phosphorylation of NCC under low [K+ ]ex . However, NCC dephosphorylation triggered by high [K+ ]ex is neither blocked by removing extracellular Cl- , nor by the Cl- channel blocker 4,4'-diisothiocyano-2,2'-stilbenedisulphonic acid. The response to [K+ ]ex on a low extracellular chloride concentration is also independent of significant changes in SPAK/OSR1 phosphorylation. Thus, in the native DCT, [K+ ]ex directly and rapidly controls NCC phosphorylation by Cl- -dependent and independent pathways that involve the kinases SPAK/OSR1 and a yet unidentified additional signalling mechanism.
Highlights
A high dietary potassium (K+) intake has antihypertensive effects and improves cardiovascular outcomes (Mente et al, 2014; O’Donnell et al, 2014)
Small variations of plasma [K+] rapidly modulate NaCl cotransporter (NCC) phosphorylation In previous experiments in mice, we found that oral K+ loading rapidly increases plasma [K+] and dephosphorylates NCC (Sorensen et al, 2013)
Consistent with previous in vivo data (Sorensen et al, 2013; Rengarajan et al, 2014; Terker et al, 2015), the effect of K+ on the isolated perfused kidney ex vivo was specific for NCC since the phosphorylation of the closely related transporter NKCC2 in the thick ascending limb of the Loop of Henle (TAL) remained stable, regardless of [K+] (Fig 1G)
Summary
A high dietary potassium (K+) intake has antihypertensive effects and improves cardiovascular outcomes (Mente et al, 2014; O’Donnell et al, 2014). These beneficial effects of a K+ rich diet are likely related to a negative Na+ balance due to an enhanced renal Na+ excretion (Sorensen et al, 2013; Mente et al, 2014; Buendia et al, 2015; Penton et al, 2015). Dietary K+ restriction increases NCC phosphorylation (Vallon et al, 2009) and cell surface abundance of NCC (Frindt & Palmer, 2010), and promotes a salt-sensitive rise in blood pressure (Vitzthum et al, 2014) that depends on the presence of NCC (Terker et al, 2015). Genetic diseases in which loss-of–function mutations in NCC and mutations in NCCregulating kinases (With no Lysine (K) (WNK) WNK1 and WNK4) and ubiquitin-protein ligase complexes (KLHL3, cullin) cause hypotension and hypertension, respectively (Simon et al, 1996; Wilson et al, 2001)
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