SPAK-mediated NCC regulation in response to low-K⁺ diet

Abstract

The NaCl cotransporter (NCC) of the renal distal convoluted tubule is stimulated by low-K(+) diet by an unknown mechanism. Since recent work has shown that the STE20/SPS-1-related proline-alanine-rich protein kinase (SPAK) can function to stimulate NCC by phosphorylation of specific N-terminal sites, we investigated whether the NCC response to low-K(+) diet is mediated by SPAK. Using phospho-specific antibodies in Western blot and immunolocalization studies of wild-type and SPAK knockout (SPAK(-/-)) mice fed a low-K(+) or control diet for 4 days, we found that low-K(+) diet strongly increased total NCC expression and phosphorylation of NCC. This was associated with an increase in total SPAK expression in cortical homogenates and an increase in phosphorylation of SPAK at the S383 activation site. The increased pNCC in response to low-K(+) diet was blunted but not completely inhibited in SPAK(-/-) mice. These findings reveal that SPAK is an important mediator of the increased NCC activation by phosphorylation that occurs in the distal convoluted tubule in response to a low-K(+) diet, but other low-potassium-activated kinases are likely to be involved.

Potassium Supplementation Prevents Sodium Chloride Cotransporter Stimulation During Angiotensin II Hypertension

“…Wade and colleagues fed SPAK knockout mice a K + deficient diet and found that the NCC regulatory response was blunted but not eliminated, indicating that other kinases may play a role. 37 We found that, like NCC phosphorylation, the regulation of SPAK increased 50% during AngII infusion and was blunted by doubling dietary K + during AngII infusion but the response was more subtle: SPAKp was reduced to levels not different from baseline, nor different from the A1K group, and total SPAK remained at 50% above baseline. In our previous studies of AngII infused rats and mice, SPAK increased after only 3–4 days of AngII infusion, before there was any significant increase in ENaC subunit cleavage or blood pressure, 8, 38 which suggests that SPAK may be directly stimulated by AngII, 39 that is, before K + excretion is increased.…”

Mutant Cullin 3 causes familial hyperkalemic hypertension via dominant effects

“…Redistribution of WNK1, WNK4, and SPAK to larger intracellular puncta has been reported in several mouse models with lower plasma [K + ], including SPAK KOs (42,51,52), and mice fed low K + diets (43,44,51). Whether puncta form when mice are placed on a high [K + ] diet has not yet been reported, but they were observed in mice with targeted deletion of Cul3 exon 9, which have elevated plasma [K + ] (30).…”

Potassium: friend or foe?

“…These studies have focused on the abundance of total and apical NCC as well as NCC phosphorylation, since NCC phosphorylation increases transport of sodium chloride [23, 24]. A consistent finding has been that high dietary potassium inhibits NCC expression and phosphorylation [25–28], whereas low dietary potassium has the opposite effect, increasing NCC expression and phosphorylation [29, 30, 28, 31]. In fact, even a single oral potassium “meal” is sufficient to rapidly suppress NCC and increase urinary sodium excretion [32].…”

“…A low potassium diet increases WNK phosphorylation [36], as well as SPAK phosphorylation [36, 31, 28], which will increase NCC phosphorylation and activity.…”