Calcineurin inhibitors block sodium-chloride cotransporter dephosphorylation in response to high potassium intake

Abstract

Dietary potassium intake is inversely related to blood pressure and mortality. Moreover, the sodium-chloride cotransporter (NCC) plays an important role in blood pressure regulation and urinary potassium excretion in response to potassium intake. Previously, it was shown that NCC is activated by the WNK4-SPAK cascade and dephosphorylated by protein phosphatase. However, the mechanism of NCC regulation with acute potassium intake is still unclear. To identify the molecular mechanism of NCC regulation in response to potassium intake, we used adult C57BL/6 mice fed a 1.7% potassium solution by oral gavage. We confirmed that acute potassium load rapidly dephosphorylated NCC, which was not dependent on the accompanying anions. Mice were treated with tacrolimus (calcineurin inhibitor) and W7 (calmodulin inhibitor) before the oral potassium loads. Dephosphorylation of NCC induced by potassium was significantly inhibited by both tacrolimus and W7 treatment. There was no significant difference in WNK4, OSR1, and SPAK expression after high potassium intake, even after tacrolimus and W7 treatment. Another phosphatase, protein phosphatase 1, and its endogenous inhibitor I-1 did not show a significant change after potassium intake. Hyperkaliuria, induced by high potassium intake, was significantly suppressed by tacrolimus treatment. Thus, calcineurin is activated by an acute potassium load, which rapidly dephosphorylates NCC, leading to increased urinary potassium excretion.

NaCl cotransporter abundance in urinary vesicles is increased by calcineurin inhibitors and predicts thiazide sensitivity

“…Recently, it was demonstrated in mice that treatment with Tac prevents the acute high potassium induced NCC dephosphorylation, while tNCC remained unaffected [24]. In contrast to previous studies, this acute regulatory system mediated by calcineurin is shown to be independent of the WNK-SPAK signaling cascade [24]. Our study demonstrated that chronic administration of CNIs increases the abundance of both tNCC and pNCC in uEVs of kidney transplant recipients.…”

“…[23] in mDCT cells treated with CsA. Recently, it was demonstrated in mice that treatment with Tac prevents the acute high potassium induced NCC dephosphorylation, while tNCC remained unaffected [24]. In contrast to previous studies, this acute regulatory system mediated by calcineurin is shown to be independent of the WNK-SPAK signaling cascade [24].…”

“…revealed that Tac-induced hypertension in mice is predominantly mediated by an increase in pNCC abundance, possibly through an effect of the NCC-regulating kinases WNK3, WNK4, and STE20/SPS1-related proline/alanine-rich kinase (SPAK) [21]. Recent evidence suggests that in mice, Tac prevents the high potassium stimulated NCC dephosphorylation [24]. Additionally, it has been demonstrated that Tac acts directly on kidney tubule cells expressing NCC to cause hypertension, and that inhibition of calcineurin is required for this effect [22].…”

Protein Phosphatase 1 Inhibitor–1 Mediates the cAMP-Dependent Stimulation of the Renal NaCl Cotransporter

“…In Xenopus laevis oocytes, heterologous co-expression of NCC with PP4 lowered NCC phosphorylation 17 . Likewise, pharmacological inhibition of PP1 with calyculin A 18 and of PP3 with tacrolimus 19,20 increased NCC phosphorylation in various experimental settings. The stimulatory effect of PP3 inhibition on NCC may have important clinical implications.…”

Potassium acts through mTOR to regulate its own secretion

“…Na + and Clare reabsorbed together in an electroneutral fashion in this nephron segment by the sodium chloride cotransporter (NCC) (15). Its inhibition allows more Na + to pass to tubular segments further downstream where ENaC-mediated Na + reabsorption establishes the lumen negative potential driving K + secretion (12,16,17). However, pharmacologic inhibition of NCC is insufficient to enhance K + excretion, despite a marked increase in Na + delivery to the ASDN (18,19); this stands in marked contrast to a KCl load, which rapidly stimulates both natriuresis and marked kaliuresis (12,20).…”