Decrease in dietary K intake stimulates the generation of superoxide anions in the kidney and inhibits K secretory channels in the CCD

Abstract

We previously demonstrated that K depletion inhibited ROMK-like small-conductance K channels (SK) in the cortical collecting duct (CCD) and that the effect was mediated by superoxide anions that stimulated Src family protein tyrosine kinase (PTK) and mitogen-activated protein kinase (MAPK) (51). However, because animals on a K-deficient diet had a severe hypokalemia, superoxide-dependent signaling may not regulate ROMK channels under physiological conditions with a normal plasma K concentration. In the present study, we used the patch-clamp technique and Western blot to examine the effect of a moderate K restriction on ROMK-like SK channels and the role of PTK and MAPK in regulating apical K channels in the CCD of animals on a low-K diet (LK; 0.1% K). Rats and mice fed a LK diet for 7 days had a normal plasma K concentration. However, a LK intake increased the expression of angiotensin II type 1 receptor in the kidney. Moreover, patch-clamp experiments demonstrated that LK intake decreased the probability finding SK channels and channel activity defined by NPo (a product of channel number and open probability) in the CCD of both rat and mouse kidneys. Also, LK intake significantly stimulated the production of superoxide anions in the renal cortex and outer medulla in both rats and mice and increased superoxide level in the rat CCD. Moreover, LK intake augments the phosphorylation of p38 and ERK MAPK, the expression of c-Src and tyrosine phosphorylation of ROMK channels. However, treatment of animals with tempol abolished the effect of LK intake on MAPK and c-Src and increased ROMK channel activity in comparing with those of nontreated rats on a LK diet. Inhibiting p38 and ERK with SB202190 and PD98059 significantly stimulated SK in the CCD in rats on a LK diet. In addition, inhibition of PTK with herbimycin A activated SK channels in the CCD from rats on a LK diet. We conclude that LK intake stimulates the generation of superoxide anion and related products and that MAPK and Src family PTK play a physiological role in inhibiting apical K channels in the principal cells in response to LK intake. Ca 2ϩ -activated BK channel; ROMK (Kiy1-1); renal K secretion; K homeostasis A DECREASE IN THE DIETARY K intake suppresses renal K secretion (41,43,53). K restriction-induced decrease in renal K secretion is achieved by both inhibition of apical ROMK-like small-conductance K channels (SK) and Ca 2ϩ -activated big conductance K channel (BK) channels in principal cell (PC) and by stimulating K absorption through K-H-ATPase in intercalated cell (IC) (57,58). Several studies demonstrated that K restriction inhibits ROMK-like SK channels by stimulating endocytosis (12,55,56). Although the mechanism by which K restriction inhibits ROMK channels is not completely understood, WNK (with-no-lysine kinase) and superoxide anions play an important role in mediating endocytosis (27, 51). WNK1, 3, and 4 have been shown to be expressed in the cortical collecting duct (CCD) and inhibit ROMK channels by stimulating a clathrin-dependent pat...

Regulation of Transport in the Connecting Tubule and Cortical Collecting Duct

“…Immunohistochemical analysis shows that ROMK channels are specifically localized to the apical membrane of the epithelial cells (291, 396, 655, 658). Electrophysiological studies confirmed apical localization of ROMK channels (164, 167, 323, 325, 620, 627). K + channel activity was absent in the apical membranes of either TAL or CCD of ROMK −/− mice (342).…”

The Angiotensin II Type 1 Receptor-Associated Protein Attenuates Angiotensin II-Mediated Inhibition of the Renal Outer Medullary Potassium Channel in Collecting Duct Cells

“…Although p38 and ERK1/2 pathways seem to be part of AT1Rdependent inhibition of ROMK channels during LK diets (Babilonia et al, 2006;Jin et al, 2009), tyrosine phosphorylation of ROMK by c-Src is the most important signaling pathway directly responsible for ROMK inhibition during potassium restriction. While collecting ducts from rats fed LK diets do not show relevant ROMK-like small conductance K + currents, these same collecting ducts presented a significant increase in the number of ROMK-like channels in patch-clamp recordings when the collecting duct cells were acutely treated with c-Src inhibitor herbimicyn A for 30 min, an effect that does not occur in rats receiving HK diets (Wang et al, 2000(Wang et al, , 2010. Also, in the collecting ducts from animals receiving LK diets, the acute treatment with c-Src inhibitor herbymicin A majorly abolishes the Ang II inhibitory effect over ROMK activity (Wei et al, 2007).…”

Gut Sensing of Potassium Intake and its Role in Potassium Homeostasis

“…A recent study by this group further demonstrated that all of these changes occurred with normal plasma [K + ] in rats and mice maintained on a low (0.1%) K + diet (49). Our previous study also showed that modest K + deprivation increases PTK expression and ROMK phosphorylation in the absence of a fall in plasma K + or aldosterone levels (50).…”

“…Regarding this alternative, a strong candidate for such a factor is reactive oxygen species (ROS) including superoxide anions. As discussed above, Wang and colleagues have suggested that renal K + adaptation is mediated by changes in superoxide anion production in the kidneys, which occurred even with normal plasma [K + ] (48, 49). On the other hand, recent studies have suggested that ROS is involved in detrimental effects of low K + diet and protective effects of high K + diet on the cardiovascular system (63, 64).…”

“…With partial K + deprivation, plasma [K + ] may not fall even after an extended period of time, if dietary K + intake, although reduced, is sufficient to replenish the K + loss. Plasma [K + ] was normal in rats after 30 days of reducing K + intake to 1/3 of normal (50) or in rats and mice after a week on a 0.1% K + diet (49). In these cases, the second phase of adaptation may not occur.…”