Effect of dietary K intake on apical small-conductance K channel in CCD: role of protein tyrosine kinase

Abstract

We have used Western blot to examine the expression of cSrc protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP)-1D in the renal cortex, and the patch-clamp technique to determine the role of PTK in mediating the effect of dietary K intake on the small-conductance K (SK) channel in the cortical collecting duct (CCD). When rats were on a K-deficient (KD) diet for 1, 3, 5, and 7 days, the expression of cSrc increased by 40, 90, 140, and 135%, respectively. In contrast, the expression of cSrc in the renal cortex from rats on a high-K (HK) diet for 1, 2, and 3 days decreased by 40, 60, and 75%, respectively. However, the protein level of PTP-1D was not significantly changed by dietary K intake. The addition of 1 microM herbimycin A increased NP(o), a product of channel number (N) and open probability (P(o)) in the CCD from rats on a normal diet or on a KD diet. The increase in NP(o) was 0.30 (normal), 0.45 (1-day KD), 0.65 (3-day KD), 1.55 (5-day KD), and 1.85 (7-day KD), respectively. Treatment of the CCD with herbimycin A from rats on a KD diet increased NP(o) per patch from the control value (0.7) to 1.4 (1-day KD), 1.6 (3-day KD), 2.6 (5-day KD), and 3.5 (7-day KD), respectively. In contrast, HK intake for as short as 1 day abolished the effect of herbimycin A. Furthermore, the expression of ROMK channels in the renal cortex was the same between rats on a KD diet or on a HK diet. Moreover, treatment with herbimycin A did not further increase NP(o) in the CCDs from rats on a HK diet. We conclude that dietary K intake plays a key role in regulating the activity of the SK channels and that PTK is involved in mediating the effect of the K intake on channel activity in the CCD.

WNK1 kinase isoform switch regulates renal potassium excretion

“…Sprague-Dawley rats were fed matched diets that were either deficient in K (low-K diet) or high in K content (high-K diet) for 2 days and compared with control (control-K diet). These diets are well established to change Kir1.1 channel density and provoke strong K conservation (low-K diet) or strikingly increased renal K excretion (high-K diet) compared with animals on a control-K diet (22)(23)(24)(25). Quantitative analysis of mRNA levels from the kidneys of these animals using isoform-specific Kir1.1 protein abundance in the presence and absence of WNK1 isoforms.…”

Inhibitor of growth 4 (ING4) is up-regulated by a low K intake and suppresses renal outer medullary K channels (ROMK) by MAPK stimulation

“…The inhibitory effect of low K intake on renal K secretion is partially achieved by removing renal outer medullary potassium (ROMK)-like small conductance K channels from the apical membrane of principal cells in the cortical collecting duct (CCD) through a protein-tyrosine kinase (PTK)-dependent mechanism (3). We have demonstrated previously that low K intake stimulates the production of superoxide anions and its related products, which in turn increase PTK expression and activity (4,5).…”

Inhibition of phosphatidylinositol 3-kinase stimulates activity of the small-conductance K channel in the CCD

“…Factors such as dietary K intake play a key role in regulating channel activity in the CCD (11,32): high K intake increases, whereas low K intake decreases, SK channel activity in the CCD. We have previously demonstrated that low K intake stimulates the expression of Src family protein tyrosine kinase (PTK) and that inhibition of PTK increases SK channel activity (33,34). However, detailed mechanisms by which PTK-dependent signal transduction pathways regulate ROMK channel activity are still not completely understood.…”