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

“…Thus the PI3K-induced depletion of PIP 2 might tend to reduce channel activity. Li et al (14) reported that inhibition of PI3K stimulated ROMK-like K ϩ channel activity in rat cortical collecting duct. In contrast, PI3K inhibitors reduced channel activity in cultured human proximal tubule cells.…”

Section: Discussionmentioning

confidence: 99%

Delayed and acute effects of interferon-γ on activity of an inwardly rectifying K⁺ channel in cultured human proximal tubule cells

Nakamura

You²,

Kojo³

et al. 2009

American Journal of Physiology-Renal Physiology

View full text Add to dashboard Cite

ϩ channel in cultured human renal proximal tubule cells (RPTECs) is stimulated and inhibited by nitric oxide (NO) at low and high concentrations, respectively. In this study, we investigated the effects of IFN-␥, one of the cytokines which affect the expression of inducible NO synthase (iNOS), on intracellular NO and channel activity of RPTECs, using RT-PCR, NO imaging, and the cellattached mode of the patch-clamp technique. Prolonged incubation (24 h) of cells with IFN-␥ (20 ng/ml) enhanced iNOS mRNA expression and NO production. In these cells, a NOS inhibitor, N -nitro-L-arginine methyl ester (L-NAME; 100 M), elevated channel activity, suggesting that NO production was so high as to suppress the channel. This indicated that IFN-␥ would chronically suppress channel activity by enhancing NO production. Acute effects of IFN-␥ was also examined in control cells. Simple addition of IFN-␥ (20 ng/ml) to the bath acutely stimulated channel activity, which was abolished by inhibitors of IFN-␥ receptor-associated Janus-activated kinase [P6 (1 M) and AG490 (10 M)]. However, L-NAME did not block the acute effect of IFN-␥. Indeed, IFN-␥ did not acutely affect NO production. Moreover, the acute effect was not blocked by inhibition of PKA, PKG, and phosphatidylinositol 3-kinase (PI3K). We conclude that IFN-␥ exerted a delayed suppressive effect on K ϩ channel activity by enhancing iNOS expression and an acute stimulatory effect, which was independent of either NO pathways or phosphorylation processes mediated by PKA, PKG, and PI3K in RPTECs.

show abstract

“…P2Y 2 receptor Ϫ/Ϫ mice have been described previously (30). Likewise, isolation of collecting ducts suitable for electrophysiology has been described (29,31,32). In brief, mice were sacrificed by cervical dislocation and the kidneys immediately removed.…”

Section: Methodsmentioning

confidence: 99%

Paracrine Regulation of the Epithelial Na+ Channel in the Mammalian Collecting Duct by Purinergic P2Y2 Receptor Tone

Pochynyuk

Bugaj

Rieg

et al. 2008

Journal of Biological Chemistry

121

166

View full text Add to dashboard Cite

Growing evidence implicates a key role for extracellular nucleotides in cellular regulation, including of ion channels and renal function, but the mechanisms for such actions are inadequately defined. We investigated purinergic regulation of the epithelial Na ؉ channel (ENaC) in mammalian collecting duct. We find that ATP decreases ENaC activity in both mouse and rat collecting duct principal cells. ATP and other nucleotides, including UTP, decrease ENaC activity via apical P2Y 2 receptors. ENaC in collecting ducts isolated from mice lacking this receptor have blunted responses to ATP. P2Y 2 couples to ENaC via PLC; direct activation of PLC mimics ATP action. Tonic regulation of ENaC in the collecting duct occurs via locally released ATP; scavenging endogenous ATP and inhibiting P2 receptors, in the absence of other stimuli, rapidly increases ENaC activity. Moreover, ENaC has greater resting activity in collecting ducts from P2Y 2 ؊/؊ mice. Loss of collecting duct P2Y 2 receptors in the knock-out mouse is the primary defect leading to increased ENaC activity based on the ability of direct PLC stimulation to decrease ENaC activity in collecting ducts from P2Y 2 ؊/؊ mice in a manner similar to ATP in collecting ducts from wild-type mice. These findings demonstrate that locally released ATP acts in an autocrine/paracrine manner to tonically regulate ENaC in mammalian collecting duct. Loss of this intrinsic regulation leads to ENaC hyperactivity and contributes to hypertension that occurs in P2Y 2 receptor ؊/؊ mice. P2Y 2 receptor activation by nucleotides thus provides physiologically important regulation of ENaC and electrolyte handling in mammalian kidney. Systemic Naϩ balance influences blood pressure. Consequently, body Na ϩ content is under tight negative-feedback control by the renin-angiotensin-aldosterone system. Discretionary Na ϩ reabsorption in the aldosterone-sensitive distal renal nephron, including the collecting duct, fine-tunes plasma Na ϩ levels. Here, the activity of the luminal epithelial Na ϩ channel (ENaC) 2 is limiting for Na ϩ transport (1-3). ENaC is an end-effector of the renin-angiotensin-aldosterone system with aldosterone increasing ENaC activity. The importance of ENaC and its proper regulation to control of blood pressure is highlighted by several diseases associated with gain and loss of ENaC function (3, 4). For instance, gain of ENaC function results in inappropriate Na ϩ conservation and hypertension (e.g. Liddle syndrome). Conversely, loss of ENaC function results in renal salt wasting associated with hypotension (e.g. pseudohypoaldosteronism type 1).Although extrinsic regulation of ENaC in the distal nephron by hormones originating outside the kidney is considered pivotal to blood pressure control, complementary regulation of ENaC by autocrine/paracrine factors originating from intrarenal sources is just now becoming appreciated. ATP has been identified as a candidate signaling molecule possibly mediating intrinsic control of distal nephron Na ϩ reabsorption (5-14). ATP and other...

show abstract

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

Cited by 11 publications

References 40 publications

Acute Regulation of the Epithelial Na+ Channel by Phosphatidylinositide 3-OH Kinase Signaling in Native Collecting Duct Principal Cells

Acute Regulation of the Epithelial Na+ Channel by Phosphatidylinositide 3-OH Kinase Signaling in Native Collecting Duct Principal Cells

Delayed and acute effects of interferon-γ on activity of an inwardly rectifying K⁺ channel in cultured human proximal tubule cells

Paracrine Regulation of the Epithelial Na+ Channel in the Mammalian Collecting Duct by Purinergic P2Y2 Receptor Tone

Contact Info

Product

Resources

About

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

Cited by 11 publications

References 40 publications

Acute Regulation of the Epithelial Na+ Channel by Phosphatidylinositide 3-OH Kinase Signaling in Native Collecting Duct Principal Cells

Acute Regulation of the Epithelial Na+ Channel by Phosphatidylinositide 3-OH Kinase Signaling in Native Collecting Duct Principal Cells

Delayed and acute effects of interferon-γ on activity of an inwardly rectifying K+ channel in cultured human proximal tubule cells

Paracrine Regulation of the Epithelial Na+ Channel in the Mammalian Collecting Duct by Purinergic P2Y2 Receptor Tone

Contact Info

Product

Resources

About

Delayed and acute effects of interferon-γ on activity of an inwardly rectifying K⁺ channel in cultured human proximal tubule cells