Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Using patch clamp techniques, we found that the epithelial sodium channel (ENaC) activity in the apical membrane of A6 distal nephron cells showed a sudden rundown beginning at 4 min after forming the inside-out configuration. This sudden rundown was prevented by addition of anionic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP(2)), phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), and phosphatidylserine (PS) to the "cytoplasmic" bath. Conversely, chelation of endogenous PIP(2) with anti-PIP(2) antibody, hydrolysis of PIP(2) with either exogenous phospholipase C (PLC) or activation of endogenous PLC by extracellular ATP, or application of the positively charged molecule, poly-L-lysine, accelerated channel rundown. However, neutral phosphatidylcholine had no effect on ENaC activity. By two-electrode voltage clamp recordings, we demonstrated that PIP(2) and PIP(3) significantly increased amiloride-sensitive current in Xenopus oocytes injected with cRNAs of rat alpha-, beta-, and gamma-ENaC. However, PIP(2) and PIP(3) did not affect surface expression of ENaC, indicating that PIP(2) and PIP(3) regulate ENaC at the level of the inner plasma membrane through a mechanism that is independent of ENaC trafficking. These data suggest that anionic phospholipids may mediate the regulation of ENaC by PLC- or phosphoinositide 3-kinase-coupled receptors.
...
PMID:Anionic phospholipids regulate native and expressed epithelial sodium channel (ENaC). 1180 44

The mechanosensitivity of the epithelial sodium channel (ENaC) is controversial. Using cell-attached patch-clamp techniques, we found that mechanical stretch stimulated ENaC in A6 distal nephron cells in only three of nine cell-attached patches. However, stretch consistently activated ENaC after apical ATP was scavenged with apical hexokinase plus glucose or after P(2) receptors in the patch were blocked. The mean open probability (P(o)) of ENaC was increased from 0.31 +/- 0.04 to 0.61 +/- 0.06 (P < 0.001; n = 9) when patch pipettes contained hexokinase and glucose, or from 0.24 +/- 0.05 to 0.55 +/- 0.11 (P < 0.01; n = 7) when patch pipettes contained suramin, respectively. A poorly hydrolyzable ATP analog, ATPgammaS, in the patch pipettes inhibited ENaC, reducing the P(o) from 0.41 +/- 0.06 to 0.19 +/- 0.05 (P < 0.01; n = 8). Pretreatment of A6 cells with the phospholipase C (PLC) inhibitor U-73122 abolished the effect of ATP on ENaC activity. These data together suggest that ATP, acting through a PLC-dependent purinergic pathway, masks stretch-induced ENaC activation.
...
PMID:ATP masks stretch activation of epithelial sodium channels in A6 distal nephron cells. 1183 32

Phytohemagglutinins are widely distributed in common food items. They constitute a heterogeneous group of proteins, which are often resistant to proteolysis in the gastrointestinal tract. Upon binding to the luminal membrane of intestinal cells, they can interfere with digestive, protective or secretory functions of the intestine. Phytohemagglutinins present in red kidney beans and jackbeans have been shown to induce diarrhea and hypersecretion in human airways, but the underlying mechanisms remain obscure. We examined how agglutinins from wheat germ (WGA), soy bean (SBA), red kidney beans (Pha-E, Pha-L), and jackbeans (Con-A) affect ion transport in mouse airways and large intestine using Ussing chamber techniques. We found that Pha-E, Pha-L, and Con-A but not WGA and SBA inhibit electrogenic Na(+) absorption dose dependently in both colon and trachea. The inhibitory effects of Con-A on Na(+) absorption were suppressed by the sugar mannose, by inhibition of phospholipase C (PLC) and protein kinase C (PKC). Thus, nutritional phytohemagglutinins block salt absorption in a PLC- and PKC-dependent manner, probably by inhibition of the epithelial Na(+) channel (ENaC). This effect may be therapeutically useful in patients suffering from cystic fibrosis.
...
PMID:Effects of dietary lectins on ion transport in epithelia. 1523 2

Cystic fibrosis (CF) transmembrane conductance regulator (CFTR) Cl(-) channel function is required for activating amiloride-sensitive epithelial Na(+) channels (ENaC) in salt-absorbing human sweat duct. It is unclear whether ENaC channel function is also required for CFTR activation. The dysfunctional ENaC mutations in type-1 pseudohypoaldosteronism (PHA-1) provided a good opportunity to study this phenomenon of ion channel interaction between CFTR and ENaC. The PHA-1 ducts completely lacked spontaneous ENaC conductance (gENaC). In contrast, the normal ducts showed large spontaneous gENaC (46 +/- 10 ms, mean +/- SE: ). After permeabilization of the basolateral membrane with alpha-toxin, cAMP + ATP activation of CFTR Cl(-) conductance (gCFTR) or alkalinization of cytosolic pH (6.8 to 8.5) stimulated gENaC of normal but not PHA-1 ducts. In contrast, both spontaneous gCFTR in intact ducts and (cAMP + ATP)-activated gCFTR of permeabilized ducts appeared to be similar in normal and PHA-1 subjects. Lack of gENaC completely blocked salt absorption and caused dramatic reversal of skin potentials associated with pilocarpine-induced sweat secretion from significantly negative in normal subjects (-13 +/- 7.0 mV) to significantly positive (+22 +/- 11.0 mV) in PHA-1 patients. We conclude that virtual lack of ENaC in PHA-1 ducts had little effect on CFTR activity and that the positive skin potentials could potentially serve as a diagnostic tool to identify type-1 pseudohypoaldosteronism.
...
PMID:Normal CFTR Activity and Reversed Skin Potentials in Pseudohypoaldosteronism. 1598 94

The cystic fibrosis transmembrane conductance regulator (CFTR) is a protein kinase A and ATP-regulated Cl- channel that also controls the activity of other membrane transport proteins, such as the epithelial Na+ channel ENaC. Previous studies demonstrated that cytosolic domains of ENaC are critical for down-regulation of ENaC by CFTR, whereas others suggested a role of cytosolic Cl- ions. We therefore examined in detail the anion dependence of ENaC and the role of its cytosolic domains for the inhibition by CFTR and the Cl- channel CLC-0. Coexpression of rat ENaC with human CFTR or the human Cl- channel CLC-0 caused inhibition of amiloride-sensitive Na+ currents after cAMP-dependent stimulation and in the presence of a 100 mM bath Cl- concentration. After activation of CFTR by 3-isobutyl-1-methylxanthine and forskolin or expression of CLC-0, the intracellular Cl- concentration was increased in Xenopus oocytes in the presence of a high bath Cl- concentration, which inhibited ENaC without changing surface expression of alpha beta gammaENaC. In contrast, a 5 mM bath Cl- concentration reduced the cytosolic Cl- concentration and enhanced ENaC activity. ENaC was also inhibited by injection of Cl- into oocytes and in inside/out macropatches by exposure to high cytosolic Cl- concentrations. The effect of Cl- was mimicked by Br-, Br-, NO3(-), and I-. Inhibition by Cl- was reduced in trimeric channels with a truncated COOH terminus of betaENaC and gammaENaC, and it was no longer detected in dimeric alpha deltaCbeta ENaC channels. Deletion of the NH2 terminus of alpha-, beta-, or gammaENaC, mutations in the NH2-terminal phosphatidylinositol bisphosphate-binding domain of betaENaC and gammaEnaC, and activation of phospholipase C, all reduced ENaC activity but allowed for Cl(-)-dependent inhibition of the remaining ENaC current. The results confirm a role of the carboxyl terminus of betaENaC for Cl(-)-dependent inhibition of the Na+ channel, which, however, may only be part of a complex regulation of ENaC by CFTR.
...
PMID:Cl- interference with the epithelial Na+ channel ENaC. 1602 56

Regulation of cystic fibrosis transmembrane regulator (CFTR) and epithelial sodium channel (ENaC) in airway epithelia strongly influences the rate of mucociliary clearance (MCC) by determining the volume of airway surface liquid. MCC increases in response to stimuli originating on the airway surface, and CFTR and ENaC in airway epithelia appear to be regulated by local rather than systemic signaling. Although all signals that regulate CFTR and ENaC in airways have not been identified, the release of nucleotides from airway epithelial cells exposed to physical stimuli initiates a series of events that coordinately favor increased MCC. These events include activation of adenosine A2B receptors that stimulate CFTR and P2Y2 receptors that inhibit ENaC. Together these actions result in an increased volume of airway surface liquid and increased MCC rates. Stimulation of CFTR by A(2B)AR uses protein kinase (PK) A signaling elements that are localized within the apical/subapical compartment, including G proteins, adenylyl cyclase, PKA-II, A-kinase anchoring proteins, and phosphodiesterases. Inhibition of ENaC by P2Y2 receptors appears to be mediated by phospholipase C-beta3, possibly through an effect on the levels of phosphatidylinositol 4,5-bisphosphonate in the apical membrane.
...
PMID:Local regulation of cystic fibrosis transmembrane regulator and epithelial sodium channel in airway epithelium. 1611 9

Anionic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP(2)) and phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) are normally located in the inner leaflet of the plasma membrane, where these anionic phospholipids can regulate transmembrane proteins, including ion channels and transporters. Recent work has demonstrated that (1) ATP inhibits the renal epithelial sodium channel (ENaC) via a phospholipase C-dependent pathway that reduces PIP(2), (2) aldosterone stimulates ENaC via phosphoinositide 3-kinase, and (3) PIP(2) and PIP(3) regulate ENaC. Several lines of evidence show that ATP stimulation of purinergic P2Y receptors hydrolyzes PIP(2) and that aldosterone stimulation of steroid receptors induces PIP(3) formation. These studies together suggest that one primary mechanism for regulating ENaC is by alteration of anionic phospholipids and that the receptor-mediated and hormonal regulation of ENaC works through a variety of signaling pathways, but many of these pathways finally alter ENaC activity by regulating the formation or degradation of anionic phospholipids. Therefore, changes in the concentration of PIP(2) and PIP(3) are hypothesized to participate in the regulation of ENaC by purinergic and corticoid receptors. The underlying mechanism may be associated with a physical interaction of the positively charged cytoplasmic domains of the beta- and gamma-ENaC with the negatively charged membrane phospholipids. The exact nature of this interaction will require further investigation.
...
PMID:Acute regulation of epithelial sodium channel by anionic phospholipids. 1619 20

Recent reports have shown that cytokines inhibit fluid absorption by suppressing Na(+) channel activity in various epithelia. In this study, we investigated the role of epithelial sodium channel (ENaC) in fluid absorption in normal human middle ear epithelial (NHMEE) cells, as well as the effects of Interleukin (IL)-1beta on ENaC expression and fluid absorption in NHMEE cells. We confirmed that ENaC alpha, beta and gamma were predominantly expressed on the apical surface of the NHMEE cells by immunocytochemistry. Addition of amiloride, a potent ENaC blocker, to apical membranes of NHMEE cells decreased the fluid absorption rate in a dose-dependent manner. Treatment with 10 ng/ml IL-1beta for 24 h suppressed ENaC beta expression, the ENaC-dependent short-circuit current (Isc), and ENaC-dependent fluid absorption. When the NHMEE cells were pretreated with a phospholipase C (PLC)inhibitor (U73122, 10 microM), a protein kinase C (PKC) inhibitor (Calphostin C, 0.1 microM), or extracellular signal regulated kinase (ERK) 1/2 inhibitor (PD98059, 10 microM), the amiloride-sensitive currents in IL-1beta-treated cells were reversed to control levels; an effect not seen with SB202190 (an inhibitor of p38 mitogen-activated protein (MAP) kinase) or SP600125 (a reversible inhibitor of c-Jun N-terminal kinase). In this study we showed that ENaC is essential for fluid absorption in NHMEE cells and that IL-1beta suppresses the ENaC-dependent current via the PLC-PKC-ERK1/2 pathway. These results suggest that IL-1beta may contribute to fluid retention in otitis media with effusion by changing electrolyte transport and reducing middle ear epithelial fluid absorption.
...
PMID:Interleukin-1beta suppresses epithelial sodium channel beta-subunit expression and ENaC-dependent fluid absorption in human middle ear epithelial cells. 1749 39

Recent studies suggest that the activity of epithelial sodium channels (ENaC) is increased by phosphatidylinositides, especially phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P(3)). Stimulation of phospholipase C by either adenosine triphosphate (ATP)-activation of purinergic P2Y receptors or epidermal growth factor (EGF)-activation of EGF receptors reduces membrane PI(4,5)P(2), and consequently decreases ENaC activity. Since ATP and EGF may be trapped in cysts formed by the distal tubule, it is possible that ENaC inhibition induced by ATP and EGF facilitates cyst formation in polycystic kidney diseases (PKD). However, some results suggest that ENaC activity is increased in PKD. In contrast to P2Y and EGF receptors, stimulation of insulin-like growth factor-1 (IGF-1) receptor by aldosterone or insulin produces PI(3,4,5)P(3), and consequently increases ENaC activity. The acute effect of aldosterone on ENaC activity through PI(3,4,5)P(3) possibly accounts for the initial feedback for blood volume recovery after hypovolemic hypotension. PI(4,5)P(2) and PI(3,4,5)P(3), respectively, interacts with the N terminus of beta-ENaC and the C terminus of gamma-ENaC. However, whether ENaC selectively binds to PI(4,5)P(2) and PI(3,4,5)P(3) over other anionic phospholipids remains unclear.
...
PMID:Regulation of the epithelial sodium channel by phosphatidylinositides: experiments, implications, and speculations. 1760 40

We tested the hypothesis that the serine protease trypsin can indirectly activate the epithelial Na(+) channel (ENaC). Experiments were carried out in Xenopus oocytes and examined the effects on the channel formed by all three human ENaC subunits and that formed by Xenopus epsilon and human beta and gamma subunits (epsilonbetagammaENaC). Low levels of trypsin (1-10 ng/ml) were without effects on the oocyte endogenous conductances and were specifically used to test the effects on ENaC. Addition of 1 ng/ml trypsin for 60 min stimulated the amiloride-sensitive human ENaC conductance (g(Na)) by approximately 6-fold. This effect on the g(Na) was [Na(+)]-independent, thereby ruling out an interaction with channel feedback inhibition by Na(+). The indirect nature of this activation was confirmed in cell-attached patch clamp experiments with trypsin added to the outside of the pipette. Trypsin was comparatively ineffective at activating epsilonbetagammaENaC, a channel that exhibited a high spontaneous open probability. These observations, in combination with surface binding experiments, indicated that trypsin indirectly activated membrane-resident channels. Activation by trypsin was also dependent on catalytic activity of this protease but was not accompanied by channel subunit proteolysis. Channel activation was dependent on downstream activation of G-proteins and was blocked by G-protein inhibition by injection of guanyl-5'-yl thiophosphate and by pre-stimulation of phospholipase C. These data indicate a receptor-mediated activation of ENaC by trypsin. This trypsin-activated receptor is distinct from that of protease-activated receptor-2, because the response to trypsin was unaffected by protease-activated receptor-2 overexpression or knockdown.
...
PMID:Indirect activation of the epithelial Na+ channel by trypsin. 1762 47


1 2 3 Next >>

---