Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The epithelial sodium channel is found in apical membranes of a variety of native epithelial tissues, where it regulates sodium and fluid balance. In vivo, a number of hormones and other endogenous factors, including polyunsaturated fatty acids (PUFAs), regulate these channels. We tested the effects of essential n-3 and n-6 PUFAs on amiloride-sensitive sodium transport in A6 epithelial cells. Eicosapentaenoic acid [EPA; C20:5(n-3)] transiently stimulated amiloride-sensitive open-circuit current (I(Na)) from 4.0 +/- 0.3 to 7.7 +/- 0.3 microA/cm2 within 30 min (P < 0.001). No activation was seen in the presence of 10 microM amiloride. In cell-attached but not in cell-excised patches, EPA acutely increased the open probability of sodium channels from 0.45 +/- 0.08 to 0.63 +/- 0.10 (P = 0.02, paired t-test). n-6 PUFAs, including linoleic acid (C18:2), eicosatetraynoic acid (C20:4), and docosapentanoic acid (C22:5) had no effect, whereas n-3 docosahexanoic acid (C22:6) activated amiloride-sensitive I(Na) in a manner similar to EPA. Activation of I(Na) by EPA was prevented by H-89, a PKA inhibitor. Similarly, PKA activity was stimulated by EPA. Nonspecific stimulation of phosphodiesterase activity by CoCl2 completely prevented the effect of EPA on sodium transport. We conclude that n-3 PUFAs activate epithelial sodium channels downstream of cAMP in a cAMP-dependent pathway also involving PKA.
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PMID:Modulation of epithelial Na+ channel activity by long-chain n-3 fatty acids. 1519 29

Essential polyunsatured fatty acids have been shown to modulate enzymes, channels and transporters, to interact with lipid bilayers and to affect metabolic pathways. We have previously shown that eicosapentanoic acid (EPA, C20:5, n-3) activates epithelial sodium channels (ENaCs) in a cAMP-dependent manner involving stimulation of cAMP-dependent protein kinase (PKA). In the present study, we explored further the mechanism of EPA stimulation of ENaC in A6 cells. Fluorescence resonance energy transfer experiments confirmed activation of PKA by EPA. Consistent with our previous studies, EPA had no further stimulatory effect on amiloride-sensitive transepithelial current (INa) in the presence of CPT-cAMP. Thus, we investigated the effect of EPA on cellular pathways which produce cAMP. EPA did not stimulate adenylate cyclase activity or total cellular cAMP accumulation. However, membrane-bound phosphodiesterase activity was inhibited by EPA from 2.46 pmol/mg of protein/min to 1.3 pmol/mg of protein/min. To investigate the potential role of an A-kinase-anchoring protein (AKAP), we used HT31, an inhibitor of the binding between PKA and AKAPs as well as cerulenin, an inhibitor of myristoylation and palmitoylation. Both agents prevented the stimulatory effect of EPA and CPT-cAMP on INa and drastically decreased the amount of PKA in the apical membrane. Colocalization experiments in A6 cells cotransfected with fluorescently labeled ENaC beta subunit and PKA regulatory subunit confirmed the close proximity of the two proteins and the membrane anchorage of PKA. Last, in A6 cells transfected with a dead mutant of Sgk, an enzyme which up-regulates ENaCs, EPA did not stimulate Na+ current. Our results suggest that stimulation of ENaCs by EPA occurs via SGK in membrane-bound compartments containing an AKAP, activated PKA, and a phosphodiesterase.
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PMID:Epithelial Na+ channel stimulation by n-3 fatty acids requires proximity to a membrane-bound A-kinase-anchoring protein complexed with protein kinase A and phosphodiesterase. 1747 24