title: Protein kinase regulation of a cloned epithelial Na+ channel.
abstract: We examined the regulation of a cloned epithelial Na+ channel (alpha beta gamma-rENaC) by protein kinase A (PKA) and protein kinase C (PKC). Experiments were performed in Xenopus oocytes and in planar lipid bilayers. At a holding potential of -100 mV, amiloride-sensitive current averaged -1,279 +/- 111 nA (n = 7) in alpha beta gamma-rENaC-expressing oocytes. Currents in water-injected oocytes were essentially unresponsive to 10 microM amiloride. A 1-h stimulation of PKC with 100 nM of PMA inhibited whole-cell currents in Xenopus oocytes to 17.1 +/- 1.8, and 22.1 +/- 2.6% of control (n = 7), at holding potentials of -100 and +40 mV, respectively. Direct injection of purified PKC resulted in similar inhibition to that observed with PMA. Additionally, the inactive phorbol ester, phorbol-12-myristate-13-acetate, 4-O-methyl, was without effect on alpha beta gamma-rENaC currents. Pretreatment with the microtubule inhibitor colchicine (100 microM) did not modify the inhibitory effect of PMA; however, pretreatment with 20 microM cytochalasin B decreased the inhibitory action of PMA to < 20% of that previously observed. In vitro-synthesized alpha beta gamma-rENaC formed an amiloride-sensitive Na(+)-selective channel when incorporated into planar lipid bilayers. Addition of PKC, diacyl-glycerol, and Mg-ATP to the side opposite that which amiloride blocked, decreased the channel's open probability (Po) from 0.44 +/- 0.06 to 0.13 +/- 0.03 (n = 9). To study the effects of PKA on alpha beta gamma-rENaC expressed in Xenopus oocytes, cAMP levels were elevated with 10 microM forskolin and 1 mM isobutyl-methyl-xanthine. This cAMP-elevating cocktail did not cause any stimulation of alpha beta gamma-rENaC currents in either the inward or outward directions. This lack of activation was also observed in oocytes preinhibited with PMA and in oocytes pretreated with cytochalasin B and PMA. Neither alpha-rENaC nor alpha beta gamma-rENaC incorporated into planar lipid bilayers could be activated with PKA and Mg-ATP added to either side of the membrane, as Po remained at 0.63 +/- 0.06 (n = 7) and 0.45 +/- 0.05 (n = 9), respectively. We conclude that: alpha beta gamma-rENaC is inhibited by PKC, and that alpha beta gamma-rENaC is not activated by PKA.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham 35294, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Awayda
authors.forename: I I
authors.initials: II
authors.lastname: Ismailov
authors.forename: B K
authors.initials: BK
authors.lastname: Berdiev
authors.forename: C M
authors.initials: CM
authors.lastname: Fuller
authors.forename: D J
authors.initials: DJ
authors.lastname: Benos
mesh_terms: D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011494:Protein Kinases / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects*; D014981:Xenopus
chemical_list: D015222:Sodium Channels; D005576:Colforsin; D011494:Protein Kinases