title: Regulation of epithelial sodium channels by short actin filaments.
abstract: Cytoskeletal elements play an important role in the regulation of ion transport in epithelia. We have studied the effects of actin filaments of different length on the alpha, beta, gamma-rENaC (rat epithelial Na+ channel) in planar lipid bilayers. We found the following. 1) Short actin filaments caused a 2-fold decrease in unitary conductance and a 2-fold increase in open probability (Po) of alpha,beta,gamma-rENaC. 2) alpha,beta,gamma-rENaC could be transiently activated by protein kinase A (PKA) plus ATP in the presence, but not in the absence, of actin. 3) ATP in the presence of actin was also able to induce a transitory activation of alpha, beta,gamma-rENaC, although with a shortened time course and with a lower magnitude of change in Po. 4) DNase I, an agent known to prohibit elongation of actin filaments, prevented activation of alpha,beta,gamma-rENaC by ATP or PKA plus ATP. 5) Cytochalasin D, added after rundown of alpha,beta,gamma-rENaC activity following ATP or PKA plus ATP treatment, produced a second transient activation of alpha,beta,gamma-rENaC. 6) Gelsolin, a protein that stabilizes polymerization of actin filaments at certain lengths, evoked a sustained activation of alpha,beta,gamma-rENaC at actin/gelsolin ratios of <32:1, with a maximal effect at an actin/gelsolin ratio of 2:1. These results suggest that short actin filaments activate alpha, beta,gamma-rENaC. PKA-mediated phosphorylation augments activation of this channel by decreasing the rate of elongation of actin filaments. These results are consistent with the hypothesis that cloned alpha,beta,gamma-rENaCs form a core conduction unit of epithelial Na+ channels and that interaction of these channels with other associated proteins, such as short actin filaments, confers regulation to channel activity.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Berdiev
authors.forename: A G
authors.initials: AG
authors.lastname: Prat
authors.forename: H F
authors.initials: HF
authors.lastname: Cantiello
authors.forename: D A
authors.initials: DA
authors.lastname: Ausiello
authors.forename: C M
authors.initials: CM
authors.lastname: Fuller
authors.forename: B
authors.initials: B
authors.lastname: Jovov
authors.forename: D J
authors.initials: DJ
authors.lastname: Benos
authors.forename: I I
authors.initials: II
authors.lastname: Ismailov
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D015640:Ion Channel Gating; D008051:Lipid Bilayers / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D008051:Lipid Bilayers; D011994:Recombinant Proteins; D015222:Sodium Channels; D000255:Adenosine Triphosphate