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Proteolytically cleaved ENaC modulates a vesicle recycling pool responsible for cAMP‐stimulated channel insertion
Author(s) -
Butterworth Michael Bruce,
Edinger Robert S.,
Peters Kathryn W.,
Johnson John P.,
Frizzell Raymond A.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a794-c
Subject(s) - epithelial sodium channel , microbiology and biotechnology , forskolin , sodium channel , chemistry , apical membrane , vesicle , epithelial polarity , stimulation , intracellular , medicine , endocrinology , biology , sodium , cell , biochemistry , membrane , organic chemistry
Epithelial sodium channel (ENaC) surface density in cells of the kidney distal nephron is established by regulated insertion to, and removal from, the apical membrane (channel number change). Many components involved in regulated removal and degradation of ENaC from the apical surface have been characterized, but less is known about ENaC delivery. We have shown previously that ENaC is inserted into the apical membrane from an intracellular vesicle pool. The role ENaC plays in establishing the size of this pool and regulation of the trafficked vesicles, is unclear. By reducing proteolytically cleaved (active) ENaC expression in a model mouse cortical collecting duct cell line, basal and cAMP‐stimulated sodium short‐circuit current (I Na ) response were significantly reduced (control forskolin stimulated I Na = 27.9 ±1.3μA/cm 2 vs. stimulated experimental I Na = 5.8 ±2.3 μA/cm 2 , n>4). Total levels of ENaC expression, as determined by Western blotting, remained unchanged Simultaneous capacitance measurements showed a significantly smaller response to cAMP compared to control (6.7± 1.3% vs.12.9 ±1.6% increase, n=5) suggesting reduced membrane trafficking to the apical surface. When the cellular pool of cleaved ENaC was enlarged by hormonal stimulation, cAMP current and capacitance responses returned to control values. Cleaved ENaC constituted the majority of channels trafficked in response to cAMP stimulation, suggesting a population of active channels may determine the size of the regulated trafficking compartment.