title: Functional role of the carboxyl terminal domain of human connexin 50 in gap junctional channels.
abstract: Gap junction channels formed by connexin 50 (Cx50) are critical for maintenance of lens transparency. Because the C-terminus of Cx50 can be cleaved post-translationally, we hypothesized that channels formed by the truncated Cx50 exhibit altered properties or regulation. We used the dual whole-cell patch-clamp technique to investigate the macroscopic and single-channel properties of gap junctional channels formed by wild-type human Cx50 and a truncation mutant (Cx50A294stop) after transfection of N2A cells. Our results show that wild-type Cx50 formed functional gap junctional channels. The macroscopic Gjss-Vj relationship was well described by a Boltzmann equation with A of 0.10, V0 of 43.8 mV and Gjmin of 0.23. The single-channel conductance was 212 +/- 5 pS. Multiple long-lasting substates were observed with conductances ranging between 31 and 80 pS. Wild-type Cx50 gap junctional channels were reversibly blocked when pHi was reduced to 6.3. Truncating the C-terminus at amino acid 294 caused a loss of pHi sensitivity, but there were no significant changes in single-channel current amplitude or Gjss-Vj relationship. These results suggest that the C-terminus of human Cx50 is involved in pHi sensitivity, but has little influence over single-channel conductance, voltage dependence, or gating kinetics.
authors.affiliation: Department of Physiology and Biophysics, Finch University of Health Science/The Chicago Medical School, 3333 Green Bay Rd, North Chicago, IL 60064, USA.
authors.forename: X
authors.initials: X
authors.lastname: Xu
authors.forename: V M
authors.initials: VM
authors.lastname: Berthoud
authors.forename: E C
authors.initials: EC
authors.lastname: Beyer
authors.forename: L
authors.initials: L
authors.lastname: Ebihara
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017630:Connexins; D003593:Cytoplasm; D004553:Electric Conductivity; D004594:Electrophysiology; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology*; D017629:Gap Junctions / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012756:Sheep; D014407:Tumor Cells, Cultured; D000099264:Connexin 50
chemical_list: D017630:Connexins; D005136:Eye Proteins; D007473:Ion Channels; D000099264:Connexin 50