Block by extracellular divalent cations of Drosophila big brain channels expressed in Xenopus oocytes

Biophys J. 2004 Mar;86(3):1470-8. doi: 10.1016/S0006-3495(04)74215-0.


Drosophila Big Brain (BIB) is a transmembrane protein encoded by the neurogenic gene big brain (bib), which is important for early development of the fly nervous system. BIB expressed in Xenopus oocytes is a monovalent cation channel modulated by tyrosine kinase signaling. Results here demonstrate that the BIB conductance shows voltage- and dose-dependent block by extracellular divalent cations Ca(2+) and Ba(2+) but not by Mg(2+) in wild-type channels. Site-directed mutagenesis of negatively charged glutamate (Glu(274)) and aspartate (Asp(253)) residues had no effect on divalent cation block. However, mutation of a conserved glutamate at position 71 (Glu(71)) in the first transmembrane domain (M1) altered channel properties. Mutation of Glu(71) to Asp introduced a new sensitivity to block by extracellular Mg(2+); substitutions with asparagine or glutamine decreased whole-cell conductance; and substitution with lysine compromised plasma membrane expression. Block by divalent cations is important in other ion channels for voltage-dependent function, enhanced signal resolution, and feedback regulation. Our data show that the wild-type BIB conductance is attenuated by external Ca(2+), suggesting that endogenous divalent cation block might be relevant for enhancing signal resolution or voltage dependence for the native signaling process in neuronal cell fate determination.

Publication types

  • Comparative Study
  • Evaluation Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Barium / pharmacology*
  • Calcium / pharmacology*
  • Cations, Divalent / pharmacology
  • Cells, Cultured
  • Drosophila
  • Drosophila Proteins / drug effects
  • Drosophila Proteins / physiology*
  • Extracellular Fluid / metabolism
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology*
  • Ion Channels / drug effects
  • Ion Channels / physiology*
  • Magnesium / pharmacology*
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Membrane Proteins / drug effects
  • Membrane Proteins / physiology*
  • Mutagenesis, Site-Directed
  • Oocytes / drug effects
  • Oocytes / physiology*
  • Recombinant Proteins / antagonists & inhibitors
  • Recombinant Proteins / metabolism
  • Structure-Activity Relationship
  • Xenopus laevis


  • Cations, Divalent
  • Drosophila Proteins
  • Ion Channels
  • Membrane Proteins
  • Recombinant Proteins
  • bib protein, Drosophila
  • Barium
  • Magnesium
  • Calcium