Molecular Determinants of Ca2+ Selectivity and Ion Permeation in L-type Ca2+ Channels

Nature. 1993 Nov 11;366(6451):158-61. doi: 10.1038/366158a0.

Abstract

Voltage-gated Ca2+ channels link changes in membrane potential to the delivery of Ca2+, a key second messenger for many cellular responses. Ca2+ channels show selectivity for Ca2+ over more plentiful ions such as Na+ or K+ by virtue of their high-affinity binding of Ca2+ within the pore. It has been suggested that this binding involves four conserved glutamate residues in equivalent positions in the putative pore-lining regions of repeats I-IV in the Ca2+ channel a1 subunit. We have carried out a systematic series of single amino-acid substitutions in each of these positions and find that all four glutamates participate in high-affinity binding of Ca2+ or Cd2+. Each glutamate carboxylate makes a distinct contribution to ion binding, with the carboxylate in repeat III having the strongest effect. Some single glutamate-to-lysine mutations completely abolish micromolar Ca2+ block, indicating that the pore does not possess any high-affinity binding site that acts independently of the four glutamate residues. The prevailing model of Ca2+ permeation must thus be modified to allow binding of two Ca2+ ions in close proximity, within the sphere of influence of the four glutamates. The functional inequality of the glutamates may be advantageous in allowing simultaneous interactions with multiple Ca2+ ions moving single-file within the pore. Competition among Ca2+ ions for individual glutamates, together with repulsive ion-ion electrostatic interaction, may help achieve rapid flux rates through the channel.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calcium / metabolism*
  • Calcium Channels / classification
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Cell Membrane Permeability
  • Cells, Cultured
  • Glutamates / metabolism
  • Ions
  • Molecular Sequence Data
  • Mutation
  • Myocardium / metabolism
  • Rabbits
  • Xenopus

Substances

  • Calcium Channels
  • Glutamates
  • Ions
  • Calcium