Spatial calcium buffering in saccular hair cells

Nature. 1993 May 6;363(6424):74-6. doi: 10.1038/363074a0.


The potential importance of intracellular calcium-binding proteins in rapid and highly localized Ca2+ signalling is poorly understood. During fast synaptic transmission, which occurs at specialized active zones where Ca2+ diffuses only a few tens of nanometers from channels to neurotransmitter release sites, a cytoplasmic Ca2+ buffer would have to be extremely fast or present in millimolar concentrations to intercept a significant fraction of the calcium ions en route to their targets. Therefore, Ca2+ buffers have been presumed to be unimportant in fast exocytosis and another fast calcium-mediated process, electrical resonance in hair cells. Here I present evidence to the contrary by showing that hair cells in the frog sacculus contain millimolar concentrations of a mobile cytoplasmic calcium buffer that captures Ca2+ within a few microseconds after it enters through presynaptic Ca2+ channels and carries it away from the point of entry. This spatial buffering reduces the presynaptic free Ca2+ by up to 60 per cent and probably restricts the region in which the internal calcium ion concentration exceeds 1 microM to within < 250 nm of each synaptic site. The buffer can thus influence both electrical resonance and synaptic transmission. Calbindin-D28K or a related protein may serve as the mobile calcium buffer, an action similar to its function in transporting Ca2+ across intestinal epithelial cells.

Publication types

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

MeSH terms

  • Animals
  • Buffers
  • Calcium / metabolism*
  • Calcium-Binding Proteins / metabolism*
  • Hair Cells, Auditory / metabolism*
  • Membrane Potentials
  • Rana pipiens
  • Saccule and Utricle / metabolism*
  • Synaptic Membranes / metabolism*


  • Buffers
  • Calcium-Binding Proteins
  • Calcium