Endogenous and exogenous Ca2+ buffers differentially modulate Ca2+-dependent inactivation of Ca(v)2.1 Ca2+ channels

J Biol Chem. 2006 Feb 24;281(8):4691-8. doi: 10.1074/jbc.M511971200. Epub 2005 Dec 22.


Voltage-gated Ca2+ channels undergo a negative feedback regulation by Ca2+ ions, Ca2+-dependent inactivation, which is important for restricting Ca2+ signals in nerve and muscle. Although the molecular details underlying Ca2+-dependent inactivation have been characterized, little is known about how this process might be modulated in excitable cells. Based on previous findings that Ca2+-dependent inactivation of Ca(v)2.1 (P/Q-type) Ca2+ channels is suppressed by strong cytoplasmic Ca2+ buffering, we investigated how factors that regulate cellular Ca2+ levels affect inactivation of Ca(v)2.1 Ca2+ currents in transfected 293T cells. We found that inactivation of Ca(v)2.1 Ca2+ currents increased exponentially with current amplitude with low intracellular concentrations of the slow buffer EGTA (0.5 mm), but not with high concentrations of the fast Ca2+ buffer BAPTA (10 mm). However, when the concentration of BAPTA was reduced to 0.5 mm, inactivation of Ca2+ currents was significantly greater than with an equivalent concentration of EGTA, indicating the importance of buffer kinetics in modulating Ca2+-dependent inactivation of Ca(v)2.1. Cotransfection of Ca(v)2.1 with the EF-hand Ca2+-binding proteins, parvalbumin and calbindin, significantly altered the relationship between Ca2+ current amplitude and inactivation in ways that were unexpected from behavior as passive Ca2+ buffers. We conclude that Ca2+-dependent inactivation of Ca(v)2.1 depends on a subplasmalemmal Ca2+ microdomain that is affected by the amplitude of the Ca2+ current and differentially modulated by distinct Ca2+ buffers.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Blotting, Western
  • Buffers
  • Calbindins
  • Calcium / chemistry*
  • Calcium / metabolism
  • Calcium Channels, N-Type / chemistry*
  • Calcium Channels, N-Type / metabolism
  • Cell Line
  • Cytoplasm / metabolism
  • DNA, Complementary / metabolism
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / chemistry
  • Egtazic Acid / pharmacology
  • Electrophysiology
  • Gene Expression Regulation*
  • Humans
  • Kinetics
  • Models, Biological
  • Parvalbumins / chemistry
  • Patch-Clamp Techniques
  • Rats
  • S100 Calcium Binding Protein G / chemistry
  • Transfection


  • Buffers
  • Calbindins
  • Calcium Channels, N-Type
  • DNA, Complementary
  • Parvalbumins
  • S100 Calcium Binding Protein G
  • voltage-dependent calcium channel (P-Q type)
  • Egtazic Acid
  • 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
  • Calcium