Separation of calcium channel current components in mouse chromaffin cells superfused with low- and high-barium solutions

Pflugers Arch. 1998 Jun;436(1):75-82. doi: 10.1007/s004240050606.


This study was carried out to characterize the set of voltage-dependent Ca2+ channel subtypes expressed by mouse adrenal chromaffin cells superfused with solutions containing low (2 mM) or high (10 mM) Ba2+ concentrations. Using 50-ms test pulses at 0 mV from a holding potential of -80 mV, averaged peak current in 10 mM Ba2+ was around 1 nA, and in 2 mM Ba2+ 0.36 nA. When using 2 mM Ba2+ as the charge carrier, nifedipine (3 microM) blocked IBa by 40-45%. omega-Conotoxin GVIA (1 microM) caused 26% inhibition, while omega-conotoxin MVIIC (3 microM) produced a 48% blockade. At low concentrations (20 nM), omega-agatoxin IVA caused 5-15% of current inhibition, while 2 microM gave rise to a 35-40% blockade. In 10 mM Ba2+, the blocking effects of nifedipine (40%) and omega-conotoxin GVIA (25%) were similar to those seen in 2 mM Ba2+. In contrast, blockade by omega-conotoxin MVIIC was markedly reduced in 10 mM Ba2+ (20-25%) as compared to 10 mM Ba2+ (48%). The blocking actions of omega-agatoxin IVA (2 microM) were also slowed down in 10 mM Ba2+, though the final blockade was unaffected. In 2 mM Ba2+, IBa was quickly inhibited by over 94% with combined nifedipine + omega-conotoxin MVIIC + omega-conotoxin GVIA; in 10 mM Ba2+, IBa was blocked by 70% with this combination. The data suggest that mouse chromaffin cells express L-type (40%) as well as non-L-type (60%) high-threshold voltage-dependent Ca2+ channels. The current carried by non-L-type Ca2+ channels consists of about 25% N-type and 35% P/Q-type; P-type channels, if anything, are poorly expressed. The data also indicate that the fraction of current blocked by omega-conotoxin MVIIC and omega-agatoxin IVA might considerably change as a function of the Ba2+ concentration of the extracellular solution; taking this fact into consideration, it seems that a residual R-type current is not expressed in mouse chromaffin cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenal Glands / drug effects
  • Adrenal Glands / physiology*
  • Animals
  • Barium / administration & dosage
  • Barium / pharmacology*
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / classification*
  • Calcium Channels / physiology*
  • Cations, Divalent
  • Cells, Cultured
  • Chromaffin System / drug effects
  • Chromaffin System / physiology*
  • Electric Conductivity
  • Mice
  • Nifedipine / pharmacology
  • Patch-Clamp Techniques
  • Peptides / pharmacology
  • Perfusion
  • Solutions
  • Spider Venoms / pharmacology
  • omega-Agatoxin IVA
  • omega-Conotoxin GVIA
  • omega-Conotoxins*


  • Calcium Channel Blockers
  • Calcium Channels
  • Cations, Divalent
  • Peptides
  • Solutions
  • Spider Venoms
  • omega-Agatoxin IVA
  • omega-Conotoxins
  • omega-conotoxin-MVIIC
  • Barium
  • omega-Conotoxin GVIA
  • Nifedipine