Antagonists-resistant calcium currents in rat embryo motoneurons

Eur J Neurosci. 1998 May;10(5):1810-25. doi: 10.1046/j.1460-9568.1998.00178.x.

Abstract

Ca2+ channels diversity of cultured rat embryo motoneurons was investigated with whole-cell current recordings. In 5-20 mM Ba2+, the whole-cell currents were separated in low- (LVA) and high-voltage-activated (HVA) current. The LVA current was evident since the first day in culture, while the HVA component was small and increased with time. Recordings after 4 days revealed approximately 20% L-, approximately 45% N- and approximately 35% P- and R-type currents. P-type currents were revealed only in 40% of motoneurons, in which 20-200 nM omega-Aga-IVA caused 20% irreversible block of total current. The remaining 60% of cells were insensitive even to higher doses of the toxin (500 nM in 5 mM Ba2+), suggesting weak expression and heterogeneous distribution of P-type channels compensated by high densities of HVA Ca2+ channels resistant to all the antagonists (R-type). A significant residual current could also be resolved after prolonged applications of 5 microM omega-CTx-MVIIC, which allowed separation of N- and P-type currents by the distinct onset of toxin block. The antagonists-resistant current reveals biophysical characteristics typical of HVA channels, but distinct from the alphaE channel. The current activates around -20 mV in 20 mM Ba2+; inactivates slowly and independently of Ca2+; is blocked by low [Cd2+] and high [Ni2+]; and is larger with Ba2+ than Ca2+. The uncovered R-type calcium current can account for part of the presynaptic Ca2+ current controlling neurotransmitter release at the mammalian neuromuscular junction whose activity is resistant to DHP-and omega-CTx-GVIA, and displays anomalous sensitivity to omega-Aga-IVA and omega-CTx-MVIIC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Barium / pharmacology
  • Calcium Channel Blockers / pharmacology*
  • Cells, Cultured
  • Drug Resistance
  • Embryo, Mammalian / cytology
  • Embryo, Mammalian / drug effects*
  • Ion Channels / physiology
  • Motor Neurons / drug effects*
  • Patch-Clamp Techniques
  • Peptides / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Spider Venoms / pharmacology
  • omega-Agatoxin IVA
  • omega-Conotoxin GVIA

Substances

  • Calcium Channel Blockers
  • Ion Channels
  • Peptides
  • Spider Venoms
  • omega-Agatoxin IVA
  • Barium
  • omega-Conotoxin GVIA

Grant support