Characterization of a P-type calcium current in a crayfish motoneuron and its selective modulation by impulse activity

J Neurophysiol. 1997 Jan;77(1):76-85. doi: 10.1152/jn.1997.77.1.76.


Previous studies have demonstrated that the voltage-dependent Ca2+ current recorded from the cell body of the crayfish abdominal motoneuron, F3, undergoes a long-term reduction as a result of increased impulse activity. The properties of the Ca2+ channels undergoing this long-term change were examined with the use of two-electrode voltage-clamp techniques. The Ca2+ current was activated at -50 to -40 mV and its amplitude was maximal at 0 mV (-135.0 +/- 25.8 nA, mean +/- SE, n = 14). The current-voltage relationship and the greater sensitivity of the Ca2+ channel to Cd2+ than Ni2+ indicated that Ca2+ influx occurs through high-voltage-activated (HVA) Ca2+ channels. Loose-patch recordings demonstrated that the Ca2+ current was generated by the membrane of the cell body. When Ba2+ was substituted for extracellular Ca2+, there was a 40% increase in the amplitude of the inward current and a negative shift of approximately 10 mV in the I-V relationship. Application of the P-type Ca2+ channel antagonist omega-agatoxin IVA (omega-AgTX IVA) produced a significant 33% (n = 6) reduction in the peak amplitude of the Ba2+ current, whereas neither the L-type Ca2+ channel antagonist nifedipine nor the N-type channel antagonist omega-conotoxin GVIA produced a reduction in the Ba2+ current. The voltage-dependent activation of this P-type (omega-AgTX-IVA-sensitive) Ca2+ channel was similar to previously identified P-type channels, but different from that of the non-P-type (omega-AgTX-IVA-resistant) Ca2+ channels. When Ca2+ currents were measured 6-7 h after an increase in impulse activity (5-Hz stimulation for 45-60 min), there was a 43% reduction in the amplitude of the P-type current, but no significant changes in the non-P-type current amplitude. These results demonstrate that at least two subtypes of HVA Ca2+ channels contribute to the macroscopic Ca2+ current observed in the cell body of this crayfish phasic motoneuron: one belongs to the previously described P-type Ca2+ channel and the other(s) does not belong to the N-, L-, or P-type Ca2+ channel. The long-term, Ca(2+)-dependent reduction in Ca2+ current previously demonstrated in motoneuron F3 is produced by the selective reduction of this P-type Ca2+ current. This activity-dependent reduction in the P-type Ca2+ current is likely involved in the long-term depression of transmitter release observed at the neuromuscular synapses of this motoneuron.

Publication types

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

MeSH terms

  • Animals
  • Astacoidea / physiology*
  • Barium / metabolism
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / drug effects
  • Calcium Channels / physiology*
  • Electrophysiology
  • In Vitro Techniques
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Motor Neurons / drug effects
  • Motor Neurons / physiology*
  • Patch-Clamp Techniques
  • Scorpion Venoms / pharmacology
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*


  • Calcium Channel Blockers
  • Calcium Channels
  • Scorpion Venoms
  • agitoxin 2
  • Barium