Injections of calcium ions into spinal motoneurones

J Physiol. 1972 Sep;225(2):363-90. doi: 10.1113/jphysiol.1972.sp009945.


1. In cats under Dial anaesthesia, Ca(2+) was injected inside lumbosacral motoneurones, by passing currents between CaCl(2)- and KCl-containing barrels of compound micropipettes.2. There was a reduction in excitability and a fall in membrane resistance, both rapid in onset and quickly reversible.3. The minimum effective injection current was approximately 10 nA, and the effect reached a maximum with currents of approximately 30 nA. The mean slope of resistance change against injection current was -1.7%/nA (S.E. 0.35).4. The most common change in membrane potential was a hyperpolarization; but in nearly half the cases, there was no clear change or a small depolarization. A reversal level for the effect of Ca(2+) could be measured in five cells: on the average, it was 10 mV more negative than the resting potential.5. Observations on i.p.s.p.s showed that Ca(2+) probably does not alter g(Cl): it was concluded that the fall in membrane resistance caused by intracellular Ca(2+) is mainly due to an increase in g(K).6. These results confirm previous suggestions that a steep transmembrane gradient of Ca(2+) is essential for the maintenance of a low membrane conductivity, and that a rise in internal free Ca(2+) - whether due to influx or release from internal stores - may play an important role in regulating neuronal activity.

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Calcium / pharmacology*
  • Cats
  • Cell Membrane Permeability / drug effects
  • Chlorides / metabolism
  • Electric Conductivity / drug effects
  • Injections
  • Iontophoresis
  • Lumbosacral Region
  • Membrane Potentials / drug effects
  • Motor Neurons / drug effects*
  • Potassium / metabolism
  • Sodium / metabolism
  • Spinal Cord / cytology*


  • Chlorides
  • Sodium
  • Potassium
  • Calcium