The calcium component of the action potential in spinal motoneurones of the rat.

Intracellular recordings were made from motoneurones of the neonatal rat (1‐14 days old) spinal cord isolated and perfused in vitro. An increase in extracellular Ca2+ concentration from 2 to 20 mM produced an increase in the amplitude of the after‐depolarization (a.d.p.), while replacement of Ca2+ by Mn2+ virtually abolished the a.d.p. These changes in the a.d.p. occurred in parallel with those in the after‐hyperpolarization (a.h.p.). The amplitudes of the a.d.p. and the a.h.p. were dependent upon the membrane potential: hyperpolarization increased the a.d.p. and decreased the a.h.p.; the opposite effects were produced by depolarization. The presence of Ca2+ spikes was demonstrated either by suppression of the voltage‐dependent K+ conductance with tetraethylammonium (TEA) or after blocking the Na+ spike. The Ca2+ spike was all‐or‐none in nature and blocked by Mn2+ or Co2+. The a.h.p. amplitude was dependent upon the extracellular K+ concentration but also correlated with the amplitude of the Ca2+‐dependent response. It is concluded that the a.d.p. is a Ca2+‐dependent potential whose amplitude is under normal conditions markedly reduced by the voltage‐dependent K+ conductance; the a.h.p. seems to be produced by an increase in the Ca2+‐dependent K+ conductance.

[1]  B. Gustafsson,et al.  Afterhyperpolarization conductance time course in lumbar motoneurones of the cat. , 1974, Acta physiologica Scandinavica.

[2]  D. Kernell,et al.  Delayed depolarization and the repetitive response to intracellular stimulation of mammalian motoneurones , 1963, The Journal of physiology.

[3]  K. Krnjević,et al.  EGTA and motoneuronal after‐potentials. , 1978, Journal of Physiology.

[4]  B. Gustafsson.  Afterhyperpolarization and the control of repetitive firing in spinal neurones of the cat. , 1974, Acta physiologica Scandinavica. Supplementum.

[5]  R. Meech,et al.  Intracellular calcium injection causes increased potassium conductance in Aplysia nerve cells. , 1972, Comparative biochemistry and physiology. A, Comparative physiology.

[6]  J. Blankenship.  Action of tetrodotoxin on spinal motoneurons of the cat. , 1968, Journal of neurophysiology.

[7]  K. Krnjević,et al.  Effects of some divalent cations on motoneurones in cats. , 1979, Canadian journal of physiology and pharmacology.

[8]  R. Miledi,et al.  Electrical synapses between motoneurons in the spinal cord of the newborn rat , 1980, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[9]  B. Katz,et al.  Tetrodotoxin‐resistant electric activity in presynaptic terminals , 1969, The Journal of physiology.

[10]  D. Kernell.  THE DELAYED DEPOLARIZATION IN CAT AND RAT MOTONEURONES. , 1964, Progress in brain research.

[11]  S. Konishi,et al.  Electrophysiology of mammalian spinal cord in vitro , 1974, Nature.

[12]  Calcium Spike in the Mammalian Spinal Motoneuron , 1981 .

[13]  Patrick L. McGeer,et al.  Molecular Neurobiology of the Mammalian Brain , 1978, Springer US.

[14]  J. Eccles,et al.  The recording of potentials from motoneurones with an intracellular electrode , 1952, The Journal of physiology.

[15]  P. G. Nelson,et al.  Delayed depolarization in cat spinal motoneurons. , 1967, Experimental neurology.

[16]  J. Eccles,et al.  The electrical properties of the motoneurone membrane , 1955, The Journal of physiology.

[17]  R. Miledi,et al.  Voltage sensitive calcium entry in frog motoneurones. , 1980, The Journal of physiology.

[18]  K. Krnjević,et al.  Injections of calcium ions into spinal motoneurones , 1972, The Journal of physiology.

[19]  D. Kernell.  The Limits of Firing Frequency in Cat Lumbosacral Motoneurones Possessing Different Time Course of Afterhyperpolarization , 1965 .

[20]  E. Barrett,et al.  Separation of two voltage‐sensitive potassium currents, and demonstration of a tetrodotoxin‐resistant calcium current in frog motoneurones. , 1976, The Journal of physiology.