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1. The ionic requirements of the action potential recorded in the cell of an identified cockroach (Periplaneta americana) motoneurone following pre-treatment of the animal with colchicine have been studied. 2. Small cubes of gelatin containing 1% colchicine were implanted into one metathoracic leg near to the nerve trunk containing the axon of the identified motoneurone. 3. Electrophysiological experiments were performed 4--10 days after this treatment, when action potentials which frequently overshoot zero potential can be recorded from the cell body. Such action potentials are not normally seen in untreated animals. 4. Sodium-free solution reversibly abolished the action potential within 5 min. 5. Tetrodotoxin (10(-8)M) reversibly depressed the action potential. It was totally abolished by 10(-7)M tetrodotoxin, but this effect was not reversible. 6. Saline solution containing 40 mM manganous chloride either had no effect on the action potential amplitude, or caused a slight increase. It also caused prolongation of the falling phase and loss of the after-hyperpolarization. These effects were all reversible. 7. It is concluded that sodium carries a major proportion of the inward current of the action potential in this neurone. Some calcium probably enters also, and may, at least in part, be responsible for triggering the delayed rise in potassium conductance during the action potential.

This article has been cited by other articles:

				J. D. Mills and R. M. Pitman Contribution of Potassium Conductances to a Time-Dependent Transition in Electrical Properties of a Cockroach Motoneuron Soma J Neurophysiol, May 1, 1999; 81(5): 2253 - 2266. [Abstract] [Full Text] [PDF]

				H. Le Corronc, B. Hue, and R. M. Pitman Ionic Mechanisms Underlying Depolarizing Responses of an Identified Insect Motor Neuron to Short Periods of Hypoxia J Neurophysiol, January 1, 1999; 81(1): 307 - 318. [Abstract] [Full Text] [PDF]

				J. D. Mills and R. M. Pitman Electrical Properties of a Cockroach Motor Neuron Soma Depend on Different Characteristics of Individual Ca Components J Neurophysiol, November 1, 1997; 78(5): 2455 - 2466. [Abstract] [Full Text] [PDF]