The action potential (AP) of the giant neuron of the molluskPlanorbis corneus exhibits an increased sensitivity of the spike overshoot to external sodium concentration in solutions containing a significantly lowered concentration of calcium. These results suggest that during the AP both sodium and calcium ions may act as carriers of the inward-directed current. During repeated responses the role of calcium ions in AP generation increases while that of sodium decreases. A delay in repolarization can occasionally be observed at the beginning of the falling phase of the AP. This delay is considered to be a result of a decrease in efficiency of the repolarizing action of the outward potassium current due to competition from a current entering the cell at the time of the falling phase. Results suggest that the carrier of this inward current is calcium.
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Magura, I.S. Action potentials of the mollusk giant neuron with changes in extracellular concentrations of sodium and calcium ions. Neurophysiology 1, 85–91 (1969). https://doi.org/10.1007/BF01064547
- Generation Increase
- Sodium Concentration
- Potassium Current