Post‐tetanic hyperpolarization and electrogenic Na pump in stretch receptor neurone of crayfish

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Abstract
1. Two types of after‐potentials in the stretch receptor neurone of crayfish are described. 2. A short‐duration after‐hyperpolarization associated with a single spike or a few spikes is diminished and reversed on applying hyperpolarizing currents. However, a much longer‐lasting post‐tetanic hyperpolarization (PTH) is enhanced by conditioning hyperpolarization; thus, no reversal potential can be obtained. 3. No changes in membrane conductance occur during PTH. 4. Reducing K concentration in the bathing fluid diminishes PTH, while it shifts the reversal potential of the short after‐potential toward greater negativity. 5. Replacement of Na with Li, or addition of 2,4‐dinitrophenol in the bathing fluid suppresses PTH in a reversible manner. 6. Electrophoretic injection of Na into the cell induces a long‐lasting hyperpolarization. 7. No change in K‐equilibrium potential, as indicated by the reversal point of the short after‐potential, is detected during PTH. 8. It is concluded that the short after‐potential is caused by a permeability increase for potassium ion, whereas PTH is produced by an electrogenic Na‐pump.