Abstract
1. The long-term effects of ouabain on the membrane potential of the Anisodoris giant neurone (G cell) were examined in cells maintained for periods of up to 15 hr at 11-13° C.
2. In the presence of ouabain (5 × 10-4 M), the membrane potential depolarized to a constant level for 1-4 hr, then hyperpolarized for 5-7 hr after which it gradually depolarized again.
3. During the hyperpolarizing phase, after 6-8 hr in ouabain, [K]1 fell approximately 50%, [Na]1 increased 50-100% and the PNa/PK ratio decreased to 25% of its initial value.
4. After 8 hr in ouabain the membrane conductance increased two- to fourfold. This increase was independent of temperature and membrane rectification.
5. The K permeability (PK) was calculated from the constant field equation, and showed a fourfold increase after long-term treatment with ouabain. This rise in PK probably underlies the membrane hyperpolarization and the decrease in the PNa/PK ratio.
6. It is suggested that inhibition of the Na+ pump with ouabain causes a gradual rise in [Na]1 which secondarily leads to Ca2+ uptake, an increase in [Ca]1, and thereby an increase in PK.
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