Active Transport of Potassium by the Giant Neuron of the Aplysia Abdominal Ganglion

We measured the internal potassium activity, a(i) (K), and membrane potential, E(m), simultaneously in 111 R2 giant neurons of Aplysia californica. a(i) (K) was 165.3 ± 3.4 mM, E(m) was -47.8 ± 0.9 mv, and E (K) calculated using the Nernst equation was -76.9 ± 0.05 mv. Such values were maintained for as long as 6 hr of continuous recording in untreated cells, a(i) (K) fell exponentially after the following treatments: cooling to 0.5°–4°C, ouabain, zero external potassium, 2,4-dinitrophenol, and cyanide. The effects of cooling and zero potassium were reversible. Potassium permeability was calculated from net potassium flux using the constant field equation and ranged from 2.6 to 18.5 x 10(-8) cm/sec. We conclude that potassium is actively transported into this neuron against a 30–40 mv electrochemical gradient.