Ionic current of an identifiable giant neurone, d-RPLN, of an African giant snail (Achatina fulica Férussac), measured under voltage clamping--II. Outward currents.

1. The outward currents of d-RPLN (dorsal-right parietal large neurone), one of the largest identifiable neurones of an African giant snail, were studied. 2. At the holding potential (-90 mV) and at the command voltage (Vc20 mV), the current values were 3.05 +/- 0.13 microA (M +/- SE) for the peak (n = 38), and 1.96 +/- 0.10 microA for the plateau (n = 37). 3. The peak time constant (Vc = 0 mV) was 2.05 +/- 0.08 msec. 4. Tetraethylammonium at 50 mM reduced the plateau value up to 50-55% of the normal, but had little effect on the peak. 5. 5-Aminopyridine at 5.0 mM diminished the peak value to about 50-55%, and delayed the peak time. 6. Quinine at 0.25 mM decreased both the peak and the plateau approximately to 55-65% of their controls, but shortened the peak time when Vc was beyond 0 mV, in contrast to the case of 4-AP. 7. The calcium-free state (replaced with cobalt) reduced these currents to about 75% of the normal, and evidently delayed the peak time.