Voltage, temperature and ionic dependence of the slow outward current in Aplysia burst-firing neurones.

1. The slow outward current in Aplysia burst-firing neurones was studied under voltage-clamp conditions. This current, designated Iso, was measured as the incremental outward tail current following small depolarizing commands. 2. Iso was shown to be a pure K+ current, probably activated by the influx of Ca2+ during the depolarizing command (Johnston, 1976). For small depolarizations, the peak conductance was about 10(-7) mhos. 3. The rate of decay of Iso could be fit by a single exponential and was voltage-dependent, increasing with depolarization. 4. The decay rate of Iso was also temperature-dependent, with a Q10 of about 3. The peak conductance, however, was much less temperature-sensitive, with a Q10 of about 1.5. 5. The voltage dependence of decay rate suggested either the presence of a voltage-dependent Ca2+ pump or that the change in intracellular calcium concentration was not the rate-limiting step in the decay of Iso.