Properties of a Ca2+ activated K+ conductance in /Helix neurones investigated by intracellular Ca2+ ionophoresis

Abstract

1. Membrane current responses produced by intracellular ionophoretic injection of Ca²⁺ ions into voltage clampedHelix neurones were investigated. 2. The Ca²⁺ activated current depends on the intensity and duration of the Ca²⁺ injection as well as on the membrane potential. The current-voltage relation is nonlinear and shows strong outward rectification. 3. The Ca²⁺ activated current reverses near the equilibrium potential for K⁺ ions and the associated current fluctuations disappear at the K⁺ reversal potential, which indicates a single current source, probably activation of K⁺ channels. 4. The Ca²⁺ activated K⁺ conductance is voltage dependent and changes e-fold per 31 mV membrane depolariation. 5. Extracellular tetraethylammonium, gallamine and quinidine block the Ca²⁺ activated K⁺ current. Extracellular 4-aminopyridine aminopyridine has no blocking effect. 6. Sustained injection of high amounts of Ca²⁺ irreversibly suppresses the outward current. 7. The K⁺ outward current evoked by repeated Ca²⁺ injection exhibits summation and facilitation.