Pharmacological properties of the potassium-activated inward current in pyramidal hippocampal neurons

Abstract

Elevation of the external potassium concentration induced a two-phase inward current in freshly isolated pyramidal hippocampal neurons. This current was voltage-dependent and demonstrated strong inward rectification. The current consisted of a leakage current and a time-dependent current (τ=40–50 msec at 21°C); the latter was designated asI ΔK. As was shown earlier, K+ is a major charge carrier in the development of slow potassium-activated current. The pharmacological properties ofI ΔK were studied using a patch-clamp technique.I ΔK was completely blocked by external 10 mM TEA or 5 mM Ba2+ (IC50=480±90mM) and exhibited low sensitivity to extracellular Cs+ (2 mM). This current was not affected by 1 mM 4-aminopyridine and was insensitive to a muscarinic agonist, carbachol (50 μM), and to 1 mM extracellular Cd2+. Elevation of external Ca2+ from 2.5 mM to 10 mM did not changeI ΔK. Our data indicate that the pharmacological properties ofI ΔK differ from those of other voltage-gated potassium currents, but more specific blockers must be used to make this evidence conclusive.