Novel transient outward K + current of mature murine hippocampal neurones

Hippocampal neurones were freshly isolated from the brain of adult mice and voltage-dependent K+ currents were recorded with the whole-cell patch-clamp technique. Three components of transient K+ current (IA) were isolated when analyzing data with exponential functions or treating neurones with a variety of voltage protocols and pharmacologic agents. Subtraction of the delayed rectifier current (I K) from the K+ currents elicited after prepulses to –120 mV of varying duration revealed fast (IAf) and slow (IAs) components with decay time constants of 45 ± 8 and 612 ± 140 ms, respectively; the corresponding time constants for the removal of inactivation were 12.3 and 189.6 ms. Both tetraethylammonium and dendrotoxin selectively inhibited IAs. 4-Aminopyridine (4-AP) specifically blocked IAf and 40% of IAs with different affinities. Therefore, the properties of a 4-AP-resistant (IAsR) and a 4-AP-sensitive (IAsS) component of IAs were compared. These data suggest that three distinct subtypes of K+ currents contribute to the IA of mature murine hippocampal neurones.