Potassium currents in acutely isolated neurons from superficial and deep layers of the juvenile rat entorhinal cortex

Using the whole-cell configuration of the patch-clamp technique, outward K⁺ currents were recorded from acutely isolated stellate cells from superficial layers, and pyramidal cells from deep layers, of the entorhinal cortex of juvenile rats. In both cell types a fast transient and a slowly inactivating outward K⁺ current were obtained. Whereas the fast transient current (I _A) activated at potentials beyond −50 mV, the activation threshold of the slowly inactivating current (I _K) was measured at −40 mV in stellate and pyramidal cells. In stellate cells a half-maximal inactivation was estimated for I _A at −80.4 mV and for I _K at −74.6 mV, and in pyramidal cells at −81.1 mV and −71.8 mV, respectively. I _K of both cell types were reduced by tetraethylammonium (TEA) in a concentration-dependent manner. IC₅₀ values were 0.8 mM TEA for stellate cells and 1.1 mM TEA for pyramidal cells. Superfusion of 4-aminopyridine resulted in a reduction of the amplitudes of I _A and I _K as well as in an acceleration of the inactivation time constants of I _A. Extracellularly applied dendrotoxin did not have any effect on entorhinal cortex K⁺ currents. In summary, kinetic and pharmacological properties of I _A as well as of I _K are rather similar in superficial-layer stellate and deep-layer pyramidal cells acutely isolated from the entorhinal cortex of juvenile rats. Received: 20 September 1995/Received after revision: 19 March 1996/Accepted: 27 March 1996