Hyperpolarization-activated cation currents in stellate and pyramidal neurons of rat entorhinal cortex

Properties of hyperpolarization-activated cation currents (I-h) were invest igated in neurons of juvenile rat entorhinal cortex using the patch-clamp t echnique. A rat brain slice preparation containing the entorhinal cortex wa s used for whole-cell recordings of I-h in pyramidal cells from layer IV an d in stellate cells from layer II of the entorhinal cortex. In both stellat e and pyramidal cells, I-h activated at potentials more negative than -60 m V and did not show any time-dependent inactivation. Half-maximal activation of I-h was achieved at -95.3 mV in pyramidal cells and at -95.0 mV in stel late cells. The channels were permeable for sodium and potassium ions. I-h of pyramidal and stellate neurons was reduced by about 50% in the presence of 100 mu M ZD7288. Extracellularly applied 1 mM Cs+ decreased I-h of pyram idal cells by 92%, whereas I-h of stellate cells was only reduced by 70%. I n both pyramidal and stellate neurons, I-h was not significantly changed du ring the application of 1 mM Ba2+. 8-Bromo-c-AMP increased amplitudes of I- h in stellate cells, while I-h of pyramidal cells remained unchanged. It is suggested that different types of hyperpolarization-activated cation chann els are expressed in pyramidal and stellate cells of the entorhinal cortex. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.