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

Abstract

Properties of hyperpolarization-activated cation currents ( I h) were investigated in neurons of juvenile rat entorhinal cortex using the patch–clamp technique. A rat brain slice preparation containing the entorhinal cortex was used for whole-cell recordings of I h in pyramidal cells from layer IV and in stellate cells from layer II of the entorhinal cortex. In both stellate and pyramidal cells, I h activated at potentials more negative than −60 mV 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 stellate 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 μM ZD7288. Extracellularly applied 1 mM Cs + decreased I h of pyramidal cells by 92%, whereas I h of stellate cells was only reduced by 70%. In both pyramidal and stellate neurons, I h was not significantly changed during the application of 1 mM Ba 2+. 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 channels are expressed in pyramidal and stellate cells of the entorhinal cortex.