K+-induced changes in the properties of the hyperpolarization-activated cation current Ih in rat CA1 pyramidal cells

The effects of rises in external K+ (K-ext) on 1(h) were investigated in CA1 pyramidal cells of rat hippocampal slices using the whole-cell patch clamp technique. At the basal K-ext level (2.5 mM), hyperpolarization-activated cation current (1(h)) had a maximal amplitude of -350 +/- 60 pA which was enhanced by similar to60 and similar to95% at 5 and 7.5 mM K-ext, respectively. The midpoint activation voltage was significantly shifted from -80 mV in the negative direction to about -87 mV at both 5 and 7.5 mM Kext, without appreciable alterations of the current kinetics. The maximal conductance was similar to2.4 nS under control conditions and significantly increased to similar to3.3 and similar to5.6 nS at 5 and 7.5 mM K-ext, respectively. The reversal potential was shifted in the positive direction, from a control value of similar to-30 mV by similar to6 and similar to14 mV at 5 and 7.5 mM K-ext, respectively. Our data demonstrate that even moderate changes in K-ext have a substantial effect on the properties of 1(h). (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.