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+ (Kext) on Ih were investigated in CA1 pyramidal cells of rat hippocampal slices using the whole-cell patch clamp technique. At the basal Kext level (2.5 mM), hyperpolarization-activated cation current (Ih) had a maximal amplitude of −350±60 pA which was enhanced by ∼60 and ∼95% at 5 and 7.5 mM Kext, 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 ∼2.4 nS under control conditions and significantly increased to ∼3.3 and ∼5.6 nS at 5 and 7.5 mM Kext, respectively. The reversal potential was shifted in the positive direction, from a control value of ∼−30 mV by ∼6 and ∼14 mV at 5 and 7.5 mM Kext, respectively. Our data demonstrate that even moderate changes in Kext have a substantial effect on the properties of Ih. [Copyright &y& Elsevier]