Use Dependent Attenuation of Rat HCN1-Mediated Ih in Intact HEK293 Cells

Background/Aims: Cationic currents (I-h) through the fast activating and relatively cAMP insensitive subtype of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, HCN1, are limited by cytosolic factors in mammalian cells. This cytosolic HCN1 break is boosted by changes in membrane voltage that are not characterized on a biophysical level, yet. Methods: We overexpressed rat (r)HCN1 in human embryonic kidney cells (HEK293) and recorded pharmacologically isolated I-h in cell-attached or whole-cell mode of the patch-clamp technique. Results: Recurring activation of rHCN1 reduced and slowed thin intact HEK293 cells (cell-attached mode). On the contrary, sustained disruption of the intracellular content (whole cell mode) ceased activity dependence and partially enables voltage dependent hysteresis. The activity induced I-h attenuation in intact cells was independent of the main external cation, depended on the number of previous forced activations and was - at least in part - due to a shift in the voltage dependence of activation towards hyperpolarization as estimated by an adapted tail current analysis. Intracellular elevation of cAMP could not reverse the changes in I-h. Conclusion: Reduction of rHCN1 mediated I-h is use dependent and may involve the coupling of voltage sensor and pore. (C) 2016 The Author(s) Published by S. Karger AG, Basel