We found that HCN2 and HCN4 channels expressed in oocytes from the frog Xenopus laevis do not display the activation kinetic changes that we (previously) observed in spHCN and HCN1. However, HCN2 and HCN4 channels display changes in their tail currents, suggesting that these channels also undergo mode shifts and that the conformational changes underlying the mode shifts are due to conserved aspects of HCN channels. With computer modelling, we show that in channels with relatively slow opening kinetics and fast mode-shift transitions, such as HCN2 and HCN4 channels, the mode shift effects are not readily observable, except in the tail kinetics. Computer simulations of sino-atrial node action potentials suggest that the HCN2 channel, together with the HCN1 channel, are important regulators of the heart firing frequency and that the mode shift is an important property to prevent arrhythmic firing. We conclude that although all HCN channels appear to undergo mode shifts – and thus may serve to prevent arrhythmic firing – it is mainly observable in ionic currents from HCN channels with faster kinetics. See papers for more and details.
Model Type: Channel/Receptor
Simulation Environment: QBasic/QuickBasic/Turbo Basic/VBA
Implementer(s): Elinder, Fredrik [fredrik.elinder at ibk.liu.se]
Elinder F, Männikkö R, Pandey S, Larsson HP. (2006). Mode shifts in the voltage gating of the mouse and human HCN2 and HCN4 channels. The Journal of physiology. 575 [PubMed]
Männikkö R, Pandey S, Larsson HP, Elinder F. (2005). Hysteresis in the voltage dependence of HCN channels: conversion between two modes affects pacemaker properties. The Journal of general physiology. 125 [PubMed]