Hodgkin-Huxley and partially coupled inactivation models yield different voltage dependence of block.
K+ channel blockers have been shown to exhibit complex time- and voltage-dependent effects on cardiac K+ currents. Whereas much attention has been focused on the state dependence of K+ channel block, how a particular channel model can alter the predicted time and voltage dependence of channel block remains unexplored. In this study, using two different model formalisms for the same cardiac transient outward current channel, we compare the effects of a theoretical open-state specific channel blocker on macroscopic currents. Model 1 is a Hodgkin-Huxley-like model, in which inactivation is an intrinsically voltage-dependent process and occurs independently of activation. Model 2 is a "partially coupled" model, in which inactivation is intrinsically voltage insensitive but requires channel activation before it can proceed. In the absence of drug (blocking agent), the two models reproduce the macroscopic current data. In the presence of blocking agent, the two models can differ substantially, with model 1 displaying much less block than model 2. We also examine simple mathematically convenient modifications to the Hodgkin-Huxley formalism, which reproduce some, but not all, of the use-dependent properties of block. Thus model formalism is important for analysis and simulation of state-specific drug-channel interactions.
Liu
S
S
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
Rasmusson
R L
RL
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D008955:Models, Cardiovascular; D008962:Models, Theoretical; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D011336:Probability; D013997:Time Factors
D000889:Anti-Arrhythmia Agents; D026902:Potassium Channel Blockers; D015221:Potassium Channels