Modeling of single noninactivating Na+ channels: evidence for two open and several fast inactivated states.
Voltage-gated Na(+) channels play a fundamental role in the excitability of nerve and muscle cells. Defects in fast Na(+) channel inactivation can cause hereditary muscle diseases with hyper- or hypoexcitability of the sarcolemma. To explore the kinetics and gating mechanisms of noninactivating muscle Na(+) channels on a molecular level, we analyzed single channel currents from wild-type and five mutant Na(+) channels. The mutations were localized in different protein regions which have been previously shown to be important for fast inactivation (D3-D4-linker, D3/S4-S5, D4/S4-S5, D4/S6) and exhibited distinct grades of defective fast inactivation with varying levels of persistent Na(+) currents caused by late channel reopenings. Different gating schemes were fitted to the data using hidden Markov models with a correction for time interval omission and compared statistically. For all investigated channels including the wild-type, two open states were necessary to describe our data. Whereas one inactivated state was sufficient to fit the single channel behavior of wild-type channels, modeling the mutants with impaired fast inactivation revealed evidence for several inactivated states. We propose a single gating scheme with two open and three inactivated states to describe the behavior of all five examined mutants. This scheme provides a biological interpretation of the collected data, based on previous investigations in voltage-gated Na(+) and K(+) channels.
The
Yu-Kai
YK
Institut für Physik, Freiburger Zentrum für Datenanalyse und Modellbildung, Universität Freiburg, Freiburg, Germany.
Fernandes
Jacqueline
J
Popa
M Oana
MO
Alekov
Alexi K
AK
Timmer
Jens
J
Lerche
Holger
H
D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003198:Computer Simulation; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007668:Kidney / Q000502:physiology*; D008954:Models, Biological; D008956:Models, Chemical; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism*; D062553:NAV1.4 Voltage-Gated Sodium Channel; D012964:Sodium / Q000737:chemistry / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism*
D009124:Muscle Proteins; D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human; D015222:Sodium Channels; D012964:Sodium