Title : Simulating sodium and potassium currents in an olfactory mitral cell model
Authors : Andrew Davison, Zhishang Zhou, Michael L. Hines and Gordon M. Shepherd
Year : 2001
We have previously developed a tightly constrained model of the olfactory mitral cell based on dual patch recordings in rat olfactory bulb slices (Shen et al, J. Neurophysiol. 82: 3006-3020, 1999). The model closely simulates action potential generation at somatic and dendritic sites based on a transient Na and delayed rectifier K current. In order to extend this model for other membrane currents, we have carried out a combined experimental (patch-clamp) and modeling study. The response to long-duration, perithreshold current injection from a hyperpolarized resting potential has three main characteristics: (i) a delay of up to several hundred milliseconds before action potential firing; (ii) an inflection or overshoot in the membrane potential rise phase; (iii) subthreshold membrane potential oscillations. With suprathreshold stimulation the firing frequency increases with time, i.e. negative adaptation. These characteristics suggest the presence of a slowly-inactivating K current and a persistent Na current. We are extending the previous model in order to test these hypotheses by characterizing the membrane currents and analysing the contribution each makes to the observed behaviour. Channel kinetics and channel density distribution are obtained by fitting the model to the experimental recordings. Channel kinetics are also obtained by voltage clamp recordings and there is good agreement between the parameters obtained by the two methods. The results will lead to simulations of the firing patterns of the mitral cell over time, so that models of synaptic activation and mitral-granule cell networks can be constructed. Supported by NIDCD and NIMH (Human Brain Project).