Membrane resistivity estimated for the Purkinje neuron by means of a passive computer model

A multicompartment passive electrotonic computer model is constructed for the cerebellar Purkinje cell of the guinea-pig. The model has 1089 coupled compartments to accurately represent the morphology of the Purkinje cell. In order that the calculated behavior of the model fit the published electrophysiological observations of somatic and dendritic input conductance, the neural membrane resistivity must be spatially non-uniform. The passive electrical parameter values for which the model best fits the observations of input conductances, pulse attenuation and current-clamp voltage transients are rm,dend = 45,740 omega cm2, rm,soma = 760 omega cm2, ri = 225 omega cm and cm = 1.16 microF/cm2 (the membrane and cytoplasm specific resistivities and membrane specific capacitance, respectively). The model with these parameter values is electrically compact, with electrotonic length X = 0.33 and dendritic dominance ratio p = 0.44. Analysis of the calculated voltage transient of the multicompartment model by the methods of equivalent-cylinder cable theory is shown to result in very different and unreliable conclusions. The significance for neuronal function of the estimated electrical parameter values is discussed. The possible effect of active conductances on these conclusions is assessed.