IhEqualizes Membrane Input Resistance in a Heterogeneous Population of Fusiform Neurons in the Dorsal Cochlear Nucleus.
In a neuronal population, several combinations of its ionic conductances are used to attain a specific firing phenotype. Some neurons present heterogeneity in their firing, generally produced by expression of a specific conductance, but how additional conductances vary along in order to homeostatically regulate membrane excitability is less known. Dorsal cochlear nucleus principal neurons, fusiform neurons, display heterogeneous spontaneous action potential activity and thus represent an appropriate model to study the role of different conductances in establishing firing heterogeneity. Particularly, fusiform neurons are divided into quiet, with no spontaneous firing, or active neurons, presenting spontaneous, regular firing. These modes are determined by the expression levels of an intrinsic membrane conductance, an inwardly rectifying potassium current (IKir). In this work, we tested whether other subthreshold conductances vary homeostatically to maintain membrane excitability constant across the two subtypes. We found thatIhexpression covaries specifically withIKirin order to maintain membrane resistance constant. The impact ofIhon membrane resistance is dependent on the level ofIKirexpression, being much smaller in quiet neurons with biggerIKir, butIhvariations are not relevant for creating the quiet and active phenotypes. Finally, we demonstrate that the individual proportion of each conductance, and not their absolute conductance, is relevant for determining the neuronal firing mode. We conclude that in fusiform neurons the variations of their different subthreshold conductances are limited to specific conductances in order to create firing heterogeneity and maintain membrane homeostasis.
Department of Physiology, Ribeirão Preto Medical School, School of Medicine, University of São PauloRibeirão Preto, Brazil; Department of Physics, School of Philosophy, Sciences and Letters, University of São PauloRibeirão Preto, Brazil.
Cesar C
CC
Ceballos
Department of Otolaryngology, School of Medicine, University of Pittsburgh, Pittsburgh PA, USA.
Shuang
S
Li
Department of Physics, School of Philosophy, Sciences and Letters, University of São Paulo Ribeirão Preto, Brazil.
Antonio C
AC
Roque
Department of Otolaryngology, School of Medicine, University of Pittsburgh, PittsburghPA, USA; Department of Neurobiology, School of Medicine, University of Pittsburgh, PittsburghPA, USA.
Thanos
T
Tzounopoulos
Department of Physiology, Ribeirão Preto Medical School, School of Medicine, University of São PauloRibeirão Preto, Brazil; Department of Otolaryngology, School of Medicine, University of Pittsburgh, PittsburghPA, USA.
Ricardo M
RM
Leão
cochlear nucleus; membrane resistance; subthreshold conductances