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The Journal of Neuroscience, December 15, 1998, 18(24):10652-10662

Calcium Currents of Rhythmic Neurons Recorded in the Isolated Respiratory Network of Neonatal Mice

Frank Peter Elsen and Jan-Marino Ramirez

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois 60637

To obtain a quantitative characterization of voltage-activated calcium currents in respiratory neurons, we performed voltage-clamp recordings in the transverse brainstem slice of mice from neurons located within the ventral respiratory group. It is assumed that this medullary region contains the neuronal network responsible for generating the respiratory rhythm. This study represents one of the first attempts to analyze quantitatively the currents in respiratory neurons. The inward calcium currents of VRG neurons consisted of two components: a high voltage-activated (HVA) and a low voltage-activated (LVA) calcium current. The activation threshold of the HVA current was at 40 mV. It was fully activated (peak voltage) between 10 and 0 mV. The half-maximal activation (V₅₀) was at 27.29 mV ± 1.15 (n = 24). The HVA current was inactivated completely at a holding potential of 35 mV and fully deinactivated at a holding potential of 65 mV (V₅₀, 52.26 mV ± 0.27; n = 18). The threshold for the activation of the LVA current was at 65 mV. This current had its peak voltage between 50 and 40 mV (mean, V₅₀ = 59.15 mV ± 0.21; n = 15). The LVA current was inactivated completely at a holding potential of 65 mV and deinactivated fully at a holding potential of 95 mV (mean, V₅₀ = 82.40 mV ± 0.32; n = 38). These properties are consistent with other studies suggesting that the LVA current is a T-type current. The properties of these inward currents are discussed with respect to their role in generating Ca²⁺ potentials that may contribute to the generation of the mammalian respiratory rhythm.

Key words: T-type calcium current; rhythm generation; brainstem; ventral respiratory group; medulla; breathing

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Copyright © 1998 Society for Neuroscience  0270-6474/98/182410652-11$05.00/0

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