Role of Potassium Conductances in Determining Input Resistance of Developing Brain Stem Motoneurons

• Published in: Journal of neurophysiology 2000-11, Vol.84 (5), p.2330-2339
• Main Authors: Cameron, William E, Nunez-Abades, Pedro A, Kerman, Ilan A, Hodgson, Tracy M
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Barium - pharmacology; Brain Stem - cytology; Brain Stem - growth & development; Brain Stem - physiology; Cesium - pharmacology; Electric Impedance; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Magnesium - pharmacology; Male; Motor Neurons - chemistry; Motor Neurons - physiology; Potassium - metabolism; Potassium Channels - physiology; Rats; Rats, Sprague-Dawley; Tetraethylammonium - pharmacology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.84.5.2330

  1 Department of Neuroscience and   2 Department of Psychiatry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260; and   3 Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97201 Cameron, William E., Pedro A. Núñez-Abades, Ilan A. Kerman, and Tracy M. Hodgson. Role of Potassium Conductances in Determining Input Resistance of Developing Brain Stem Motoneurons. J. Neurophysiol. 84: 2330-2339, 2000. The role of potassium conductances in determining input resistance was studied in 166 genioglossal (GG) motoneurons using sharp electrode recording in brain stem slices of the rats aged 5-7 days, 13-15 days, and 19-24 days postnatal ( P ). A high magnesium (Mg 2+ ; 6 mM) perfusate was used to block calcium-mediated synaptic release while intracellular or extracellular cesium (Cs + ) and/or extracellular tetraethylammonium (TEA) or barium (Ba 2+ ) were used to block potassium conductances. In all cases, the addition of TEA to the high Mg 2+ perfusate generated a larger increase in both input resistance ( R n ) and the first membrane time constant ( 0 ) than did high Mg 2+ alone indicating a substantial nonsynaptic contribution to input resistance. With intracellular injection of Cs + , GG motoneurons with lower resistance (40 M ). There was also a significant increase in the effect of internal Cs + on R n and 0 with age. The largest percent increase (67%) in the 0 due to intracellular Cs + occurred at P13-15, a developmental stage characterized by a large reduction in specific membrane resistance. Addition of external Cs + blocked conductances (further increasing R n and 0 ) beyond those blocked by the TEA perfusate. Substitution of external calcium with 2 mM barium chloride produced a significant increase in both R n and 0 at all ages studied. The addition of either intracellular Cs + or extracellular Ba 2+ created a depolarization shift of the membrane potential. The amount of injected current required to maintain the membrane potential was negatively correlated with the control R n of the cell at most ages. Thus low resistance cells had, on the average, more Cs + - and Ba 2+ -sensitive channels than their high resistance counterparts. There was also a disproportionately larger percent increase in 0 as compared with R n for both internal Cs + and external Ba 2+ . Based on a model by Redman and colleagues, it mig