Transient outwardly rectifying A currents are involved in the firing rate response to altered CO2 in chemosensitive locus coeruleus neurons from neonatal rats.
The effect of hypercapnia on outwardly rectifying currents was examined in locus coeruleus (LC) neurons in slices from neonatal rats [postnatal day 3 (P3)-P15]. Two outwardly rectifying currents [4-aminopyridine (4-AP)-sensitive transient current and tetraethyl ammonium (TEA)-sensitive sustained current] were found in LC neurons. 4-AP induced a membrane depolarization of 3.6 ± 0.6 mV (n = 4), while TEA induced a smaller membrane depolarization of 1.2 ± 0.3 mV (n = 4). Hypercapnic acidosis (HA) inhibited both currents. The maximal amplitude of the TEA-sensitive current was reduced by 52.1 ± 4.5% (n = 5) in 15% CO2 [extracellular pH (pHo) 7.00, intracellular pH (pHi) 6.96]. The maximal amplitude of the 4-AP-sensitive current was reduced by 34.5 ± 3.0% (n = 6) in 15% CO2 (pHo 7.00, pHi 6.96), by 29.4 ± 6.8% (n = 6) in 10% CO2 (pHo 7.15, pHi 7.14), and increased by 29.0 ± 6.4% (n = 6) in 2.5% CO2 (pHo 7.75, pHi 7.35). 4-AP completely blocked hypercapnia-induced increased firing rate, but TEA did not affect it. When LC neurons were exposed to HA with either pHo or pHi constant, the 4-AP-sensitive current was inhibited. The data show that the 4-AP-sensitive current (likely an A current) is inhibited by decreases in either pHo or pHi. The change of the A current by various levels of CO2 is correlated with the change in firing rate induced by CO2, implicating the 4-AP-sensitive current in chemosensitive signaling in LC neurons.
Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio.
Ke-Yong
KY
Li
Robert W
RW
Putnam
D000138:Acidosis / Q000378:metabolism / Q000503:physiopathology; D000818:Animals; D000831:Animals, Newborn; D002245:Carbon Dioxide / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D005071:Evoked Potentials; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology; D016857:Hypocapnia / Q000378:metabolism / Q000503:physiopathology; D066298:In Vitro Techniques; D007700:Kinetics; D008125:Locus Coeruleus / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D002245:Carbon Dioxide
A current; carbon dioxide; central control of breathing; neuronal acid sensing; potassium channels