Ca2+-activated K+ currents in rat locus coeruleus neurons induced by experimental ischemia, anoxia, and hypoglycemia.
ABSTRACT Ca2+-activated K+ currents in rat locus coeruleus neurons induced by experimental ischemia, anoxia, and hypoglycemia. J. Neurophysiol. 78: 2674-2681, 1997. The effects of metabolic inhibition on membrane currents and N-methyl--aspartic acid (NMDA)-induced currents were investigated in dissociated rat locus coeruleus (LC) neurons by using the nystatin perforated patch recording mode under voltage-clamp conditions. Changes in the intracellular Ca2+ concentration ([Ca2+]i) during the metabolic inhibition were also investigated by using the microfluometry with a fluorescent probe, Indo-1. Removal of both the oxygen and glucose (experimental ischemia), deprivation of glucose (hypoglycemia), and a blockade of electron transport by sodium cyanide (NaCN) or a reduction of the mitochondrial membrane potential with carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone(FCCP) as experimental anoxia all induced a slowly developing outward current (IOUT) at a holding potential of -40 mV. The application of 10(-4) M NMDA induced a rapid transient peak and a successive steady state inward current and a transient outward current immediately after washout. All treatments related to metabolic inhibition increased the NMDA-induced outward current(INMDA-OUT) and prolonged the one-half recovery time of INMDA-OUT. The reversal potentials of both IOUT and INMDA-OUT were close to the K+ equilibrium potential (EK) of -82 mV. Either charybdotoxin or tolbutamide inhibited the IOUT and INMDA-OUT, suggesting the contribution of Ca2+-activated and ATP-sensitive K+ channels, even though the inhibitory effect of tolbutamide gradually diminished with time. Under the metabolic inhibition, the basal level of [Ca2+]i was increased and the one-half recovery time of the NMDA-induced increase in [Ca2+]i was prolonged. The IOUT induced by NaCN was inhibited by a continuous treatment of thapsigargin but not by ryanodine, indicating the involvement of inositol 1,4, 5-trisphosphate (IP3)-induced Ca2+ release (IICR) store. These findings suggest that energy deficiency causes Ca2+ release from the IICR store and activates continuous Ca2+-activated K+ channels and transient ATP-sensitive K+ channels in acutely dissociated rat LC neurons.
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ABSTRACT: The effect of hypercapnia on outwardly-rectifying currents was examined in locus coeruleus (LC) neurons in slices from neonatal rats (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 ± 0.6mV (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 (pHo 7.00, 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 inhibition 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.AJP Regulatory Integrative and Comparative Physiology 08/2013; · 3.28 Impact Factor
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ABSTRACT: Modern society enables a shortening of sleep times, yet long-term consequences of extended wakefulness on the brain are largely unknown. Essential for optimal alertness, locus ceruleus neurons (LCns) are metabolically active neurons that fire at increased rates across sustained wakefulness. We hypothesized that wakefulness is a metabolic stressor to LCns and that, with extended wakefulness, adaptive mitochondrial metabolic responses fail and injury ensues. The nicotinamide adenine dinucleotide-dependent deacetylase sirtuin type 3 (SirT3) coordinates mitochondrial energy production and redox homeostasis. We find that brief wakefulness upregulates SirT3 and antioxidants in LCns, protecting metabolic homeostasis. Strikingly, mice lacking SirT3 lose the adaptive antioxidant response and incur oxidative injury in LCns across brief wakefulness. When wakefulness is extended for longer durations in wild-type mice, SirT3 protein declines in LCns, while oxidative stress and acetylation of mitochondrial proteins, including electron transport chain complex I proteins, increase. In parallel with metabolic dyshomeostasis, apoptosis is activated and LCns are lost. This work identifies mitochondrial stress in LCns upon wakefulness, highlights an essential role for SirT3 activation in maintaining metabolic homeostasis in LCns across wakefulness, and demonstrates that extended wakefulness results in reduced SirT3 activity and, ultimately, degeneration of LCns.Journal of Neuroscience 03/2014; 34(12):4418-31. · 6.91 Impact Factor