Effects of glucose deprivation on NMDA-induced current and intracellular Ca2+ in rat substantia nigra neurons.
1. The effects of glucose deprivation on N-methyl-D-asparate (NMDA)-induced current (INMDA) and the intracellular free Ca2+ concentration ([Ca2+]i) in the acutely dissociated rat substantia nigra neurons were investigated using the nystatin-perforated patch-clamp technique under voltage clamp and the microfluometry with a fluorescent probe, Indo-1. 2. Application of NMDA induced a peak and a successive steady-state inward current, and an outward current immediately after washout at a holding potential of -40 mV. The amplitudes of the three current components of INMDA were increased by increasing the concentrations of NMDA with half-maximum concentrations (EC50s) of 1.1 x 10(-4) M, 1.2 x 10(-4) M, and 1.6 x 10(-4) M, respectively. 3. The reversal potentials of the peak inward and outward currents were -4 +/- 3 (SE) mV and -76 +/- 2 mV, respectively. The latter was close to the theoretical K+ equilibrium potential (-82 mV). 4. The outward current was potentiated by increase in extracellular Ca2+ concentration and was blocked by Cs+ internal solution and suppressed by 5 x 10(-3) M tetraethylammonium chloride and 10(-7) M charybdotoxin, indicating that it was Ca(2+)-activated K+ current. 5. Application of NMDA increased [Ca2+]i in a concentration-dependent manner with an EC50 of 3.9 x 10(-5) M. 6. Depriving the external solution of glucose induced a slowly developing outward current and increased the basal level of [Ca2+]i. It also prolonged the NMDA-induced outward current without affecting the peak inward current, and prolonged the NMDA-induced increase in [Ca2+]i without changing the peak [Ca2+]i. 7. These findings suggest that the deprivation of glucose did not affect the NMDA-induced influx of Ca2+ into the cells, but it inhibited Ca2+ clearance by affecting the efflux of Ca2+ to the extracellular space, reuptake into the intracellular Ca2+ stores, and/or active extrusion from intracellular stores.
Nakashima
Y
Y
Department of Anesthesiology, Kyushu University, Fukuoka, Japan.
Ishibashi
H
H
Harata
N
N
Akaike
N
N
D000818:Animals; D004195:Disease Models, Animal; D005947:Glucose / Q000172:deficiency*; D002546:Ischemic Attack, Transient / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D015221:Potassium Channels; D016202:N-Methylaspartate; D005947:Glucose