Whole-cell NMDA-evoked current in suprachiasmatic neurones of the rat: modulation by extracellular calcium ions

Autor: Jean Jacques Dreifuss, Stefano Alberi, Michel Dubois-Dauphin, Mario Raggenbass
Rok vydání: 1997
Předmět:
Male
Patch-Clamp Techniques
Extracellular Space/drug effects/metabolism
N-Methylaspartate/ pharmacology
Ion Channels
Membrane Potentials
Rats
Sprague-Dawley
chemistry.chemical_compound
Suprachiasmatic Nucleus/drug effects/ metabolism
Excitatory Amino Acid Agonists
Magnesium
Egtazic Acid
Chelating Agents
Membrane potential
Neurons
General Neuroscience
Neurons/drug effects/ metabolism
Calcium/ physiology
NMDA receptor
Suprachiasmatic Nucleus
Ion Channel Gating
Membrane Potentials/drug effects/physiology
Excitatory Amino Acid Agonists/ pharmacology
medicine.medical_specialty
N-Methylaspartate
Egtazic Acid/analogs & derivatives/pharmacology
chemistry.chemical_element
Calcium
In Vitro Techniques
Slice preparation
BAPTA
Internal medicine
medicine
Animals
Channel blocker
Patch clamp
Molecular Biology
Ion Channels/drug effects/ metabolism
Magnesium/physiology
Ion Channel Gating/drug effects
ddc:616.8
Rats
Electrophysiology
Endocrinology
chemistry
nervous system
Biophysics
Neurology (clinical)
Extracellular Space
Chelating Agents/pharmacology
Developmental Biology
Zdroj: Brain Research, Vol. 745, No 1-2 (1997) pp. 55-66
ISSN: 0006-8993
Popis: The action of N-methyl-D-aspartic acid (NMDA) on suprachiasmatic neurones was studied using whole-cell recordings in coronal hypothalamic slices of the rat. The location of the recorded neurones within the suprachiasmatic nucleus was ascertained by intracellular labelling with biocytin, followed by histological processing of the slice. Suprachiasmatic neurones had an input resistance of 780 +/- 20 M omega (mean +/- S.E.M.; n = 106). They were voltage-clamped at or near their resting membrane potential and their responsiveness to NMDA was tested by adding this compound to the perfusion solution. NMDA generated an inward current in about 85% of the neurones. At 50 microM, the average induced peak current was 30 +/- 10 pA (n = 32); at 100 microM, it was 50 +/- 10 pA (n = 12). The NMDA-induced current was reduced by D-2-amino-5-phosphopentanoic acid (D-AP5), and NMDA receptor antagonist, and was suppressed by MK-801, and NMDA channel blocker. Reducing the extracellular magnesium concentration from 1 to 0.01 mM caused a 2- to 3-fold increase in the amplitude of this current. Thus, suprachiasmatic neurones are endowed with functional NMDA receptor-channels, which may play a role in glutaminergic transmission in this nucleus. Decreasing the extracellular calcium concentration from 2 to 0.01 mM caused a 1.3- to 4.5-fold enhancement in the whole-cell NMDA current. This effect was probably not mediated by a change in the intracellular free calcium concentration. Indeed, loading suprachiasmatic neurones with 11 or 20 mM of the calcium chelator, 1,2-bis(2- aminophenoxy)ethane-N,N,N',N'-tetracetic acid (BAPTA) suppressed a calcium-dependent slowly decaying outward aftercurrent but did not affect the low-calcium-induced facilitation of the NMDA response. NMDA current-voltage relations were established in normal and low-calcium perfusion solutions. In the normal solution, the net current generated by NMDA contained a region of negative slope conductance and reversed in polarity at 7 +/- 2 mV. In the low-calcium solution, this current increased in amplitude in the region of negative slope conductance, whereas at more depolarized potentials it was not altered. The NMDA-induced current was fitted using the Boltzmann equation. The effect of a low-calcium solution could be modelled by shifting the activation of the NMDA-sensitive conductance in the negative direction, by about 17 mV. We conjecture that lowering external calcium can unmask negative surface charges located on or near the NMDA channel and that this, in turn, weakens the voltage-dependent block of the channel by magnesium. A voltage-dependent blockade of the NMDA channel by calcium, however, may be also contribute to this effect. This low-calcium-induced facilitation of the NMDA response could play a regulatory role by enhancing calcium influx through the NMDA channel in case of calcium depletion in its vicinity.
Databáze: OpenAIRE
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