Kinetics and Mg2+ block of N-methyl-D-aspartate receptor channels during postnatal development of hippocampal CA3 pyramidal neurons.
Voltage-dependent magnesium block of N-methyl-D-aspartate-activated channels, and the N-methyl-D-aspartate component of excitatory synaptic currents were studied in CA3 pyramidal neurons of hippocampal slices from immature (postnatal day 3-8) and adult (postnatal day 25-60) rats. In all neurons studied the kinetics of single-channel openings in cell-attached and inside-out configurations was strongly modulated by extracellular Mg2+, in a voltage-dependent manner. No age-dependent difference in the Mg2+ sensitivity of N-methyl-D-aspartate channels was observed. At physiological concentrations of external Mg2+ (1.3 mM), N-methyl-D-aspartate components of excitatory synaptic currents measured from immature and adult rats displayed a similar voltage-dependence. In immature neurons (postnatal day 3-6), the N-methyl-D-aspartate component of excitatory postsynaptic currents decay time-course was a single-exponential with an average time-constant of about 300 ms. In neurons from older animals the decay was described by a double-exponential function with both a fast component (tau f, 54-130 ms) and a slow component (tau s, 275-400 ms). With age, the contribution of the fast component increased and the decay time-course of the N-methyl-D-aspartate component of excitatory postsynaptic currents accelerated. It is concluded that the Mg2+ block of N-methyl-D-aspartate channels in CA3 pyramidal neurons does not change with development, but the kinetic properties of N-methyl-D-aspartate receptor channels are developmentally regulated.
Khazipov
R
R
INSERM Hopital de Port-Royal, Paris, France.
Ragozzino
D
D
Bregestovski
P
P
D000367:Age Factors; D000818:Animals; D006624:Hippocampus / Q000187:drug effects*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects*
D016194:Receptors, N-Methyl-D-Aspartate; D008274:Magnesium