Dependence of calcium influx in neocortical cells on temporal structure of depolarization, number of spikes, and blockade of NMDA receptors.
Increase of intracellular [Ca(2+)] evoked by action potentials in a cell can induce long-term synaptic plasticity even without concomitant presynaptic stimulation. We used optical recording of the fluorescence of a Ca(2+)-indicator Oregon Green to investigate whether differences in results obtained with modifications of that purely postsynaptic induction protocol could be due to differential Ca(2+) influx. We compared changes of the somatic [Ca(2+)] in layer II-III pyramidal cells in slices of rat visual cortex evoked by bursts of depolarization pulses and long depolarizing steps. During weak depolarizations, the Ca(2+) influx was proportional to the amplitude and duration of the depolarization. With suprathreshold depolarizations, the Ca(2+) influx was proportional to the number of action potentials. Because the burst depolarizations evoked more spikes than did the long duration steps, this burst protocol led to a larger Ca(2+) influx. With all stimulation protocols, the spike-induced Ca(2+) influx was reduced during blockade of N-methyl-D-aspartate (NMDA) receptors. Differences in intracellular [Ca(2+)] increases thus may be one reason for differential effects of purely postsynaptic challenges on synaptic transmission.
Balaban
Pavel
P
Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia.
Chistiakova
Marina
M
Malyshev
Aleksey
A
Volgushev
Maxim
M
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation / Q000379:methods; D005456:Fluorescent Dyes / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009930:Organic Chemicals; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014793:Visual Cortex / Q000166:cytology*
D005456:Fluorescent Dyes; C403124:Oregon Green BAPTA-dextran; D009930:Organic Chemicals; D016194:Receptors, N-Methyl-D-Aspartate; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; D002118:Calcium