Alterations in intracellular calcium chelation reproduce developmental differences in repetitive firing and afterhyperpolarizations in rat neocortical neurons.
Many 1-week-old rat sensorimotor cortical neurons exhibit extreme spike-frequency adaptation (neurons only fire for the first 100-250 ms of a 1 s current injection) accompanied by a large, prolonged afterhyperpolarization (AHP). Relatively greater expression of a Ca-dependent K+ current appears to underlie the extreme adaptation observed in immature cells. In the present study, we examined whether altering intracellular Ca2+ buffering by introducing Ca2+ chelators via the recording electrode could reproduce the age-related differences in firing and AHPs. We studied firing behavior and AHPs in 1-week-old and adult neocortical neurons with sharp microelectrodes, under three recording conditions: no chelator, 2 mM BAPTA, or 100-200 mM BAPTA. Our principal findings in regard to firing behavior and AHPs were that (1) adult-low BAPTA neurons mimicked 1 week-control cells, (2) 1 week-high BAPTA neurons were similar to adult-control cells, (3) a greater percentage of 1 week-low BAPTA neurons showed complete adaptation, and (4) adult neurons impaled with high BAPTA electrodes fired in a burst-spiking mode. These data suggest that Ca2+ regulation is qualitatively different in immature and adult neurons.
Lorenzon
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NM
Department of Anatomy and Neurobiology, University of Tennessee-Memphis 38163, USA.
Foehring
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RC
D000200:Action Potentials / Q000187:drug effects; D000367:Age Factors; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000502:physiology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D009474:Neurons / Q000502:physiology*; D015221:Potassium Channels; D051381:Rats; D017207:Rats, Sprague-Dawley
D015221:Potassium Channels; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium