Relationships between intracellular calcium and afterhyperpolarizations in neocortical pyramidal neurons.
We examined the effects of recent discharge activity on [Ca2+]i in neocortical pyramidal cells. Our data confirm and extend the observation that there is a linear relationship between plateau [Ca2+]i and firing frequency in soma and proximal apical dendrites. The rise in [Ca2+] activates K+ channels underlying the afterhyperpolarization (AHP), which consists of 2 Ca(2+)-dependent components: the medium AHP (mAHP) and the slow AHP (sAHP). The mAHP is blocked by apamin, indicating involvement of SK-type Ca(2+)-dependent K+ channels. The identity of the apamin-insensitive sAHP channel is unknown. We compared the sAHP and the mAHP with regard to: 1) number and frequency of spikes versus AHP amplitude; 2) number and frequency of spikes versus [Ca2+]i; 3) IAHP versus [Ca2+]i. Our data suggest that sAHP channels require an elevation of [Ca2+]i in the cytoplasm, rather than at the membrane, consistent with a role for a cytoplasmic intermediate between Ca2+ and the K+ channels. The mAHP channels appear to respond to a restricted Ca2+ domain.
Abel
H J
HJ
Department of Anatomy and Neurobiology, University of Tennessee, Memphis, Tennessee 38163, USA.
Lee
J C F
JC
Callaway
J C
JC
Foehring
R C
RC
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001030:Apamin / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D003712:Dendrites / Q000187:drug effects / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods; D005110:Extracellular Space / Q000187:drug effects / Q000502:physiology*; D016257:Fura-2 / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019579:Neocortex / Q000166:cytology*; D018408:Patch-Clamp Techniques / Q000379:methods; D017966:Pyramidal Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D000318:Adrenergic beta-Agonists; D002104:Cadmium; D001030:Apamin; D007545:Isoproterenol; D002118:Calcium; D016257:Fura-2