Roles of a potassium afterhyperpolarization current in generating neuromagnetic fields and field potentials in longitudinal CA3 slices of the guinea-pig.
OBJECTIVE
Roles of a calcium-dependent potassium conductance of slow afterhyperpolarization (AHP) type (gK(AHP)) in generating magnetoencephalographic (MEG) signals were studied in hippocampal longitudinal CA3 slices of the guinea pig.


METHODS
The roles of gK(AHP) were experimentally inferred from effects of its blocker, carbamylcholine-chloride (carbachol, CCh), on MEG signals. The MEG signals were compared with extracellular field potentials and intracellular potentials of the pyramidal cells in the slice.


RESULTS
CCh profoundly affected MEG waveforms. CCh reduced the initial spike of the evoked MEG signals independently of stimulation of the cell layer and apical dendrites. The slow wave of the evoked MEG signals was reduced by the somatic stimulation, but was enhanced by the apical stimulation. Elevated extracellular calcium and bath-applied tetraethylammonium (TEA) enhanced the CCh effects. CCh also increased spontaneous MEG signals. These effects on MEG and field potentials could be interpreted on the basis of synaptic and intracellular effects of CCh.


CONCLUSIONS
Our results indicate that abnormality in this subtle calcium-dependent potassium channel may profoundly influence MEG and EEG signals.
Wu
J
J
Department of Neurology and Neurosciences, University of New Mexico School of Medicine, Albuquerque 87131, USA.
Okada
Y C
YC
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D004569:Electroencephalography / Q000187:drug effects*; D004574:Electromagnetic Fields; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D015225:Magnetoencephalography; D018721:Muscarinic Agonists / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D010812:Physical Stimulation; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D018721:Muscarinic Agonists; D018722:Nicotinic Agonists; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002217:Carbachol