title: Ca2+-independent muscarinic excitation of rat medial entorhinal cortex layer V neurons.
abstract: Cholinergic activation of entorhinal cortex (EC) layer V neurons plays a crucial role in the medial temporal lobe memory system and in the pathophysiology of temporal lobe epilepsy. Here, we demonstrate that muscarinic activation by focal application of carbachol depolarizes EC layer V neurons and induces epileptiform activity in rat brain slices. These seizure-like bursts are associated with a somatic [Ca2+]i increase of 293 +/- 82 nm and are blocked by the glutamate receptor antagonists CNQX and APV. Muscarinic activation did not directly evoke a [Ca2+]i increase, but subthreshold and suprathreshold depolarization did. Functional axon mapping revealed local axon branching as well as axon collaterals ascending to layers II and III. During blockade of ionotropic glutamatergic AMPA and NMDA receptors, carbachol depolarized layer V neurons by +7.5 +/- 3.4 mV. This direct muscarinic depolarization was associated with a conductance increase of 35 +/- 10.3% (+4.3 +/- 1.25 nS). Intracellular buffering of [Ca2+]i changes did not block this depolarization, but prolonged action potential duration and reduced adaptation of action potential firing. The muscarinic depolarization was neither blocked by combining intracellular Ca2+-buffering (EGTA or BAPTA) with non-specific Ca2+-channel inhibition by Ni+ (1 mm), nor by Ba2+ (1 mm) nor during inhibition of the h-current by 2 mm Cs+. In whole-cell patch-clamp recording, reversal of the muscarinic current occurred at about -45 mV and -5 mV with complete substitution of intrapipette K+ with Cs+. Thus, muscarinic depolarization of EC layer V neurons appears to be primarily mediated by Ca2+-independent activation of non-specific cation channels that conduct K+ about three times as well as Na+.
authors.affiliation: AG Molekulare Zellphysiologie, Neurowissenschaftliches Forschungszentrum der Charitè, Humboldt Universität zu Berlin, Schumannstrasse 20/21, D-10117 Berlin, Germany.
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Egorov
authors.forename: Plamena R
authors.initials: PR
authors.lastname: Angelova
authors.forename: Uwe
authors.initials: U
authors.lastname: Heinemann
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Müller
mesh_terms: D000109:Acetylcholine / Q000502:physiology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D002799:Cholinergic Fibers / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D018728:Entorhinal Cortex / Q000166:cytology / Q000187:drug effects / Q000503:physiopathology*; D004827:Epilepsy / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D004833:Epilepsy, Temporal Lobe / Q000378:metabolism / Q000503:physiopathology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009924:Organ Culture Techniques; D011188:Potassium / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D018691:Excitatory Amino Acid Antagonists; D007473:Ion Channels; D017470:Receptors, Glutamate; D011976:Receptors, Muscarinic; D002217:Carbachol; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium