title: Dynamic control of presynaptic Ca(2+) inflow by fast-inactivating K(+) channels in hippocampal mossy fiber boutons.
abstract: Analysis of presynaptic determinants of synaptic strength has been difficult at cortical synapses, mainly due to the lack of direct access to presynaptic elements. Here we report patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampal slices. The presynaptic action potential is very short during low-frequency stimulation but is prolonged up to 3-fold during high-frequency stimulation. Voltage-gated K(+) channels in MFBs inactivate rapidly but recover from inactivation very slowly, suggesting that cumulative K(+) channel inactivation mediates activity-dependent spike broadening. Prolongation of the presynaptic voltage waveform leads to an increase in the number of Ca(2+) ions entering the terminal per action potential and to a consecutive potentiation of evoked excitatory postsynaptic currents at MFB-CA3 pyramidal cell synapses. Thus, inactivation of presynaptic K(+) channels contributes to the control of efficacy of a glutamatergic synapse in the cortex.
authors.affiliation: Physiologisches Institut der Universität Freiburg, Hermann-Herder-Str. 7, D-79104, Freiburg, Germany.
authors.forename: J R
authors.initials: JR
authors.lastname: Geiger
authors.forename: P
authors.initials: P
authors.lastname: Jonas
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004546:Elapid Venoms / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D019599:Mossy Fibers, Hippocampal / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D004546:Elapid Venoms; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D018698:Glutamic Acid; D013779:Tetrodotoxin; D019789:Tetraethylammonium; C020273:dendrotoxin; D002118:Calcium