title: Facilitation of somatic calcium channels can evoke prolonged tail currents in rat hypoglossal motoneurons.
abstract: Voltage-dependent persistent inward currents (PICs) make an important contribution to the input-output properties of alpha motoneurons. PICs are thought to be mediated by membrane channels located primarily on the dendrites as evidenced by prolonged tail currents following the termination of a voltage step and by a clockwise hysteresis in the whole cell inward currents recorded in response to depolarizing then repolarizing voltage ramp commands. We report here, however, that voltage-clamp currents with these same features can be generated in isolated somatic membrane patches from rat hypoglossal motoneurons. Long-lasting (200-800 ms) tail currents after 1-s voltage-clamp pulses were observed in nucleated patches from 16 of 23 cells. Further, these somatic PICs display "facilitation" in response to conditioning depolarization as previously observed in whole cell recordings from intact neurons. Pharmacological tests suggest that the PICs were primarily mediated by Cav1 channels. Our results show that many of the features of persistent calcium currents recorded from intact motoneurons do not necessarily reflect a remote dendritic origin but can also be ascribed to the intrinsic properties of their Cav1 channels.
authors.affiliation: Department of Physiology and Biophysics,School of Medicine, University of Washington, Seattle, Washington 98195-7290, USA.
authors.forename: Anna T
authors.initials: AT
authors.lastname: Moritz
authors.forename: Gregory
authors.initials: G
authors.lastname: Newkirk
authors.forename: Randall K
authors.initials: RK
authors.lastname: Powers
authors.forename: Marc D
authors.initials: MD
authors.lastname: Binder
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002467:Cell Nucleus / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004553:Electric Conductivity; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D007002:Hypoglossal Nerve / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D009046:Motor Neurons / Q000166:cytology* / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D011758:Pyrroles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011758:Pyrroles; C071658:FPL 64176