title: Activity-dependent initiation of a prolonged depolarization in aplysia bag cell neurons: role for a cation channel.
abstract: The translation of prior activity into changes in excitability is essential for memory and the initiation of behavior. After brief synaptic input, the bag cell neurons of Aplysia californica undergo a nearly 30-min afterdischarge to release egg-laying hormone. The present study examines a prolonged depolarization in cultured bag cell neurons. A 5-Hz, 10-s action potential train elicited a depolarization of about 10 mV, which lasted </=30 min and was reduced by calmodulin kinase inhibition. Very broad action potentials (resulting from TEA application) decreased prolonged depolarization amplitude, indicating that strong Ca(2+) influx did not necessarily promote the response. The prolonged depolarization current (I(PD)) was recorded after 5-Hz, 10-s trains of square voltage pulses of varying duration (10-150 ms). Despite Ca(2+) influx increasing steadily with pulse duration, I(PD) was most reliably initiated at 100 ms, suggesting a Ca(2+) window or limit exists for triggering I(PD). Consistent with this, modestly broader action potentials, evoked by lengthening the train current-pulse duration, resulted in smaller prolonged depolarizations. With respect to the properties of I(PD), it displayed a linear current-voltage relationship with a reversal potential of about -45 mV that was shifted to approximately -25 mV by lowering internal K(+) or about -56 mV by lowering external Na(+) and Ca(2+). I(PD) was blocked by Gd(3+), but was not antagonized by MDL-123302A, SKF-96365, 2-APB, tetrodotoxin, or flufenamic acid. Optimal Ca(2+) influx may activate calmodulin kinase and a voltage-independent, nonselective cation channel to initiate the prolonged depolarization, thereby contributing to the afterdischarge and reproduction.
authors.affiliation: Department of Physiology, Queen's University, 4th Floor, Botterell Hall, 18 Stuart Street, Kingston, ON, K7L 3N6, Canada.
authors.forename: Anne Y
authors.initials: AY
authors.lastname: Hung
authors.forename: Neil S
authors.initials: NS
authors.lastname: Magoski
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001048:Aplysia / Q000166:cytology*; D002148:Calmodulin-Binding Proteins / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004533:Egtazic Acid / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D049990:Membrane Transport Modulators / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002148:Calmodulin-Binding Proteins; D002412:Cations; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007473:Ion Channels; D049990:Membrane Transport Modulators; D026902:Potassium Channel Blockers; D004533:Egtazic Acid; C063302:KN 62; D019789:Tetraethylammonium; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine