title: Activity-dependent development of calcium regulation in growing motor axons.
abstract: In cultured nerve cord explants from the crayfish (Procambarus clarkii), the normal impulse activity levels of growing motor axons determine their response to Ca2+ influx. During depolarization or Ca2+ ionophore application, normally active tonic motor axons continue to grow, whereas inactive phasic motor axons retract and often degenerate. To determine the role of Ca2+ regulation in this difference, we measured the intracellular free Ca2+ concentration ([Ca2+]i) with fura-2. Growth cones from tonic axons normally had a higher [Ca2+]i than those from phasic axons. When depolarized with 60 mM K+, growth cones and neurites from phasic axons had a [Ca2+]i three to four times higher than did those from tonic axons. This difference in Ca2+ regulation includes greater Ca2+-handling capacity for growing tonic axons; the increase in [Ca2+]i produced by the Ca2+ ionophore 4-bromo-A23187 (0.25 microM) is four to five times greater in phasic than in tonic axons, and the decline in [Ca2+]i at the end of a depolarizing pulse is three to four times faster in tonic axons than phasic ones. Blocking impulses in growing tonic axons for 2-3 d with tetrodotoxin reduces their capacity to regulate [Ca2+]i. Thus, growing tonic and phasic axons have differences in Ca2+ regulation that develop as a result of their different activity levels. These activity-dependent differences in Ca2+ regulation influence axon growth and degeneration and probably influence other neuronal processes that are mediated by changes in [Ca2+]i.
authors.affiliation: Neurobiology Research Center, Department of Biological Sciences, University at Albany, State University of New York, Albany, New York 12222, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Lnenicka
authors.forename: K F
authors.initials: KF
authors.lastname: Arcaro
authors.forename: J M
authors.initials: JM
authors.lastname: Calabro
mesh_terms: D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000187:drug effects / Q000502:physiology; D000001:Calcimycin / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D016257:Fura-2; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000378:metabolism* / Q000648:ultrastructure; D009420:Nervous System / Q000166:cytology; D016501:Neurites / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D005456:Fluorescent Dyes; D007476:Ionophores; D000001:Calcimycin; D013779:Tetrodotoxin; C033170:4-bromo-A-23187; D002118:Calcium; D016257:Fura-2