ACTIVITY-DEPENDENT DEVELOPMENT OF CALCIUM REGULATION IN GROWING MOTORAXONS

Citation
Ga. Lnenicka et al., ACTIVITY-DEPENDENT DEVELOPMENT OF CALCIUM REGULATION IN GROWING MOTORAXONS, The Journal of neuroscience, 18(13), 1998, pp. 4966-4972
Citations number
47
Categorie Soggetti
Neurosciences
Journal title
ISSN journal
02706474
Volume
18
Issue
13
Year of publication
1998
Pages
4966 - 4972
Database
ISI
SICI code
0270-6474(1998)18:13<4966:ADOCRI>2.0.ZU;2-J
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+ ionophor e application, normally active tonic motor axons continue to grow, whe reas inactive phasic motor axons retract and often degenerate. To dete rmine 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+], than those from p hasic axons. When depolarized with 60 mM K+, growth cones and neurites from phasic axons had a [Ca2+], three to four times higher than did t hose from tonic axons. This difference in Ca2+ regulation includes gre ater Ca2+-handling capacity for growing tonic axons; the increase in [ Ca2+], produced by the Ca2+ ionophore 4-bromo-A23187 (0.25 mu M) is fo ur to five times greater in phasic than in tonic axons, and the declin e in [Ca2+](i) at the end of a depolarizing pulse is three to four tim es faster in tonic axons than phasic ones. Blocking impulses in growin g tonic axons for 2-3 d with tetrodotoxin reduces their capacity to re gulate [Ca2+](i). Thus, growing tonic and phasic axons have difference s in Ca2+ regulation that develop as a result of their different activ ity levels. These activity-dependent differences in Ca2+ regulation in fluence axon growth and degeneration and probably influence other neur onal processes that are mediated by changes in [Ca2+](i).