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The Journal of Neuroscience, January 1, 2002, 22(1):73-81

Activity- and Target-Dependent Regulation of Large-Conductance Ca²⁺-Activated K⁺ Channels in Developing Chick Lumbar Motoneurons

Miguel Martin-Caraballo and Stuart E. Dryer

Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5513

The functional expression of large-conductance (BK-type) Ca²⁺-activated K⁺ (K_Ca) channels was examined in developing chick lumbar motoneurons (LMNs) between embryonic day 6 (E6) and E13 using patch-clamp recording techniques. The macroscopic K_Ca current of E13 LMNs is inhibited by iberiotoxin and resistant to apamin. The average macroscopic K_Ca density was low before E8 and increased 3.3-fold by E11, with an additional 1.8-fold increase occurring by E13. BK-type K_Ca channels could not be detected in inside-out patches from E8 LMNs but were readily detected at E11. The density of voltage-activated Ca²⁺ currents did not change between E8 and E11. Surgical ablation of target tissues at E5 caused a significant reduction in average K_Ca density in LMNs measured at E11. Conversely, chronic in ovo administration of D-tubocurarine, which causes an increase in motoneuron branching on the surface of the muscle target tissue, evoked a 1.8-fold increase in average LMN K_Ca density measured at E11. Electrical activity also contributed to developmental regulation of LMN K_Ca density. A significant reduction in E11 K_Ca density was found after chronic in ovo treatment with the neuronal nicotinic antagonist mecamylamine or the GABA receptor agonist muscimol, agents that reduce activation of LMNs in ovo. Moreover, 3 d exposure to depolarizing concentrations of external K⁺ to LMNs cultured at E8 caused an increase in K_Ca expression. Conversely, tetrodotoxin caused a decrease in K_Ca expression in cultured E8 LMNs developing for 3 d in the presence of neurotrophic factors that promote neuronal survival in the absence of target tissues.

Key words: motoneuron; development; Ca²⁺-activated K⁺ channels; slowpoke; electrical activity; trophic factors

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Copyright © 2002 Society for Neuroscience  0270-6474/02/22173-09$05.00/0

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