BRAIN-DERIVED NEUROTROPHIC FACTOR INHIBITS NEUROMUSCULAR JUNCTION MATURATION MEDIATED BY INTRACELLULAR Ca2+ AND Ca2+/CALMODULIN-DEPENDENT KINASE

Introduction: Brain-derived neurotrophic factor (BDNF) inhibits neuromuscular junction (NMJ) maturation. In this study we investigated the underlying molecular mechanisms of this process. Methods: We used a patch-clamp technique to measure spontaneous synaptic currents (SSCs) from innervated muscle cells in Xenopus nerve-muscle cocultures. Results: In the presence of Ca2+/calmodulin-dependent kinase (CaMK) inhibitor KN93, SSC amplitude (226.3 +/- 26.5 pA), frequency (30.9 +/- 10.1 events/min), and percentage of bell-shaped amplitude distributions (47.1%) were reversed to control levels (286.7 +/- 48.2 pA, 26.2 +/- 5.8 events/min, and 47.1%, respectively). Depletion of intracellular Ca2+ by BAPTA-AM or thapsigargin had similar reversal effects to KN93. In addition, cotreatment with both 2-APB (IP3 receptor inhibitor) and TMB-8 (ryanodine receptor inhibitor) also reversed the inhibitory effects of BDNF, as shown by the physiological parameters. Conclusions: CaMK mediates the inhibitory effects of BDNF on NMJ maturation. Ca2+ released from intracellular stores through either IP3 receptors or ryanodine receptors regulates neurotrophic actions on NMJ maturation.