Regulation of acetylcholine release by extracellular matrix proteins at developing motoneurons in Xenopus cell cultures

Integrins mediate cell-extracellular matrix connections and are particularl y important during neuronal development. We here investigated the regulator y role of extracellular matrix (ECM) proteins on the synaptic transmission at developing motoneurons. Synaptic currents were recorded from innervated myocytes of 1-day-old Xenopus cultures by whole-cell recordings. Soluble fi bronectin and laminin had no significant effect on the frequency of spontan eous synaptic currents (SSCs) by themselves and markedly increased SSC freq uency in the presence of low concentration of protein kinase C (PKC) activa tors. Pretreatment with Gly-Arg-Gly-Asp-Ser peptide inhibited the SSC incre asing action of 12-o-tetradecanoylphorbol-13-acetate (TPA, 0.5 muM) plus fi bronectin, but not that of TPA plus laminin. Genistein but not cytochalasin D inhibited the SSC increasing action of TPA plus fibronectin or laminin. High concentration of TPA (5 muM) markedly increased the SSC frequency by i tself and occluded the SSC increasing action of fibronectin. Very low conce ntration of TPA (0.05 muM) markedly enhanced the SSC frequency when the cel ls were plated onto fibronectin- or laminin-coated substratum for 1 day. Th e SSC frequency increased markedly right after a train stimulation, which w as defined as post-train potentiation (PTrP), when the cultures were plated onto fibronectin substratum and chronically treated with brain-derived neu rotrophic factor (BDNF). The PTrP phenomenon is not observed upon chronic t reatment with neurotrophin-3, glial cell line-derived neurotrophic factor, or ciliary neurotrophic factor. Our results suggest that the activation of PKC and tyrosine kinase but not actin reorganization plays a role in the SS C potentiating action of fibronectin. BDNF exerts synergistic effects in in creasing synaptic transmission in neurons grown on fibronectin substratum. ECMs in concert with neurotrophic factor may play a role in regulating syna ptic function at developing motoneurons. (C) 2000 Wiley-Liss, Inc.