BDNF induces calcium elevations associated with IBDNF, a nonselective cationic current mediated by TRPC channels

Abstract

Brain-derived neurotrophic factor (BDNF) has potent actions on hippocampal neurons, but the mechanisms that initiate its effects are poorly understood. We report here that localized BDNF application to apical dendrites of CA1 pyramidal neurons evoked transient elevations in intracellular Ca(2+) concentration, which are independent of membrane depolarization and activation of N-methyl-d-aspartate receptors (NMDAR). These Ca(2+) signals were always associated with I(BDNF), a slow and sustained nonselective cationic current mediated by transient receptor potential canonical (TRPC3) channels. BDNF-induced Ca(2+) elevations required functional Trk and inositol-tris-phosphate (IP(3)) receptors, full intracellular Ca(2+) stores as well as extracellular Ca(2+), suggesting the involvement of TRPC channels. Indeed, the TRPC channel inhibitor SKF-96365 prevented BDNF-induced Ca(2+) elevations and the associated I(BDNF). Thus TRPC channels emerge as novel mediators of BDNF-induced intracellular Ca(2+) elevations associated with sustained cationic membrane currents in hippocampal pyramidal neurons.

FIG. 1

Brain-derived neurotrophic factor (BDNF) induces intracellular Ca²⁺ elevations that precede and are simultaneous with I_BDNF activation. A: representative example of BDNF-evoked Ca²⁺ signals in the presence of TTX, Cd²⁺ and d,l-2-amino-5-phosphonovaleric acid (d,l-APV). These Ca²⁺ elevations included a transient and localized dendritic signal during BDNF application (—) and a secondary widespread elevation associated with I_BDNF. The initial Ca²⁺ transient (*) is shown in B at an expanded time scale. B: expanded view of the initial Ca²⁺ elevation that preceded I_BDNF. Here and in the other figures, the fluorescence images (360 nm excitation) show the color-coded regions of interest (ROIs) plotted with the simultaneously recorded membrane currents.

FIG. 2

BDNF-induced Ca²⁺ signals require functional Trk and IP₃ receptors. A: BDNF-evoked Ca²⁺ signals and I_BDNF are sensitive to the Trk inhibitor k-252a (200 nM). B: The IP₃R inhibitor xestospongin-C (1 µM intracellular) blocked BDNF-evoked Ca²⁺ signals and I_BDNF.

FIG. 3

BDNF-induced Ca²⁺ signals require full intracellular Ca²⁺ stores, Ca²⁺ influx from the extracellular space, and activation of TRPC channels. A: depletion of intracellular Ca²⁺ stores with thapsigargin (1 µM) abolished BDNF Ca²⁺ responses and I_BDNF. B: applying BDNF in the absence of extracellular Ca²⁺ failed to evoke Ca²⁺ elevations and significantly reduced I_BDNF. C: The TRPC inhibitor SKF-96365 (30 µM) prevented Ca²⁺ signals and I_BDNF.