Activity-dependent release of tissue plasminogen activator from the dendritic spines of hippocampal neurons revealed by live-cell imaging

J Neurobiol. 2006 May;66(6):564-77. doi: 10.1002/neu.20250.


Tissue plasminogen activator (tPA) has been implicated in a variety of important cellular functions, including learning-related synaptic plasticity and potentiating N-methyl-D-aspartate (NMDA) receptor-dependent signaling. These findings suggest that tPA may localize to, and undergo activity-dependent secretion from, synapses; however, conclusive data supporting these hypotheses have remained elusive. To elucidate these issues, we studied the distribution, dynamics, and depolarization-induced secretion of tPA in hippocampal neurons, using fluorescent chimeras of tPA. We found that tPA resides in dense-core granules (DCGs) that traffic to postsynaptic dendritic spines and that can remain in spines for extended periods. We also found that depolarization induced by high potassium levels elicits a slow, partial exocytotic release of tPA from DCGs in spines that is dependent on extracellular Ca(+2) concentrations. This slow, partial release demonstrates that exocytosis occurs via a mechanism, such as fuse-pinch-linger, that allows partial release and reuse of DCG cargo and suggests a mechanism that hippocampal neurons may rely upon to avoid depleting tPA at active synapses. Our results also demonstrate release of tPA at a site that facilitates interaction with NMDA-type glutamate receptors, and they provide direct confirmation of fundamental hypotheses about tPA localization and release that bear on its neuromodulatory functions, for example, in learning and memory.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Bacterial Proteins
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology
  • Cells, Cultured
  • Dendritic Spines / metabolism*
  • Exocytosis / drug effects
  • Exocytosis / physiology
  • Hippocampus / metabolism*
  • Luminescent Proteins
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Memory / physiology
  • Microscopy, Fluorescence / methods
  • Microscopy, Video / methods
  • Mutant Chimeric Proteins / metabolism
  • Potassium / metabolism
  • Potassium / pharmacology
  • Protein Transport / physiology
  • Pyramidal Cells / metabolism*
  • Rats
  • Receptors, N-Methyl-D-Aspartate / metabolism
  • Secretory Vesicles / metabolism
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*
  • Time Factors
  • Tissue Plasminogen Activator / genetics
  • Tissue Plasminogen Activator / metabolism*


  • Bacterial Proteins
  • Luminescent Proteins
  • Mutant Chimeric Proteins
  • Receptors, N-Methyl-D-Aspartate
  • yellow fluorescent protein, Bacteria
  • Tissue Plasminogen Activator
  • Potassium