Direct modulation of the secretory machinery underlies PKA-dependent synaptic facilitation in hippocampal neurons.
Activation of protein kinase A (PKA) is known to facilitate synaptic transmission. Using synapses established by hippocampal neurons in culture, we show that dialysis of PKA inhibitors in the presynaptic neuron blocks synaptic facilitation produced by the adenylyl cyclase activator forskolin, demonstrating a presynaptic locus of action. Using ruthenium red, a tool that is known to stimulate exocytosis independently of Ca2+ influx, but in a manner sensitive to tetanus toxin, we find that the secretory process is directly up-regulated under conditions where the number of functional terminals remains unchanged, as revealed by imaging of FM1-43, a vital indicator of synaptic vesicle endocytosis. Taken together with our ultrastructural analysis that suggests no enhancement of docking, our data indicate that PKA causes synaptic facilitation by directly elevating the probability of exocytosis of individual vesicles in response to an invariant Ca2+ signal.
Department of Zoology and Genetics, Iowa State University, Ames 50011, USA.
L E
LE
Trudeau
D G
DG
Emery
P G
PG
Haydon
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004705:Endocytosis; D005071:Evoked Potentials / Q000502:physiology*; D005089:Exocytosis; D005456:Fluorescent Dyes; D006624:Hippocampus / Q000502:physiology*; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D008959:Models, Neurological; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000502:physiology; D013744:Tetanus Toxin / Q000494:pharmacology
D015220:Calcium Channels; C073804:FM1 43; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D013744:Tetanus Toxin; D012430:Ruthenium Red; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D002118:Calcium