Tomosyn inhibits priming of large dense-core vesicles in a calcium-dependent manner.
Neurotransmitter release is a multistep process that is coordinated by a large number of synaptic proteins and depends on proper protein-protein interactions. Using morphological, capacitance, and amperometric measurements, we investigated the effect of tomosyn, a Syntaxin-binding protein, on the different kinetic components of exocytosis in adrenal chromaffin cells. Overexpression of tomosyn decreased the release probability and led to a 50% reduction in the number of fusion-competent vesicles. The number of docked vesicles and the fusion kinetics of single vesicles were not altered suggesting that tomosyn inhibits the priming step. Interestingly, this inhibition is partially relieved at elevated calcium concentration. Calcium ramp experiments supported the latter finding and indicated that the reduction in secretion is caused by a shift in the calcium-dependence of release. These results indicate that secretion is not entirely blocked but occurs at higher calcium concentrations. We suggest that tomosyn inhibits the priming step and impairs the efficiency of vesicle pool refilling in a calcium-dependent manner.
Department of Neurobiochemistry, Life Sciences Institute, Tel Aviv University, Tel Aviv 69978, Israel.
Ofer
O
Yizhar
Ulf
U
Matti
Rely
R
Melamed
Yamit
Y
Hagalili
Dieter
D
Bruns
Jens
J
Rettig
Uri
U
Ashery
D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology; D019439:Chromaffin Cells / Q000502:physiology*; D004594:Electrophysiology / Q000379:methods; D005089:Exocytosis / Q000502:physiology*; D015723:Gene Library; D007700:Kinetics; D009419:Nerve Tissue Proteins / Q000502:physiology*; D010782:Photolysis; D010957:Plasmids; D016133:Polymerase Chain Reaction; D050683:R-SNARE Proteins; D051381:Rats; D022142:Secretory Vesicles / Q000502:physiology*; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; C484769:Stxbp5 protein, rat; D033921:Vesicular Transport Proteins; D002118:Calcium