Small dense-cored vesicles are depleted of the classical synaptic vesicle membrane proteins synaptobrevin, synaptotagmin and Rab3

To verify the association of vesicular docking/fusion proteins to small dense-cored vesicles, we further purified a small dense-cored vesicle population from rat vas deferens and searched for three components of the vesicular docking/fusion machinery known to act on target receptors at the plasma membrane: synaptobrevin (p18), synaptotagmin (p65) and the small GTPase Rab3. Further purification of small dense-cored vesicles actually resulted in a depletion of these proteins, arguing against a direct participation of small dense-cored vesicles in the exocytotic process. This finding points to a functional difference between small dense-cored vesicles and either large dense-cored or small clear synaptic vesicles.