Syntaxin 3B is essential for the exocytosis of synaptic vesicles in ribbon synapses of the retina.

Ribbon synapses of the vertebrate retina are specialized synapses that release neurotransmitter by synaptic vesicle exocytosis in a manner that is proportional to the level of depolarization of the cell. This release property is different from conventional neurons, in which the release of neurotransmitter occurs as a short-lived burst triggered by an action potential. Synaptic vesicle exocytosis is a calcium regulated process that is dependent on a set of interacting synaptic proteins that form the so-called SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) complex. Syntaxin 3B has been identified as a specialized SNARE molecule in ribbon synapses of the rodent retina. However, the best physiologically-characterized neuron that forms ribbon-style synapses is the rod-dominant or Mb1 bipolar cell of the goldfish retina. We report here the molecular characterization of syntaxin 3B from the goldfish retina. Using a combination of reverse transcription (RT) polymerase chain reaction (PCR) and immunostaining with a specific antibody, we show that syntaxin 3B is highly enriched in the plasma membrane of bipolar cell synaptic terminals of the goldfish retina. Using membrane capacitance measurements we demonstrate that a peptide derived from goldfish syntaxin 3B inhibits synaptic vesicle exocytosis. These experiments demonstrate that syntaxin 3B is an important factor for synaptic vesicle exocytosis in ribbon synapses of the vertebrate retina.

The inhibition of lipid transfer protein by negatively charged liposomes modifies the therapeutic index of amphotericin B

We have shown that liposomal amphotericin B (L-AmpB) decreased renal toxicity and maintains the antifungal activity of amphotericin B (AmpB). We have also observed that L-AmpB is predominantly associated with high density lipoproteins (HDL) as compared to Fungizone (AmpB + deoxycholate). The present experiments were designed to assess the biological relevance of transferring AmpB to HDL. We observed that AmpB was less toxic to kidney cells when associated with HDL, however AmpB toxicity was maintained when associated with LDL. To further understand how HDL-associated AmpB reduces renal cell toxicity the presence of HDL and LDL receptors in this cell line was determined. We observed that these cells expressed high and low affinity LDL receptors, but only low affinity HDL receptors. The reduced renal cell toxicity of HDL-associated AmpB may be due to its lack of interaction with renal cells because of the absence of HDL receptors. Since AmpB interacts with cholesteryl esters whose transfer among lipoproteins is regulated by Lipid transfer Protein (LTP), the role of LTP on the distribution of AmpB to HDL and LDL was next examined. We found that negatively charged liposomes significantly reduced LTP-mediated transfer of CE between HDL and LDL, independent of the presence of AmpB, while Fungizone only significantly inhibited CE transfer at one concentration tested (20$\mu$g/ml). Therefore, we believe that the decreased renal toxicity of L-AmpB is related to its predominant distribution to HDL which is regulated by the inhibition of LTP activity. ^