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W M DeBello

Publications and source records attributed to W M DeBello.

8 recordsLinked to original sources
PubMed1998

A neuronal Sec1 homolog regulates neurotransmitter release at the squid giant synapse.

Sec1-related proteins are essential for membrane fusion at distinct stages of the constitutive and regulated secretory pathways in eukaryotic cells. Studies of neuronal isoforms of the Sec1 protein family have yielded evidence for both positive and negative regulatory functions of these proteins in neurotransmitter release. Here, we have identified a squid neuronal homolog (s-Sec1) of Sec1 proteins and examined its function in neurotransmitter release at the squid giant synapse. Microinjection of s-Sec1 into the presynaptic terminal of the giant synapse inhibited evoked neurotransmitter release, but this effect was prevented by coinjecting the cytoplasmic domain of squid syntaxin (s-syntaxin), one of the binding partners of s-Sec1. A 24 amino acid peptide fragment of s-Sec1, which inhibited the binding of s-Sec1 to s-syntaxin in vitro, completely blocked release, suggesting an essential function of the s-Sec1/s-syntaxin interaction in transmitter release. Electron microscopy showed that injection of s-Sec1 did not change the spatial distribution of synaptic vesicles at presynaptic release sites ("active zones"), whereas the inhibitory peptide increased the number of docked vesicles. These distinct morphological effects lead us to conclude that Sec1 proteins function at different stages of synaptic vesicle exocytosis, and that an interaction of s-Sec1 with syntaxin-at a stage blocked by the peptide-is necessary for docked vesicles to fuse.

Animals↗
PubMed1998

Regulation of neurotransmitter release kinetics by NSF.

NSF (N-ethylmaleimide-sensitive factor) is an adenosine triphosphatase (ATPase) that contributes to a protein complex essential for membrane fusion. The synaptic function of this protein was investigated by injecting, into the giant presynaptic terminal of squid, peptides that inhibit the ATPase activity of NSF stimulated by the soluble NSF attachment protein (SNAP). These peptides reduced the amount and slowed the kinetics of neurotransmitter release as a result of actions that required vesicle turnover and occurred at a step subsequent to vesicle docking. These results define NSF as an essential participant in synaptic vesicle exocytosis that regulates the kinetics of neurotransmitter release and, thereby, the integrative properties of synapses.

Adenosine Triphosphatases↗
PubMed1996

Exocytosis: proteins and perturbations.

Exocytosis is the primary means of cellular secretion. Because exocytosis involves fusion between the plasma membrane and the membrane of secretory vesicles, it is likely that proteins on these two membranes, as well as additional proteins in cellular cytoplasm, mediate exocytosis. Although we know much about the proteins of secretory cells, we still have much to learn about how these proteins participate in exocytosis; in no case has an unambiguous exocytotic function been assigned to any of these proteins. To identify the roles of proteins in exocytosis it is necessary to perturb protein function in living secretory cells. We review a number of perturbation strategies and summarize what this approach has taught us about the functional roles of proteins in exocytosis, concluding with a molecular model of protein dynamics during exocytosis.

Animals↗
PubMed1995

SNAP-mediated protein-protein interactions essential for neurotransmitter release.

The constitutive fusion of transport vesicles with intracellular membranes requires soluble proteins called SNAPs. Certain presynaptic proteins implicated in synaptic vesicle exocytosis also bind SNAPs, suggesting that SNAPs participate in the calcium-regulated membrane fusion events mediating neurotransmitter release. Here we show that injection of recombinant SNAPs into the giant synapse of squid enhances transmitter release. Conversely, injection of peptides designed to mimic the sites at which SNAP interacts with its binding partners inhibits transmitter release downstream of synaptic vesicle docking. A SNAP-dependent protein complex must therefore mediate transmitter release, showing that transmitter release shares a common molecular mechanism with constitutive membrane fusion.

Amino Acid Sequence↗
PubMed1994

Molecular pathways for presynaptic calcium signaling.

The results presented in this article describe two distinct, Ca-regulated molecular pathways in presynaptic terminals and implicate these two pathways in differentially mediating neurotransmitter secretion and PTP. Our current view of the Ca-dependent triggering of secretion and PTP is shown in Fig. 9. According to this scheme, differential activation of these two pathways is achieved by a combination of diffusion-based dilution of Ca that enters the terminal through voltage-gated Ca channels and by coupling these pathways to Ca receptors with different affinities for Ca ions. A simple way to achieve these conditions is to position these two receptors at different distances from the Ca channels, as shown in Fig. 2. Given that Ca ions are involved in activating many different presynaptic processes (Fig. 1), we propose that closer scrutiny of the molecular physiology of nerve terminals will reveal a wide variety of Ca-activated pathways responsible for producing these diverse processes.

Amino Acid Sequence↗
PubMed1993

Inhibition of neurotransmitter release by C2-domain peptides implicates synaptotagmin in exocytosis.

Neurotransmitter release is triggered by Ca2+ ions binding to an unknown Ca2+ receptor within presynaptic terminals. Synaptotagmin, a Ca2(+)-binding protein of synaptic and other secretory vesicles, has been proposed to mediate vesicle-plasma membrane interactions during neurotransmitter release. Here we test this hypothesis using the giant synapse of the squid Loligo pealei, which because of its unusually large size and well established physiology is uniquely suited for dissecting presynaptic events. We find that injection of peptides from the C2 domains of synaptotagmin into squid giant presynaptic terminals rapidly and reversibly inhibits neurotransmitter release. Our data are consistent with these peptides competitively blocking release after synaptic vesicle docking and indicate that Ca2+ probably initiates neurotransmitter release by regulating the interaction of synaptotagmin with an acceptor protein.

Amino Acid Sequence↗