This Article Full Text Full Text (PDF) Supplemental All Versions of this Article: biophysj.106.080978v1 90/6/L45    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Sturman, D. A. Articles by Levitan, E. S. Search for Related Content PubMed PubMed Citation Articles by Sturman, D. A. Articles by Levitan, E. S.

Nearly Neutral Secretory Vesicles in Drosophila Nerve Terminals

David A. Sturman ^*, Dinara Shakiryanova ^*, Randall S. Hewes , David L. Deitcher  and Edwin S. Levitan ^*

^* Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania; Department of Zoology, University of Oklahoma, Norman, Oklahoma; and Department of Neurobiology and Behavior, Cornell University, Ithaca, New York

Correspondence: Address reprint requests and inquiries to Edwin Levitan, E-mail: levitan{at}server.pharm.pitt.edu.

The acidity of mammalian secretory vesicles drives concentration and processing of their contents. Here, pH-sensitive green fluorescent protein (GFP) variants show that the 30-fold (H⁺) difference between secretory vesicles (pH 5.7) and the cytoplasm (pH = 7.2) in mammalian cells is not present in peptidergic and small synaptic vesicles of the Drosophila neuromuscular junction. First, we find that fluorescence from Topaz-tagged atrial natriuretic factor, a peptidergic vesicle pH indicator, is only modestly affected by collapsing the H⁺ gradient in type III synaptic boutons. Quantitation shows that peptidergic vesicles are nearly neutral (pH = 6.74 ± 0.05), even when temperature is elevated. Furthermore, small synaptic vesicles in glutamatergic synaptic boutons, studied with synaptophluorin, are as alkaline as peptidergic vesicles. Finally, yellow fluorescent protein measurements show that cytoplasmic pH is only slightly different than in mammals (pH = 7.4). Thus, the marked acidity of mammalian secretory vesicles is not conserved in evolution, and a modest vesicular H⁺ gradient is sufficient for supporting neurotransmission.