1. Starburst amacrine cells were studied using whole cell patch recording. Displaced starburst cells were labeled in rabbit retinas by intraocular injection of 4,6-diamidino-2-phenylindole. The retinas were isolated and maintained in vitro. The inner limiting membrane and Müller cell endfeet were removed mechanically from small areas above the starburst cell bodies, allowing an unimpeded approach under visual control to the cells. A total of 104 cells was studied. 2. In voltage-clamp recordings, the cells responded to light with slow, graded inward and outward currents on which were superimposed smaller, rapid inward currents. The rapid inward currents appeared to be postsynaptic currents. 3. The receptive fields of the cells were mapped using small spots. They had an on-center, off-surround organization. Visualizing the dendrites by including Lucifer yellow in the patch pipette showed that the receptive fields' centers closely approximated the dendritic spread of the neurons. 4. The cells' responses to movement were tested with smooth movements or with two-spot apparent motion. No directional preference was seen for spots swept across the whole receptive field, for centrifugal movements, or for centripetal movements. 5. Bath-applied tetrodotoxin (TTX) or intracellularly applied lidocaine N-ethyl bromide (QX-314) had no effect on any component of the spontaneous or light-evoked activity. Depolarization of the cell bodies by injected current showed evidence of active conductances, but they were unaffected by TTX or QX-314. 6. 6-Cyano-7-nitroquionxyline-2,3-dione eliminated the small rapid currents, indicating that they depend on alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid/kainate glutamate receptors. 7. Because it is unlikely that we voltage clamped the distalmost dendrites of these wide-field cells, uncertainties remain about rapid electrical events occurring in the dendrites. From a functional point of view, though, the fact that slow responses to distal photic stimulation were recorded at the soma suggests that the starburst cells could in principle integrate inputs across fairly substantial fractions of their total dendritic arbors. The extent to which this actually occurs remains to be learned.

Many bacteria move using a complex, self-assembling nanomachine, the bacterial flagellum. Biosynthesis of the flagellum depends on a flagellar-specific type III secretion system (T3SS), a protein export machine homologous to the export machinery of the virulence-associated injectisome. Six cytoplasmic (FliH/I/J/G/M/N) and seven integral-membrane proteins (FlhA/B FliF/O/P/Q/R) form the flagellar basal body and are involved in the transport of flagellar building blocks across the inner membrane in a proton motive force-dependent manner. However, how the large, multi-component transmembrane export gate complex assembles in a coordinated manner remains enigmatic. Specific for most flagellar T3SSs is the presence of FliO, a small bitopic membrane protein with a large cytoplasmic domain. The function of FliO is unknown, but homologs of FliO are found in >80% of all flagellated bacteria. Here, we demonstrate that FliO protects FliP from proteolytic degradation and promotes the formation of a stable FliP–FliR complex required for the assembly of a functional core export apparatus. We further reveal the subcellular localization of FliO by super-resolution microscopy and show that FliO is not part of the assembled flagellar basal body. In summary, our results suggest that FliO functions as a novel, flagellar T3SS-specific chaperone, which facilitates quality control and productive assembly of the core T3SS export machinery.

The giant non-fimbrial adhesin SiiE of Salmonella enterica mediates the first contact to the apical site of epithelial cells and enables subsequent invasion. SiiE is a 595 kDa protein composed of 53 repetitive bacterial immunoglobulin (BIg) domains and the only known substrate of the SPI4-encoded type 1 secretion system (T1SS). The crystal structure of BIg50-52 of SiiE revealed two distinct Ca2+-binding sites per BIg domain formed by conserved aspartate or glutamate residues. In a mutational analysis Ca2+-binding sites were disrupted by aspartate to serine exchange at various positions in the BIg domains of SiiE. Amounts of secreted SiiE diminish with a decreasing number of intact Ca2+-binding sites. BIg domains of SiiE contain distinct Ca2+-binding sites, with type I sites being similar to other T1SS-secreted proteins and type II sites newly identified in SiiE. We functionally and structurally dissected the roles of type I and type II Ca2+-binding sites in SiiE, as well as the importance of Ca2+-binding sites in various positions of SiiE. Type I Ca2+-binding sites were critical for efficient secretion of SiiE and a decreasing number of type I sites correlated with reduced secretion. Type II sites were less important for secretion, stability and surface expression of SiiE, however integrity of type II sites in the C-terminal portion was required for the function of SiiE in mediating adhesion and invasion.

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