The epithelial Na+ channel UNC-8 promotes an endocytic mechanism that recycles presynaptic components to new boutons in remodeling neurons

Circuit refinement involves the formation of new presynaptic boutons as others are dismantled. Nascent presynaptic sites can incorporate material from recently eliminated synapses, but the recycling mechanisms remain elusive. In early-stage C. elegans larvae, the presynaptic boutons of GABAergic DD neurons are removed and new outputs established at alternative sites. Here, we show that developmentally regulated expression of the epithelial Na+ channel (ENaC) UNC-8 in remodeling DD neurons promotes a Ca2+ and actin-dependent mechanism, involving activity-dependent bulk endocytosis (ADBE), that recycles presynaptic material for reassembly at nascent DD synapses. ADBE normally functions in highly active neurons to accelerate local recycling of synaptic vesicles. In contrast, we find that an ADBE-like mechanism results in the distal recycling of synaptic material from old to new synapses. Thus, our findings suggest that a native mechanism (ADBE) can be repurposed to dismantle presynaptic terminals for reassembly at new, distant locations.

Ion transport by sheep distal airways in a miniature chamber

Ion transport and the electric profile of distal airways of sheep lungs were studied in a miniature polypropylene chamber with a 1-mm aperture. Small airways with an inner diameter < 1 mm were isolated, opened longitudinally, and then mounted as a flat sheet onto the 1-mm aperture where it was glued and secured with an O-ring. Both sides of the tissue were bathed with identical physiological solutions at 37 degrees C and oxygenated. Pooled data from 27 distal airways showed an inner airway diameter of 854 +/- 22 (SE) microm and a transepithelial potential difference (PD) of 1.86 +/- 0.29 mV, lumen negative. Short-circuit current (I(sc)) was 25 +/- 3.5 microA/cm(2), tissue resistance was 96 +/- 14 Omega, and conductance was 15.2 +/- 1.7 mS/cm(2). At baseline, amiloride-sensitive Na transport accounted for 51% of I(sc) (change in I(sc) = 9.7 +/- 2.6 microA/cm(2); n = 8 airways), corresponding to 0.36 microeq. cm(-2). h(-1). Treatment with 0.1 mM bumetanide did not reduce the I(sc) (n = 5 airways). Exposure to 1 microM Ca ionophore A-23187 raised the I(sc) by 9 microA/cm(2) (47%; P < 0.03; n = 6 airways). The latter effect was blunted by bumetanide. Carbachol at 1 microM provoked a biphasic response, an initial rapid rise in I(sc) followed by a decline (n = 3 airways). There was no significant increase in PD or I(sc) in response to isoproterenol or dibutyryl cAMP. The data suggest that Na absorption constitutes at least 50% of baseline transport activity. Cl or other anion secretion such as HCO(3) appears to be present and could be stimulated by raising intracellular Ca.

Adaptation of the VOR in patients with low VOR gains

Six subjects with histories of vertigo and with vestibulo-ocular reflex (VOR) gains less than 0.5 were tested in an adaptation protocol. After initial VOR testing in the dark, the subjects had a computer-driven visual display system placed on their heads. The system had the capability for variation of visual image magnification. The magnification was set to be 5% greater than the subject's average VOR gain. Subjects then performed active head movements as they carried out a visual searching task looking for objects in a panoramic scene. After 6 minutes with each image, the magnification was increased by 3 to 5%. The process was repeated for a total of 5 images, for a total increase in magnification of approximately 20% over 30 minutes. The VOR gain was measured again. In 17 of 18 conditions tested, the VOR gain increased. The average increase was 16%. Significant increases in VOR gain occurred at 0.32 and 0.64 Hz. The VOR gain increase in these patients occurred in a visual environment that lowered VOR gain in normal subjects. These results suggest that the VOR has an adaptation mechanism tuned to correct for small changes in required gain. Further research is necessary to determine if this method can result in persistent VOR gain improvements and reduction in symptoms and disability in patients with vestibular disorders.

Divergence in patterns of invasion among subpopulations derived from a human carcinoma clone: roles of intercellular contacts and of cell-substratum adhesion

In tumor progression, populations of cancer cells with different patterns of growth and invasion arise within the same tissue and within individual neoplasms. We tested the hypothesis that, even in histologically undifferentiated carcinomas, such diversity may be influenced by differentiation-dependent adhesive mechanisms. We used as prototypes two cell lines that originated in the same clone of a poorly differentiated cervical carcinoma, but express strikingly different phenotypes. Cells of line C-4I express select characteristics of the spinous stage of stratified squamous epithelial differentiation while cells of line C-4II resemble basal cells. C-4I cells form rapidly expanding compact tumors in vivo and multilayered cohesive colonies in culture, while C-4II cells form slow-growing infiltrating tumors in vivo and dispersed, monolayered colonies in culture. In suspension culture which prevented any cell-substratum interactions, C-4I cells formed aggregates that were significantly larger and more compact than those formed by C-4II. Thus, greater intercellular adhesion between the 'spinous' C-4I cells contributed significantly to the phenotypic divergence of the lines. Upon disruption of intercellular adhesion with the glutamine analogue 6-diazo-4-oxo-norleucine (DON), C-4I cultures on plastic and in suspension assumed forms resembling C-4II. On plastic, single 'basal' C-4II cells adhered more rapidly and migrated more slowly than C-4I cells, in keeping with the capacity of C-4II, but not C-4I, to secrete fibronectin (FN) substrata. However, on exogenous FN matrices, migration and cell dispersion were accelerated in both lines. Both lines expressed similar integrin profiles. Thus, the lines had diverged in extracellular matrix production, but not in the receptors for extracellular matrix components. The properties of the C-4 lines mimic those of specific cell types in normal stratified squamous epithelia, where intercellular adhesion increases but FN secretion diminishes with progression from the basal to the spinous stage of differentiation. Our results demonstrate a direct influence of differentiation-associated adhesive mechanisms on growth patterns and suggest that similar mechanisms may be responsible for variations in invasiveness among neoplastic clonal subpopulations. An awareness of these correlations may help to interpret the modes of local invasion by poorly differentiated carcinomas in terms of specific, well-defined cell properties.