Structural and functional response of toad urinary bladder to LiCl

AbstractStructural and functional response of toad urinary bladder to LiCl. The physiological and morphological response of toad urinary bladder was examined during mucosal exposure of LiCl both with and without vasopressin (VP). With 20 or 100 mU/ml of VP in the serosal bath there was a decrease in Jv between the first and second VP stimulation in LiCl-treated bladders (VP20, -14 ± 6%; VP100, -16 ± 5%) that was not different from that observed without LiCl (VP20, -8 ± 3%, P = NS). However, with 1 mU/ml of VP, a significant decrease in Jv was evident in LiCl-treated (-30 ± 10%) versus control sacs (+6 ± 8%; P < 0.02). At all VP concentrations tested, a significant decrease in SCC and PD was observed between the first stimulation without LiCl and the second stimulation with LiCl. Both osmotic (Pf) and diffusional water permeability (Pd) were increased significantly with 11 mM LiCl only, while neither basal nor VP-stimulated urea permeability (Pu) was affected. Morphological changes paralleled the physiological alterations induced by LiCl. These data demonstrate that LiCl interferes with the osmotic response of the toad bladder to low concentrations of VP, and increases both Pf and Pd while leaving Pu unaffected. These findings coupled with the cell swelling and intracellular vacuolization suggest the presence of a defect in transepithelial water movement somewhere beyond the apical membrane of the granular cell exposed to LiCl.Réponse structurelle et fonctionnelle de la vessie de crapaud au LiCl. La réponse physiologique et morphologique de la vessie de crapaud a été examinée pendant exposition de la muqueuse à du LiCl en présence ou en l'absence de vasopressine (VP). Pour 20 ou 100 mU/ml de VP dans le bain séreux, il y avait une diminution de Jv entre la première et la seconde stimulation par VP dans les vessies traitées par le LiCl (VP20, -14 ± 6%; VP100, -16 ± 5%), qui n'étaient pas différentes de celles observées sans LiCl (VP20, -8 ± 3%; P = NS). Cependant, avec 1 mU/ml de VP, une diminution significative de Jv était évidente dans les sacs traités au LiCl (-30 ± 10%) par rapport aux sacs contrôles (+6 ± 8%; P < 0,02). Pour toutes les concentrations de VP testées, une diminution significative du SCC et de PD a été observée entre la première stimulation sans LiCl, et la seconde stimulation avec LiCl. Les perméabilités osmotiques (Pf) et diffusionnelles (Pd) à l'eau étaient augmentées significativement avec 11 mM de LiCl seulement tandis que la perméabilité à l'urée basale ou stimulée par la VP (Pu) n'était pas affectée. Des modifications morphologiques allaient de pair avec les altérations physiologiques induites par le LiCl. Ces données démontrent que LiCl interfère avec la réponse osmotique de la vessie de crapaud pour de faibles concentrations de VP, augmente Pf et Pd, mais laisse Pu inchangé. Ces résultats, couplés avec le gonflement cellulaire et la vacuolisation intracellulaire suggèrent la présence d'un défaut du mouvement transépithélial d'eau quelque part au delà de la membrane apicale de la cellule granulaire exposée au LiCl

Metamorphosis in the Cirripede Crustacean Balanus amphitrite

Stalked and acorn barnacles (Cirripedia Thoracica) have a complex life cycle that includes a free-swimming nauplius larva, a cypris larva and a permanently attached sessile juvenile and adult barnacle. The barnacle cyprid is among the most highly specialized of marine invertebrate larvae and its settlement biology has been intensively studied. By contrast, surprisingly few papers have dealt with the critical series of metamorphic events from cementation of the cyprid to the substratum until the appearance of a suspension feeding juvenile. This metamorphosis is both ontogenetically complex and critical to the survival of the barnacle. Here we use video microscopy to present a timeline and description of morphological events from settled cyprid to juvenile barnacle in the model species Balanus amphitrite, representing an important step towards both a broader understanding of the settlement ecology of this species and a platform for studying the factors that control its metamorphosis. Metamorphosis in B. amphitrite involves a complex sequence of events: cementation, epidermis separation from the cypris cuticle, degeneration of cypris musculature, rotation of the thorax inside the mantle cavity, building of the juvenile musculature, contraction of antennular muscles, raising of the body, shedding of the cypris cuticle, shell plate and basis formation and, possibly, a further moult to become a suspension feeding barnacle. We compare these events with developmental information from other barnacle species and discuss them in the framework of barnacle settlement ecology

Aquaglyceroporin-null trypanosomes display glycerol transport defects and respiratory-inhibitor sensitivity

Aquaglyceroporins (AQPs) transport water and glycerol and play important roles in drug-uptake in pathogenic trypanosomatids. For example, AQP2 in the human-infectious African trypanosome, Trypanosoma brucei gambiense, is responsible for melarsoprol and pentamidine-uptake, and melarsoprol treatment-failure has been found to be due to AQP2-defects in these parasites. To further probe the roles of these transporters, we assembled a T. b. brucei strain lacking all three AQP-genes. Triple-null aqp1-2-3 T. b. brucei displayed only a very moderate growth defect in vitro, established infections in mice and recovered effectively from hypotonic-shock. The aqp1-2-3 trypanosomes did, however, display glycerol uptake and efflux defects. They failed to accumulate glycerol or to utilise glycerol as a carbon-source and displayed increased sensitivity to salicylhydroxamic acid (SHAM), octyl gallate or propyl gallate; these inhibitors of trypanosome alternative oxidase (TAO) can increase intracellular glycerol to toxic levels. Notably, disruption of AQP2 alone generated cells with glycerol transport defects. Consistent with these findings, AQP2-defective, melarsoprol-resistant clinical isolates were sensitive to the TAO inhibitors, SHAM, propyl gallate and ascofuranone, relative to melarsoprol-sensitive reference strains. We conclude that African trypanosome AQPs are dispensable for viability and osmoregulation but they make important contributions to drug-uptake, glycerol-transport and respiratory-inhibitor sensitivity. We also discuss how the AQP-dependent inverse sensitivity to melarsoprol and respiratory inhibitors described here might be exploited