Structural analysis of toad oviductal mucosa in relation to jelly components secretion throughout the reproductive cycle

SummaryIn amphibians, the components of the jelly coats that surround the oocytes at the time of fertilization and coordinate gamete interaction are secreted by the oviduct. We analysed the histological variations in the mucosa of the oviductal pars convoluta (PC) of Rhinella arenarum during the reproductive cycle and its relationship with secretion. During the preovulatory period, the mucosa reaches a high degree of morphological and functional development, with a large number of epithelial (ESC) and glandular secretory cells (GSC) loaded with contents that are secreted into the oviductal lumen. During the ovulatory period, the secretory cells (SC) of both layers present maximum secretory activity through apocrinia and merocrinia. While the ESC located at the tips of the folds release their content directly in contact with the oocytes, the GSC secrete material from the bottom of the epithelial folds that, by interaction with the secretion of the ESC in the lateral faces, form a product with a certain degree of organization. Secretion is a continuous process with formation of coats of increasing complexity from the intermediate proximal zone (IPZ) to the pars convoluta (pc) itself, and the passage of the oocyte is a requisite for the organization of the jelly coats around the gamete.During the early postovulatory period, although there is a marked decrease in the number and volume of the SC, the ESC still release material into the oviductal lumen. In the late postovulatory period the morphological characteristics of the PC begin to recovery although there is no evidence of secretion.

Localization of PEPT1 and PEPT2 proton-coupled oligopeptide transporter mRNA and protein in rat kidney

To determine the renal localization of oligopeptide transporters, Northern blot analyses were performed and polyclonal antisera were generated against PEPT1 and PEPT2, the two cloned rat H+/peptide transporters. Under high-stringency conditions, a 3.0-kb mRNA transcript of rat PEPT1 was expressed primarily in superficial cortex, whereas a 3.5-kb mRNA transcript of PEPT2 was expressed primarily in deep cortex/outer stripe of outer medulla. PEPT1 antisera detected a specific band on immunoblots of renal and intestinal brush-border membrane vesicles (BBMV) with an apparent mobility of ∼90 kDa. PEPT2 antisera detected a specific broad band of ∼85 kDa in renal but not in intestinal BBMV. PEPT1 immunolocalization experiments showed detection of a brush border antigen in S1 segments of the proximal tubule and in the brush border of villi from all segments of the small intestine. In contrast, PEPT2 immunolocalization was primarily confined to the brush border of S3 segments of the proximal tubule. All other nephron segments in rat were negative for PEPT1 and PEPT2 staining. Overall, our results conclusively demonstrate that although PEPT1 is expressed in early regions of the proximal tubule (pars convoluta), PEPT2 is specific for the latter regions of proximal tubule (pars recta).

Induction of ornithine decarboxylase immunoreactivity in the male mouse kidney following testosterone treatment: an axial heterogeneity in the proximal tubule

ABSTRACT The effect of testosterone on the activity of ornithine decarboxylase (ODC), its protein level and immunocytochemical distribution were examined in the mouse kidney. Male BALB C mice at 8 weeks of age were used throughout. Fourteen hours before death, they received a subcutaneous injection of testosterone (1 mg/animal) or solvent to measure renal ODC activity or to detect the distribution of ODC immunoreactivity in the kidney. Renal ODC activity and the content of the enzyme were markedly increased after testosterone treatment. Histologically, few cells that were obviously immunoreactive to ODC were observed in the control animals and in the testosterone-treated animals a marked increase in ODC immunoreactivity was observed only in the cortex. ODC immunoreactive cells were located diffusely in the proximal tubule. In the pars recta, cells were stained weakly and homogeneously, while in the pars convoluta, the luminal surface of the cells showed stronger immunoreactivity. Moreover, many granule-like particles that were strongly ODC immunoreactive were observed inside the lumen of the pars convoluta. These results show that testosterone treatment induces an increase in ODC content in certain cells located in the proximal tubule of the cortex. Journal of Endocrinology (1993) 136, 85–89

Stepwise degradation of NT in pars convoluta and recta of rabbit proximal tubules: evidence of axial heterogeneity

Reabsorption and degradation of the neuropeptide neurotensin (NT) in rabbit proximal pars convoluta (PC) and pars recta (PR) nephron segments were characterized. Brush-border membrane vesicle fractions (PC or PR) were incubated with [3H]NT, and the extent and pattern of peptide hydrolysis were determined by reversed-phase high-pressure liquid chromatography (rHPLC). Furthermore, isolated rabbit PC and PR segments were perfused with [3H]NT, reabsorption of [3H]NT was quantified, and the collected perfusate was analyzed by HPLC. Metabolites were characterized. Finally, rabbit proximal tubules were microinfused in vivo with [3H]NT to follow the tubular uptake by electron microscope autoradiography. Degradation increased with time in both vesicle fractions. The main difference was an extensive cleavage of NT in PR, as revealed by a higher proportion of end metabolites. This was also visualized as a higher proportion of the large degradation product in rHPLC fraction 39 [NT-(1–11)] in PC as compared with PR after 30 min of incubation. The isolated perfused proximal tubular segments processed NT with large efficiency. PC segments processed 90% of the perfused amount, and PR processed 88%. Only 13% in PC and 10% in PR of the processed NT were found in the bath and the tubule. The main part of processed NT was in the collected perfusate, and rHLPC profiles revealed that NT-(1–11) was the only metabolite in both PC and PR. Electron microscope autoradiography demonstrated autoradiographic grains over invaginations and over the apical part of the proximal tubule cell in endocytic vesicles and vacuoles 10 min after microinfusion of [3H]NT.(ABSTRACT TRUNCATED AT 250 WORDS)

l-tryptophan uptake by segment-specific membrane vesicles from the proximal tubule of rabbit kidney

1. The mechanism of the renal transport of L-tryptophan by basolateral and luminal membrane vesicles prepared from either the pars convoluta or the pars recta of the rabbit proximal tubule was studied. The uptake of L-tryptophan by basolateral membrane vesicles from the pars convoluta was found to be an Na(+)-dependent transport event. The Na(+)-conditional influx of the amino acid was stimulated in the presence of an inwardly directed H+ gradient. Lowering the pH without an H+ gradient had no effect, indicating that L-tryptophan is co-transported with H+. 3. On the other hand, no transient accumulation of L-tryptophan was observed in the presence or absence of Na+ in basolateral membrane vesicles from the pars recta. 4. In luminal membrane vesicles from the pars recta, the transient Na(+)-dependent accumulation of L-tryptophan occurred via a dual transport system. In addition, an inwardly directed H+ gradient could drive the uphill transport of L-tryptophan into these vesicles in both the presence and the absence of an Na+ gradient. 5. By contrast, the uptake of L-tryptophan by luminal membrane vesicles from the pars convoluta was a strictly Na(+)-dependent and electrogenic transport process, mediated by a single transport component. 6. Investigation of the coupling ratio in luminal membrane vesicles suggested that 1 Na+:1 L-tryptophan are co-transported in the pars convoluta. In the pars recta, examination of the stoichiometry indicated that approx. 1 H+ and 2 Na+ (high affinity) or 1 Na+ (low affinity) are involved in the uptake of L-tryptophan.

Stoichiometric studies of β-alanine transporters in rabbit proximal tubule

The coupling ratio for the transport of beta-alanine and Na+, H+ and Cl- in luminal membrane vesicles isolated from proximal convoluted tubules (pars convoluta) and proximal straight tubules (pars recta) of rabbit kidney was examined. Indirect evidence indicates that 1 H+ and approx. 2 Na+, 1 Cl- (Na(+)-dependent, high-affinity) or 1 Na+ (Na(+)-dependent, low-affinity) are co-transported with beta-alanine in the pars convoluta. In pars recta, the two Na(+)-dependent transporters exhibited the same stoichiometric properties respectively as in pars convoluta.

Ca2+ and pH regulation of K+ channels in membrane vesicles of rabbit proximal tubule

The effect of Ca2+ and pH on the renal epithelial K+ channel was investigated by measuring the Ba2(+)-sensitive 86Rb+ fluxes in membrane vesicles from pars convoluta of rabbit proximal tubule. It was found that the presence of nanomolar concentrations of Ca2+ in the internal compartment (cytoplasmic) of the vesicles ([Ca2+]i) substantially lowered the channel-mediated flux. Ba2(+)-sensitive 86Rb+ uptake was completely blocked by 10 microM [Ca2+]i. This inhibitory effect of Ca2+ was strongly dependent on pH. Thus 0.1 microM [Ca2+]i produced a maximal inhibition of 86Rb+ uptake at pH greater than 7.4 but had no effect at pH less than 7.0. The tracer fluxes measured in the absence of Ca2+ were pH independent over this range. The data are compatible with the model that Ca2+ blocks K+ channels by binding to a site composed of one or several deprotonated groups. The protonation of any one of these groups prevents Ca2+ from binding to this site but does not by itself block transport.