Ion transport across the early chick embryo: I. Electrical measurements, ionic fluxes and regional heterogeneity

Routine experimental system for defining conditions used in photodynamic therapy and fluorescence photodetection of (non-) neoplastic epithelia

A common method to induce enhanced short-term endogenous porphyrin synthesis and accumulation in cell is the topical, systemic application of 5-aminolevulinic acid or one of its derivatives. This circumvents the intravenous administration of photosensitizers normally used for photodynamic therapy (PDT) of fluorescence photodetection. However, in the majority of potential medical indications, optimal conditions with respect to the porphyrin precursor or its pharmaceutical formulation have not yet been found. Due to ethical restrictions and animal right directives, the number of available test objects is limited. Hence, definition and use of nonanimal test methods are needed. Tissue and organ cultures are a promising approach in replacing cost intensive animal models in early stages of drug development. In this paper, we present a tissue culture, which can among others be used routinely to answer specific questions emerging in the field of photodynamic therapy and fluorescence photodetection. This technique uses mucosae excised from sheep paranasal sinuses or pig bladder, which is cultured under controlled conditions. It allows quasiquantitative testing of different protoporphyrin IX precursors with respect to dose-response curves and pharmacokinetics, as well as the evaluation of different incubation conditions and/or different drug formulations. Furthermore, this approach, when combined with the use of electron microscopy and fluorescence-based methods, can be used to quantitatively determine the therapeutic outcome following protoporphyrin IX-mediated PDT.

In vitro engineering of human stratified urothelium: analysis of its morphology and function

PURPOSE

Gastric or intestinal patches, commonly used for reconstructive cystoplasty, may induce severe metabolic complications. The use of bladder tissues reconstructed in vitro could avoid these complications. We compared cellular differentiation and permeability characteristics of human native with in vitro cultured stratified urothelium.

MATERIALS AND METHODS

Human stratified urothelium was induced in vitro. Morphology was studied with light and electron microscopy and expression of key cellular proteins was assessed using immunohistochemistry. Permeability coefficients were determined by measuring water, urea, ammonia and proton fluxes across the urothelium.

RESULTS

As in native urothelium the stratified urothelial construct consisted of basal membrane and basal, intermediate and superficial cell layers. The apical membrane of superficial cells formed villi and glycocalices, and tight junctions and desmosomes were developed. Immunohistochemistry showed similarities and differences in the expression of cytokeratins, integrin and cellular adhesion proteins. In the cultured urothelium cytokeratin 20 and integrin subunits alpha6 and beta4 were absent, and symplekin was expressed diffusely in all layers. Uroplakins were clearly expressed in the superficial umbrella cells of the urothelial constructs, however, they were also present in intermediate and basal cells. Symplekin and uroplakins were expressed only in the superficial cells of native bladder tissue. The urothelial constructs showed excellent viability, and functionally their permeabilities for water, urea and ammonia were no different from those measured in native human urothelium. Proton permeability was even lower in the constructs compared to that of native urothelium.

CONCLUSIONS

Although the in vitro cultured human stratified urothelium did not show complete terminal differentiation of its superficial cells, it retained the same barrier characteristics against the principal urine components. These results indicate that such in vitro cultured urothelium, after being grown on a compliant degradable support or in coculture with smooth muscle cells, is suitable for reconstructive cystoplasty.

Ion transport across the early chick embryo: II. Characterization and pH sensitivity of the transembryonic short-circuit current

The ectoderm of the one-day chick embryo generates dorsoventrally oriented short-circuit current (Isc) entirely dependent on extracellular sodium. At the dorsal cell membrane, the Isc was modified reversibly and in a concentration-dependent manner by: amiloride (60% decrease at 1 mM, with 2 apparent IC50S: 0.13 and 48 microM), phlorizin (0.1 mM) or removal of glucose (30% decrease, additive to that of amiloride), SITS (1 mM, 13% decrease). Acidification of alkalinization of the dorsal (but not ventral) superfusate produced, respectively, decrease or increase of Isc with a pH50 of 7.64. Ba2+ (0.1-1 mM) from either side of the ectoderm decreased the Isc by 30%. Anthracene-9-carboxylic acid, furosemide and inducers of cAMP had no effect on electrophysiological properties of the blastoderm. The chick ectoderm is therefore a highly polarized epithelium containing, at the dorsal membrane, the high and low affinity amiloride-sensitive Na+ channels, Na(+)-glucose cotransporter, K+ channels and pH sensitivity, and, at the ventral membrane, the Na+, K(+)-ATPase and K+ channels. The Na+ transport reacts to pH, but lacks the cAMP regulatory system, well known in many epithelia. The active Na+ transport drives glucose and fluid into the intraembryonic space, across and around the blastoderm which, in the absence of blood circulation, could secure renewal of extracellular fluid and disposal of wastes and thus maintain the cell homeostasis.