PubMed · 4097425
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M Mlodzki. 1970. [Malabsorption syndrome].. https://pubmed.ncbi.nlm.nih.gov/4097425/
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The kinetics of ligand equilibration between the tubular and vesicular parts of the endosome are studied for ligands diffusing in the vesicle and in a narrow cylindrical tubule attached to it. The key quantity in our analysis is the fraction of ligands in the vesicle at time t, P(ves)(t). We derive an expression for the Laplace transform of P(ves)(t) as a function of the vesicle volume and the length and radius of the tubule as well as the ligand diffusion coefficients in the vesicle and in the tubule. This transform is used to find the average equilibration time as a function of the system parameters.
The epithelial lining of the lacrimal sac and the nasolacrimal duct consists of pseudo-stratified, columnar epithelia rich in goblet cells. Major secretory products of the epithelial cells are mucins together with TFF peptides. Expression and distribution of several mucins and TFF peptides in the human efferent tear ducts was investigated by means of reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. mRNAs for all the mucins investigated, MUC1, MUC2, MUC4, MUC5AC, MUC5B and MUC7, were detected in healthy human lacrimal sacs and nasolacrimal ducts. Both MUC5AC and MUC5B were detected in goblet cells forming intraepithelial mucous glands. MUC7 together with TFF3 occurred only in columnar epithelial cells of the efferent tear duct system. The mucin diversity of the efferent tear ducts could enhance tear transport and antimicrobial defense. The absence of some mucins in non-functioning although patent segments of the lacrimal passage, suggests that mucins ease tear flow through the efferent tear ducts because these conditions are associated with epiphora. Disorders in the balance of single mucins could be of importance with regard to dacryostenosis, dacryocystitis and dacryolith formation.
Time-resolved spectroscopy, absorption kinetic and electric signal measurement techniques were used to study the nitrate transporting photocycle of the pharaonis halorhodopsin. The spectral titration reveals two nitrate-binding constants, assigned to two independent binding sites. The high-affinity binding site (K(a) = 11 mM) contributes to the appearance of the nitrate transporting photocycle, whereas the low-affinity constant (having a K(a) of approximately 7 M) slows the last decay process in the photocycle. Although the spectra of the intermediates are not the same as those found in the chloride transporting photocycle, the sequence of the intermediates and the energy diagrams are similar. The differences in spectra and energy levels can be attributed to the difference in the size of the transported chloride or nitrate. Electric signal measurements show that a charge is transferred across the membrane during the photocycle, as expected. A new observation is an apparent release and rebinding of a small fraction of the retinal, inside the retinal pocket, during the photocycle. The release occurs during the N-to-O transition, whereas the rebinding happens in several seconds, well after the other steps of the photocycle are over.