PubMed · 2575206
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
K Sandvig, S Olsnes, O W Petersen, B Van Deurs. 1989. Control of coated-pit function by cytoplasmic pH.. https://doi.org/10.1016/s0091-679x(08)61181-4
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
In this paper we formulate a mathematical model for the receptor mediated endocytotic cycle under the influence of diffusion, radial convection, and generalized receptor reinsertion. The steady state radial concentration function of unbound receptors admits an explicit representation. This can be expressed as a functional of the insertion rate, the diffusion coefficient, and the flow strength. Using the referred functional we study the influence of the aforementioned mechanisms on the surface aggregation pattern of low density lipoprotein (LDL) receptors near coated pits. We perform that analysis on both a theoretical level and by means of simulated receptor aggregation patterns obtained by computer graphics techniques. We conclude that radially convective diffusion in combination with suitable characterizations of the insertion mode are consistent with reported cell surface aggregation patterns.
We consider a linear receptor reinsertion step in our kinetic model of the primary steps occurring in receptor-mediated endocytosis. In contrast with our previous zeroth order receptor reinsertion assumption, here we consider a first order process, and we study the effect of receptor diffusion on the trapping rate constant (k+) and the radial distribution of receptors around coated pits (grp). Using experimental data for low density lipoproteins (LDL) receptors on fibroblast cells, we find that the trapping of receptors by coated pits is diffusion-controlled for any value of the escaping rate constant (k-). This result is significantly different from our previous findings. In fact, for a zeroth order process, we find that either diffusion has no effect on k+ or, at the most, receptor trapping is 84% diffusion-controlled. Moreover, we find values for the receptor reinsertion rate constant (kappa), which range between 15% of the pit's invagination rate constant, lambda, and three halves lambda. In addition, the ratio kappa/lambda is equal to the ratio of the concentration of receptors in pits with respect to the internalized receptors. Comparison between the experimental radial distribution of receptors around pits and the theoretical should provide an indication of the diffusion effect on k+.
The localization of inhibin alpha-subunit in the human testis was studied at the light- and electron-microscope level with immunostaining techniques. Antibodies against specific fragments of porcine and human inhibin alpha-subunits were utilized. At light microscopy, inhibin alpha-subunit immunoreactivity was detected in Sertoli cells, spermatocytes and in some Leydig cells. At electron microscopy, gold labeling was found in the cisternae of the Golgi apparatus and in the endoplasmic reticulum of Sertoli and Leydig cells. Gold labeling for inhibin was also found in coated vesicles in the cytoplasm of Sertoli cells as well as in coated pits and coated vesicles in the cytoplasm of some spermatocytes. The results of the present study suggest that, in the human testis, inhibin is produced by Sertoli and Leydig cells and is taken up by spermatocytes, on which it might act in a paracrine manner.