Sorting and recycling efficiency of apical insulin binding sites during endocytosis in proximal tubule cells

Nielsen, Simone S. E.

doi:10.1152/ajpcell.1993.264.4.c810

Cited by 18 publications

(13 citation statements)

References 5 publications

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“…1997a). Moreover, in a study by Nielsen (1993) there were no further binding and tubular uptake of proteins (insulin) at 12 °C after saturation of the binding sites. We therefore consider the tubular reabsorption of proteins to be almost insignificant at 8 °C.…”

Section: Discussionmentioning

confidence: 91%

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

Sörensson

Ohlson

Lindström

et al. 1998

Acta Physiologica Scandinavica

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The classical concept of a negative glomerular charge barrier has recently been questioned, mainly based on the somewhat high clearance for anionic horseradish peroxidase (HRP). The validity of using anionic HRP can be tested by changing the properties of the charge barrier. A rather unequivocal approach is to reduce the ionic composition of the perfusate and hence increase the Debye length. We determined the glomerular clearance for horseradish peroxidase and serum albumin, using isolated rat kidneys perfused at 8 degrees C to reduce the tubular modification of the primary urine. The perfusate contained trace amounts of the neutral 125I-nHRP and the anionic 131I-aHRP and were otherwise identical except for different ionic strengths, 152 mM and 34 mM, respectively. During control, the fractional clearance (theta) was 0.11 +/- 0.015 for nHRP and 0.045 +/- 0.010 for aHRP, with an average clearance ratio (n/a) of 2.8 +/- 0.24. Low ionic strength reduced theta for aHRP to 0.027 +/- 0.006, giving an increased clearance ratio for HRP of 4.2 +/- 0.44. The existence of a negative charge barrier is supported by the experiments. The result obtained during normal perfusion is compatible with a charge density (omega) of 34 mEq L-1, using a model of homogeneously charged membrane. Low ionic strength perfusion reversibly reduced the concentration of fixed charges to 12 mEq L-1, suggesting an almost threefold increase of the glomerular membrane volume. Thus, the glomerular charge barrier should be regarded to have a dynamic gel structure rather than being a rigid membrane.

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Section: Discussionmentioning

confidence: 91%

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

Sörensson

Ohlson

Lindström

et al. 1998

Acta Physiologica Scandinavica

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“…This is highly unlikely. Because we perfused the kidneys at 8°C, there should be no significant cellular metabolism or uptake (31). There are, however, changes in viscosity at 8°C (ϳ2 times higher than at 37°C); the resistance to flow and filtration is twice as high, and diffusion is reduced by 50%.…”

Section: Discussionmentioning

confidence: 99%

A quantitative analysis of the glomerular charge barrier in the rat

Sörensson¹,

Ohlson²,

Haraldsson

2001

American Journal of Physiology-Renal Physiology

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Modifying the ionic strength (I) is a gentle way to alter charge interactions, but it cannot be done for studies of the glomerular sieving of proteins in vivo. We therefore perfused 18 isolated rat kidneys with albumin solutions of different ionic strengths at a low temperature (cIPK) to inhibit tubular uptake and protease activity. Four anionic proteins were studied, namely albumin (Alb), orosomucoid (Oro), ovalbumin (Ova), and anionic horseradish peroxidase (aHRP), together with the neutral polymer Ficoll. With normal ionic strength of the perfusate (152 mM), the fractional clearance (theta) was 0.0018 +/- 0.0003 for Alb, 0.0033 +/- 0.0003 for Oro, 0.090 +/- 0.008 for Ova, and 0.062 +/- 0.002 for aHRP. These theta values were all lower than for Ficoll of similar hydrodynamic size; e.g., theta(Ficoll 36 A) was >20 times higher than theta for albumin. Low ionic strength (34 mM) increased size selectivity as theta for anionic proteins and Ficoll fell, suggesting a reduction in small-pore radius from 44 +/- 0.4 to 41 +/- 0.5 A, P < 0.01. In contrast, low I reduced the charge density of the membrane, omega, to one-quarter of the 20--50 meq/l estimated at normal I. These dynamic changes in omega seem to be due to volume alterations of the charged gel, fluid shifts that easily are accounted for by the changes in electroosmotic pressures. The finding that low ionic strength induces inverse effects on size selectivity and charge density strongly suggests that separate structures of the glomerular wall are responsible for the two properties.

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“…One of the functions of the kidney proximal tubule cells is to internalize and degrade proteins and peptides that have filtered through the glomeruli via mechanisms involving receptor binding and/or fluid-phase endocytosis (Birn et al 1993;Nielsen 1993a;Sundin et al 1994). Ultrastructural investigations of these cells have revealed a well-developed "endocytic complex", including plasma membrane invaginations between the base of the microvilli, newly formed endocytic vesicles and large endocytic vacuoles in the apical cytoplasm (for reviews, see Kritz and Kaissling 1992;Maunsbach and Christensen 1992).…”

Section: Introductionmentioning

confidence: 99%

Apical tubular network in the rat kidney proximal tubule cells studied by thick-section and scanning electron microscopy

Hatae

Ichimura

Ishida

et al. 1997

Cell and Tissue Research

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The apical cytoplasm of several absorbing epithelia contains well-developed apical tubules (AT) which contribute to membrane recycling from endocytic vacuoles to the apical cell membrane. In this study, we examined three-dimensional structures of the AT in rat kidney proximal tubule cells by transmission and scanning electron microscopy. In thin sections, the AT appeared as straight tubules with a rather constant diameter (70-90 nm), but others were curved and, occasionally, branching. No AT were labeled with the marker for the external cell surface (ruthenium red) or exhibited histochemical enzyme activity for lysosomal hydrolase (acid phosphatase). After intravenous injection of horseradish peroxidase, it was absorbed in the kidney proximal tubule cells and the AT were labeled with HRP reaction products. Stereo-viewing of the labeled AT in thick sections revealed that they formed an interconnected tubular network. Scanning electron microscopy allowed a three-dimensional view of the AT, in which a network of branching and anastomosing tubules was revealed. These observations indicate that the AT are intracellular endosomal compartments which form an extensive tubular network in the apical cytoplasm. The possibility that this apical tubular network serves as a large membrane store for membrane recycling is discussed.

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Sorting and recycling efficiency of apical insulin binding sites during endocytosis in proximal tubule cells

Cited by 18 publications

References 5 publications

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

Glomerular charge selectivity for horseradish peroxidase and albumin at low and normal ionic strengths

A quantitative analysis of the glomerular charge barrier in the rat

Apical tubular network in the rat kidney proximal tubule cells studied by thick-section and scanning electron microscopy

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