Kinetics of receptor-mediated endocytosis of albumin in cells derived from the proximal tubule of the kidney (opossum kidney cells): influence of Ca2+ and cAMP
| Autor: | Michel Gekle, Stefen Silbernagl, Sigrid Mildenberger, Ruth Freudinger |
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| Rok vydání: | 1995 |
| Předmět: |
medicine.medical_specialty
Physiology Clinical Biochemistry Endocytosis Kidney Tubules Proximal chemistry.chemical_compound Physiology (medical) Internal medicine Albumins medicine Extracellular Cyclic AMP Animals Cyclic adenosine monophosphate Receptor Fluorescein isothiocyanate Cells Cultured Bafilomycin Receptor-mediated endocytosis Opossums Hydrogen-Ion Concentration Kinetics Endocrinology chemistry Bucladesine Ionomycin Biophysics Calcium Fluorescein-5-isothiocyanate |
| Zdroj: | Pflugers Archiv : European journal of physiology. 430(3) |
| ISSN: | 0031-6768 |
| Popis: | In this study we investigated the effects of Ca2+ and cyclic adenosine monophosphate (cAMP) on the kinetic of receptor-mediated (RME) and fluidphase (FPE) endocytosis in opossum kidney (OK) cells, derived from the proximal tubule of the kidney. We used fluorescein isothiocyanate (FITC)-labelled albumin and FITC-labelled dextran as endocytotic substrates for RME and FPE, respectively. Removal of extracellular Ca2+ led to a dramatic decrease of the apparent affinity of RME, but did not influence the maximum endocytotic uptake rate (Jmax). Reduction of extracellular Ca2+ to 1 μmol/l had no effect. Apparent affinity of specific binding of albumin to the plasma membrane was increased to 200% of control in the absence of extracellular Ca2+, whereas maximum binding capacity was slightly decreased. FPE was not affected by removal of extracellular Ca2+. Additional removal of cytoplasmic Ca2+, using ionomycin, had no further effect on RME and did not affect FPE. Increases of cytoplasmic (using ionomycin at extracellular Ca2+ concentrations of 1 μmol/l or 1.2 mmol/l) or extracellular Ca2+ did not alter the kinetics of RME or FPE. Dibutyryl-cAMP reduced Jmax but left the apparent affinity of RME unchanged. FPE and albumin binding to the plasma membrane were not changed in the presence of cAMP. Removal of extracellular Ca2+ and addition of cAMP led to an alkalinization of endocytotic vesicles. Yet the alkalinization induced by removal of Ca2+ was significantly greater as compared to the alkalinization in the presence of cAMP. Endosomal alkalinization with bafilomycin A1 had no further effect in the absence of Ca2+, but reduced RME in the presence of cAMP. From these results we conclude that cAMP and extracellular Ca2+ influence the kinetics of RME in proximal tubular cells. The action of Ca2+ removal seems to be mediated partially by changes of endosomal pH. Ca2+ seems to be a prerequisite for RME but not a regulator, whereas cAMP may act as physiological inhibitor of RME. |
| Databáze: | OpenAIRE |
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