Receptor-mediated endocytosis of alpha 2-macroglobulin by principal cells in the proximal caput epididymidis in vivo.
Micropuncture techniques were used to study receptor-mediated endocytosis of alpha 2-macroglobulin bound to colloidal gold (alpha 2M-gold) by principal cells in the proximal caput epididymidis of control and efferent duct-ligated rats. The pathway of receptor-mediated endocytosis of alpha 2-macroglobulin-gold in vivo was similar to that which occurs in vitro. Alpha 2-macroglobulin-gold was taken up and internalized in coated pits and coated vesicles and was localized sequentially in uncoated vesicles (endosomes), tubular-vesicular structures, multivesicular bodies, and lysosomes. However, a 100-fold excess of alpha 2-macroglobulin did not displace the uptake of alpha 2-macroglobulin-gold in principal cells from control rats. In contrast, uptake of alpha 2-macroglobulin-gold by principal cells from efferent duct-ligated rats was six-fold greater than in control rats, and could be displaced to control levels by a 100-fold excess of alpha 2-macroglobulin. It is suggested that the inability of a 100-fold excess of alpha 2-macroglobulin to displace uptake of alpha 2-macroglobulin-gold in control rats was due to the normal saturation of apparent alpha 2-macroglobulin receptors on principal cells. The effect of efferent duct ligation was to remove the high levels of endogenous alpha 2-macroglobulin, which depleted the receptors of alpha 2-macroglobulin, thereby allowing a higher uptake of alpha 2-macroglobulin-gold in the efferent duct-ligated rats.
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D000818:Animals; D003102:Colloids; D004705:Endocytosis; D004822:Epididymis / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D006046:Gold; D008026:Ligation; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D011677:Punctures; D051381:Rats; D011919:Rats, Inbred Strains; D011971:Receptors, Immunologic / Q000502:physiology*; D000511:alpha-Macroglobulins / Q000378:metabolism*
D003102:Colloids; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; D000511:alpha-Macroglobulins; D006046:Gold