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Uptake of high‐density lipoprotein by Y‐organs of the crab, Cancer antennarius . I. characterization in vitro and effects of stimulators and inhibitors
Author(s) -
Kang Byoung K.,
Spaziani Eugene
Publication year - 1995
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.940300105
Subject(s) - biology , hemolymph , incubation , medicine , cholesterol , endocrinology , lipoprotein , metabolism , biochemistry , high density lipoprotein
Cholesterol is the obligate precursor for ecdysteroid hormone synthesis by the ecdysial glands (Y‐organs) in crustaceans, and all cholesterol in the hemolymph is bound to high‐density lipoprotein (HDL). The mechanism was studied of how Y‐organ cells acquire cholesterol. Y‐organ segments were incubated with HDL isolated from hemolymph and labeled with 125 I. After incubation, tissue was homogenized in acid to determine radioactivity in acid‐precipitable (cell associated, intact) HDL and in acid‐soluble (degraded) HDL. Both HDL uptake and degradation showed saturation kinetics. At saturation most of the total counts represented degraded HDL; by 3 h, degradation was 80%. Rates of HDL uptake and breakdown were higher in Y‐organs from de‐eyestalked crabs (deprived thereby of molt‐inhibiting hormone, MIH) than in glands from intact crabs. Both parameters were depressed by inhibitors of glycolysis and oxidative phosphorylation dose dependently and by low temperature. HDL uptake also was depressed by cAMP added to the medium experimentally or through efflux from the tissue during incubation. These results indicate a mechanism for HDL uptake that entails receptor‐mediated, energy‐dependent endocytosis of the entire HDL‐cholesterol complex. Also the results suggest that HDL uptake and degradation are mediated by cAMP and depressed by an eyestalk factor, presumably MIH. © 1995 Wiley‐Liss, Inc.