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Different pools of esterified arachidonic acid in rabbit kidney medulla: Relationship to Ca 2+ ‐stimulated prostaglandin biosynthesis
Author(s) -
Erman A.,
Azuri R.,
Raz A.
Publication year - 1982
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02535090
Subject(s) - arachidonic acid , chemistry , prostaglandin , biochemistry , renal medulla , endogeny , metabolism , prostaglandin e2 , kidney , biosynthesis , endocrinology , biology , enzyme
We investigated the effect of Ca 2+ ions on renal medulla metabolism of endogenous esterified arachidonic acid in contrast to that of radioactive arachidonate incorporated into medullary lipids. Some striking differences between the release of unlabeled prostaglandin E 2 and of 14 C‐labeled prostaglandin E 2 and arachidonic acid were seen in incubations in absence or presence of Ca 2+ ions. These differences indicated that exogenous [ 14 C] arachidonate incubated with medulla slices is incorporated into both Ca 2+ ‐sensitive and Ca 2+ ‐insensitive lipid pools of esterified arachidonate and furthermore, the Ca 2+ ‐sensitive pool is itself heterogeneous and consists of at least 2 functionally different lipid pools of esterified arachidonate. The first Ca 2+ ‐sensitive pool is characterized by a higher arachidonate turnover rate and incorporates more rapidly added radioactive arachidonate. The acylhydrolase activity which releases arachidonate from this pool is not efficiently coupled to prostaglandin endoperoxide synthase. In contrast, the second Ca 2+ ‐sensitive lipid pool has a slower arachidonate turnover rate and, consequently, a slower incorporation of added 14 C‐acid. The acylhydrolase activity associated with this pool is more tightly coupled to prostaglandin endoperoxide synthase, so that a higher portion of released arachidonate is converted to prostaglandin E 2 . Studies on arachidonic acid metabolic transformations using exogenously radioactive free acid added to tissues should therefore be inerpreted with caution because the results obtained may not reflect accurately the metabolic fate of endogenous, lipid‐esterified arachidonate which is released and metabolized under physiological conditions in vivo.