The reversible inhibition by carbonyl cyanide m-chlorophenyl hydrazone of epinephrine-stimulated lipolysis in perifused isolated fat cells

Abstract

Lipolysis stimulated in perifused isolated fat cells by 0.5 μm epinephrine is an ATP-dependent process which can be monitored by measuring the release of glycerol. The stimulated lipolysis is inhibited by 10 μM carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an uncoupler of oxidative phosphorylation. If 20 mM glucose is continuously present in the perifusion medium during and after treatment with epinephrine and CCCP, the inhibition of the stimulated lipolysis is reversible when the CCCP is discontinued; otherwise it is not readily reversible. Since 20 mM 2-deoxyglucose will not substitute for glucose, metabolism of glucose beyond phosphorylation by hexokinase is concluded to be necessary in order to maintain the reversibility of the inhibition by CCCP. Substitution of 10 mM succinate for glucose also did not preserve the reversibility of the CCCP inhibition, and there was no significant difference in the amount of decrease of ATP in fat cells incubated with CCCP and epinephrine in the presence of glucose as compared to the decrease observed in the presence of succinate. The mechanism by which glucose maintains reversibility of the inhibition of stimulated lipolysis by CCCP is therefore not clear.