[Effects of Ca2+ and calmodulin inhibitors on lipolysis induced by epinephrine, norepinephrine, caffeine and ACTH in rat epididymal adipose tissue].

The effects of Ca2+ and calmodulin inhibitors on lipolysis induced by epinephrine, norepinephrine, caffeine and ACTH in rat epididymal adipose tissue were investigated. 1. Omission of Ca2+ from the incubation medium slightly depressed lipolysis induced by epinephrine, norepinephrine and ACTH. Lipolysis induced by caffeine was significantly depressed. 2. Lipolysis induced by epinephrine, norepinephrine, caffeine and ACTH was strongly depressed when Ca2+-deficient tissue was incubated in Ca2+-free Ringer solution. 3. In Ca2+-deficient tissue, the addition of 0.75mM Ca2+ apparently restored lipolysis induced by epinephrine, norepinephrine and ACTH, whereas that by caffeine was restored to only approximately 89%. 4. The addition of La3+ markedly inhibited lipolysis induced by each agonist. 5. The Ca2+ antagonists such as verapamil and diltiazem dose-dependently inhibited lipolysis induced by each agonist. 6. The specific calmodulin inhibitors such as chlorpromazine, trifluoperazine and W-7 markedly inhibited lipolysis induced by each agonist. These results strongly support the possible key role that the redistribution and influx of Ca2+ may play in lipolysis induced by epinephrine, norepinephrine, caffeine and ACTH, and further suggest that calmodulin may affect lipolysis.