The effects of lipolytic hormones on calcium uptake in endoplasmic reticulum of adipocytes.

To explore interrelationship between the roles of cAMP and calcium ion in hormone-stimulated lipolysis, cAMP accumulation in rat adipocytes and calcium binding in the endoplasmic reticulum were investigated with special reference to the effects of lipolytic hormones under various conditions. ACTH, isoproterenol, DBcAMP and aminophylline significantly increased ATP-dependent calcium uptake in adipocyte endoplasmic reticulum, but only after they were incubated with intact cells and not when they were added after homogenization. In vivo dexamethasone treatment and A-23187 accelerated, while 2.4-dinitrophenol blunted ACTH-stimulated lipolysis, cAMP accumulation and microsomal calcium uptake in parallel. Adrenalectomy, Mn2+ and adenosine enhanced ACTH-stimulated cAMP accumulation in adipocytes but lowered the calcium uptake and lipolysis. Thus, there was consistent parallelism between hormone-stimulated lipolysis and microsomal calcium uptake throughout the study. These data suggest that changes in the microsomal calcium uptake plays a crucial role in the regulation of hormone-induced lipolysis, irrespective of whether or not the intracellular cAMP concentration is involved in the lipolytic mechanism.