The effect of epinephrine on calcium handling by adipocyte plasma membranes, endoplasmic reticulum, and mitochonrdia.

The effect of epinephrine treatment of adipocytes upon calcium handling by subsequently isolated plasma membranes, endoplasmic reticulum, and mitochondria has been examined and compared to the previously reported effects of insulin upon these parameters. Epinephrine (0.1 micrograms/ml) treatment of adipocytes resulted in: 1) a 19% increase in calcium binding to plasma membranes at calcium concentrations (2 and 250 microM) which reflect binding to the high and low affinity calcium-binding sites, respectively; 2) small but significant decreases in the maximum rate (-7.4%) and the Km (-12.6%) for calcium uptake by the endoplasmic reticulum without changes in the steady state capacity or the rate of efflux from the endoplasmic reticulum; and 3) no change in the stable pool of calcium in the mitochondria. The epinephrine-induced increase in calcium binding by the plasma membranes is identical to the effects of insulin previously reported, suggesting that this alteration may be involved in the similar membrane effects of these two hormones. In contrast, the effects of epinephrine on endoplasmic reticulum and mitochondrial calcium are strikingly different from the effects of insulin, suggesting that these parameters may be related to the vastly different effects that these hormones have on intracellular metabolic events.