Involvement of the Endoplasmic Reticulum of ChromaffinCells of the Rat Adrenal Gland in Calcium Signaling

摘要

We studied the involvement of the endoplasmic reticulum (ER) in calcium signaling in rat chromaffin cells.For this purpose, the following agents influencing the activity of the ER were used: (i) Caffeine that activatesthe release of Ca~(2+)from the endoplasmic store and (ii) thapsigargin that suppresses accumulation of calciumin the ER. The intracellular Ca~(2+)concentration was measured with the help of a calcium-sensitive dye, Fura-2AM, using the microfluorescent technique. Applications of caffeine led to a rise in the level of free Ca2+ inthe cell cytosol and also to a decrease in the amplitude of calcium transients induced by depolarization ofthe plasma membrane under the action of a hyperpotassium solution. Under conditions of repeated caffeineapplications, the amplitude of transients decreased to 9% of its initial value, which is explained by exhaustionof the calcium stores. The action of caffeine was restored when the calcium stores were re-filled under theaction of depolarization of the plasma membrane. Thapsigargin completely removed the effect of caffeineand did not influence KC1-induced transients. Therefore, our experiments are indicative of a significantimportance of the ER calcium stores for calcium signaling in chromaffin cells, which allows us to hypothesizethat these stores play an important role in the control of secretion of catecholamines.