The role of mitochondria in the regulation of calcium influx into Jurkat cells.

Abstract

In electrically nonexcitable cells the activity of the plasma membrane calcium channels is controlled by events occurring in mitochondria, as well as in the lumen of the endoplasmic reticulum. Thapsigargin, a specific inhibitor of endoplasmic reticulum Ca2+-ATPase, produces the release of calcium from the endoplasmic reticulum and thus, activation of store-operated calcium channels in the plasma membrane. However, thapsigargin failed to produce significant activation of the channels in Jurkat cells that had been pretreated with mitochondria-directed agents: an uncoupler (carbonyl cyanide m-chlorophenylhydrazone) and oligomycin. This is in spite of the fact that Jurkat cells pretreated with carbonyl cyanide m-chlorophenylhydrazone plus oligomycin are otherwise energetically competent, due to a high rate of glycolysis and the inhibition of mitochondrial F1Fo-ATPase by oligomycin. The pool of intracellular ATP was found not to be influenced by the pretreatments of cells with oligomycin or with oligomycin plus carbonyl cyanide m-chlorophenylhydrazone. In the control cells, we found that the ATP pool amounted to 23.2 +/- 1.9 nmoles per 107 cells (n = 4). In cells pretreated with oligomycin the level of ATP was 21.8 +/- 1.9 nmoles per 107 cells (n = 4), and in cells pretreated with both oligomycin and an uncoupler the level of ATP was 22.1 +/- 0.2 nmoles per 107 cells (n = 3). Moreover, in cells pretreated with oligomycin plus carbonyl cyanide m-chlorophenylhydrazone and suspended in a nominally calcium-free medium, thapsigargin produces transient increases in cytosolic calcium identical to those in the control cells. Thus, this pretreatment does not modify either the content of intracellular calcium stores and/or the activity of calcium ATPase in the plasma membrane. Similar results were obtained when Jurkat cells were challenged by myxothiazol, a potent inhibitor of mitochondrial cytochrome bc1 oxidoreductase. Thapsigargin, although producing calcium release from intracellular stores, was ineffective in triggering the activation of calcium channels in the plasma membrane in the case of cells pretreated with myxothiazol and oligomycin. Our results suggest that coupled mitochondria participate directly in the control of calcium channel activity in the plasma membrane of Jurkat cells. When the mitochondrial protonmotive force is collapsed, either by carbonyl cyanide m-chlorophenylhydrazone or myxothiazol, the channel remains inactive even under conditions of empty intracellular calcium stores.