CELLULAR AND SUBCELLULAR CALCIUM ION HOMEOSTASIS

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This project examines mechanisms whereby cells achieve homeostasis of Ca2+ ion concentrations, both within the cytosol and within other cellular compartments, yet allow changes in Ca2+ in response to hormones and neurotransmitters. This year we have continued investigations into the rol the proton-oncogene bcl-2 in altering Ca2+ transport by the endoplasmic reticulum (ER) of a line of T-lymphocytes (Jurkats), concomitantly with affording the cells some degree of protection against apoptosis, induced by the withdrawal of growth factors in serum. We showed that the overexpression of the bcl-2 gene resulted in larger pools of Ca2+ both within the ER and the mitochondria of Jurkat cells, when these were stresse by serum-starvation. This accumulation occurred despite the lack of an increase in resting Ca2+ concentration of the cytosol. Other recent studie have linked ER Ca2+ content with the potential for cell growth, and studies from this lab have shown that, within a certain range, an increased mitochondrial Ca2+ content potentiates energy production by oxidative phosphorylation. In a second area, in collaboration with the Cardiac Function Section, and the Division of Cardiology, Johns Hopkins University, we have looked for direct effects of ~-adrenergic stimulation of the heart upon the Ca2+- transport properties of subsequently-isolated mitochondria. The reason for interest is that ~-adrenergic stimulation of cardiac myocytes was shown to raise mitochondrial free Ca2+ in the absence of changes in cytosol Ca2+. Such an increase would have a positive impact on the potential for oxidativ phosphorylation (see reports of years '91,'92). In turn, the efficacy of beta-adrenergic activation is diminished in the aging heart, potentially blunting responses of energy production. Preliminary findings indicate a ~ adrenergic activation of both mitochondrial Ca2+ uptake and release, which is stable to the isolation of mitochondria.