TRYPANOSOMA-BRUCEI - DYNAMICS OF CALCIUM MOVEMENT BETWEEN THE CYTOSOL, NUCLEUS, AND MITOCHONDRION OF INTACT-CELLS

Targeted aequorins (CYT-AEQ, NUC-AEQ, and MT-AEQ) were used to measure Ca2+ concentrations within organelles of live trypanosomes. We determ ined that the nuclear envelope is a slight barrier to the free diffusi on of Ca2+. This situation was especially evident when Ca2+ influx acr oss the plasma membrane was stimulated with 200 nM melittin ([Ca2+](cy t) = 1.2 +/- 0.4 mu M and [Ca2+](nuc) = 0.85 +/- 0.15 mu M). By contra st, the ionophores nigericin (2.7 mu M) or monensin (2 mu g/ml) were u sed to induce Ca2+ efflux from the acidic storage compartment. Small t ransient elevations in [Ca2+](cyt) were observed (peaking at 660 +/- 2 00 and 580 +/- 120 nM, respectively). Parallel and equivalent changes in [Ca2+](nuc) were recorded. Active accumulation of Ca2+ into the nuc leus was not observed. Nigericin or monensin did not disrupt mitochond rial Ca2+ transport in vivo. Instead, the mitochondrion actively seque stered large quantities of Ca2+ in the presence of these ionophores, w ith peak values of 2.7 +/- 1.4 and 4.4 +/- 1.1 mu M, respectively. Ove rall, these data demonstrate that significant quantities of Ca2+ enter the nucleus following influx across the plasma membrane or following efflux from an intracellular acidic storage compartment. However. the magnitude of change for [Ca2+](cyt) and [Ca2+](nuc) is small compared to the total amount of exchangeable Ca2+ since the majority of release d Ca2+ is actively sequestered by the mitochondrion. (C) 1998 Academic Press.