Cellular compartment

About: Cellular compartment is a research topic. Over the lifetime, 1082 publications have been published within this topic receiving 53794 citations. The topic is also known as: cell compartmentation.

Resolution of cellular compartments involved in membrane potential changes accompanying IgE-mediated degranulation of rat basophilic leukemia cells.

Abstract: The overall membrane potential of rat basophilic leukemia cells (RBL-2H3) calculated from the transmembrane distribution of the lipophilic, tritium-labelled cation tetraphenyl-phosphonium [( 3H]TPP+) was resolved into its mitochondrial and plasma membrane potential components. Using the mitochondrial uncoupler carbonylcyanide-p-trifluormethoxyphenyl hydrazone (FCCP) which collapses the mitochondrial potential, it was shown that about one third of the overall potential resulted from the mitochondrial contribution. Degranulation of the RBL cells induced by two different IgE-cross-linking agents (specific antigen and anti-IgE antibodies), was accompanied by, and well correlated with, a decrease in the overall potential. However, evaluation of the source of these observed potential changes revealed that the FCCP-insensitive fraction of the overall potential, delta psi P, (representing the plasma membrane potential), was not affected. In contrast, the FCCP-sensitive component due to the mitochondrial potential decreased when receptor cross-linking increased. Thus, the observed decrease in the overall potential is most probably a secondary event in the sequence leading from stimulus to secretion. Indeed, exposure of the RBL cells either to a high external concentration of K+ ions or to a high amount of external TPP+, both causing depolarization, failed to trigger degranulation. It is suggested that the apparent decrease in the measured overall potential is a reflection of the mitochondrial membrane depolarization. The latter is most probably caused by mitochondrial Ca2+ uptake initiated by the increase in the intracellular concentration of Ca2+ which follows cells activation.

Hormonal stimulation, mitochondrial Ca2+ accumulation, and the control of the mitochondrial permeability transition in intact hepatocytes.

Abstract: Ca2+ functions as an intracellular signal to transfer hormonal messages to different cellular compartments, including mitochondria, where it activates intramitochondrial Ca2+-dependent enzymes. However, excessive mitochondrial Ca2+ uptake can promote the mitochondrial permeability transition (MPT), a process known to be associated with cell injury. The factors controlling mitochondrial Ca2+ uptake and release in intact cells are poorly understood. In this paper, we investigate mitochondrial Ca2+ accumulation in intact hepatocytes in response to the elevation of cytosolic Ca2+ levels ([Ca2+]c) induced either by a hormonal stimulus (vasopressin), or by thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+ pump. After stimulation, cells were rapidly permeabilized for the determination of the mitochondrial Ca2+ content (Ca2+ m) and to analyze the susceptibility of the mitochondria to undergo the MPT. Despite very similar levels of [Ca2+]c elevation, vasopressin and thapsigargin had markedly different effects on mitochondrial Ca2+ accumulation. Vasopressin caused a rapid (< 90 sec), but modest (< 2 fold) increase in Ca2+ m that was not further increased during prolonged incubations, despite a sustained [Ca2+]c elevation. By contrast, thapsigargin induced a net Ca2+ accumulation in mitochondria that continued for up to 30 min and reached Ca2+ m levels 10–20 fold over basal. Accumulation of mitochondrial Ca2+ was accompanied by a markedly increased susceptibility to undergo the MPT. Both mitochondrial Ca2+ accumulation and MPT activation were modulated by treatment of the cells with inhibitors of protein kineses and phosphatases. The results indicate that net mitochondrial Ca2+ uptake in response to hormonal stimulation is regulated by processes that depend on protein kinase activation. These controls are inoperative when the cytosol is flooded by Ca2+ through artificial means, enabling mitochondria to function as a Ca2+ sink under these conditions. (Mol Cell Biochem 174: 173–179,1997)