Abstract
Incubation of isolated rat hepatocytes with vanadate (0.25, 0.5 and 1 mM) resulted in progressive accumulation of Ca 2+ in the intracellular compartments. Vanadate- induced Ca 2+ accumulation was related to inhibition of the plasma membrane Ca 2+-extruding system, but did not involve either enhanced plasma membrane permeability to Ca 2+ or the enhanced operation of a putative Na +/Ca 2+ exchanger. After an initial rise in the cytosolic free Ca 2+ concentration, as revealed by phosphorylase activation, Ca 2+ was sequestered predominantly by the mitochondria with little contribution from the endoplasmic reticulum. As the amount of Ca 2+ in the mitochondria increased, a progressive decrease in mitochondrial membrane potential occurred, together with an impairment of the ability of these organelles to further sequester Ca 2+. Associated with this, there was a decrease in intracellular ATP level, formation of surface blebs and cytotoxicity. Addition of an uncoupler to vanadate-treated hepatocytes dramatically accelerated the appearance of plasma membrane blebs and toxicity. Our results demonstrate that under conditions in which the plasma membrane Ca 2+ pump is inhibited, mitochondria play an important role in protecting hepatocytes against damage induced by Ca 2+ overload.
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