Effects of spermine on mitochondrial Ca2+ transport and the ranges of extramitochondrial Ca2+ to which the matrix Ca2+-sensitive dehydrogenases respond

Abstract

1. Spermine has previously been reported to be an activator of mitochondrial Ca2+ uptake [Nicchitta & Williamson (1984) J. Biol. Chem. 259, 12978-12983]. This is confirmed in the present studies on rat heart, liver and kidney mitochondria by using the activities of the Ca2+-sensitive intramitochondrial dehydrogenases (pyruvate, NAD+-isocitrate and 2-oxoglutarate dehydrogenases) as probes for matrix Ca2+, and also, for the heart mitochondria, by using entrapped fura-2. 2. As also found previously [Damuni, Humphreys & Reed (1984) Biochem. Biophys. Res. Commun. 124, 95-99], spermine activated extracted pyruvate dehydrogenase phosphate phosphatase. However, it was found to have no effects at all on the extracted NAD+-isocitrate or 2-oxoglutarate dehydrogenases. It also had no effects on activities of the enzymes in mitochondria incubated in the absence of Ca2+, or on the Ca2+-sensitivity of the enzymes in uncoupled mitochondria. 3. Spermine clearly activated 45Ca uptake by coupled mitochondria, but had no effect on Ca2+ egress from mitochondria previously loaded with 45Ca. 4. Spermine (with effective Km values of around 0.2-0.4 mM) caused an approx. 2-3-fold decrease in the effective ranges of extramitochondrial Ca2+ in the activation of the Ca2+-sensitive matrix enzymes in coupled mitochondria from all of the tissues. The effects of spermine appeared to be largely independent of the other effectors of mitochondrial Ca2+ transport, such as Mg2+ (inhibitor of uptake) and Na+ (promoter of egrees). 5. In the most physiological circumstance, coupled mitochondria incubated with Na+ and Mg2+, the presence of saturating spermine (2 mM) resulted in an effective extramitochondrial Ca2+ range for matrix enzyme activation of from about 30-50 nM up to about 800-1200 nM, with half-maximal effects around 250-400 nM-Ca2+. The implications of these findings for the regulation of matrix and extramitochondrial Ca2+ are discussed.

Mitochondrial matrix granules: Their behavior during changing metabolic situations and their relationship to contact sites between inner and outer mitochondrial membranes

“…Since, however, earlier estimates of mitochondria1 calcium, based on equilibrium thermodynamic considerations, were in the millimolar range, a physiological correlation was not evident. But use of the calcium-sensitive probes, fura-2 or indo-1, made monitoring of the free calcium during changing energy metabolism possible (McCormack, 1989;Wan et al, 1989). These studies were performed on isolated mitochondria and so extrapolation to the in vivo situation is more or less speculative.…”

“…Studies using NMR techniques (Balaban and Heineman, 1989) have demonstrated that the concentrations of these compounds for oxidative phosphorylation do not change appreciably throughout the cardiac cycle and during increases in cardiac work. Hence, the regulation of energy production by calcium ions, present in the mitochondrial matrix, has been studied recently (McCormack, 1989;Wan et al, 1989). Three exclusively intramitochondrial dehydrogenases (e.g., pyruvate dehydrogenase, iso-citrate dehydrogenase, and 2-0x0-glutarate dehydrogenase) are key enzymes for the regulation of oxidative metabolism.…”

Effects of IP3, Spermine, and Mg2+ on Regulation of Ca2+ Transport by Endoplasmic Reticulum and Mitochondria in Permeabilized Pancreatic Islets

“…Spermine, which increases Ca 2+ uptake by isolated mitochondria from liver (7,8,12,13), brain (8), heart (8,13), and kidney (13), has now been shown to decrease the free-Ca 2+ concentration also in the incubation medium of permeabilized pancreatic islets, presumably through the same mech-anism. Mg 2+ , which antagonizes the effects of spermine on Ca 2+ uptake of mitochondria from different tissues (8), increased the free-Ca 2+ concentration in the incubation medium of permeabilized pancreatic islets.…”

Regulation of ornithine decarboxylase and polyamine import by hypoxia in pulmonary artery endothelial cells

“…It has been recognized for many years that precise adjustments in polyamine pools are required for cell growth and differentiation (20). More recent data indicate that the polyamines exhibit substantial antioxidant activity (14,27), regulate certain ion channels and receptors (6,7,17), and modulate a number of mitochondrial functions (21,30). Given the apparent central role of polyamines in regulating cell proliferative and functional states, their importance in governing responses of pulmonary vascular cells in hypoxia seems likely.…”