Effects of adrenergic agonists and mitochondrial energy state on the Ca transport systems of mitochondria.
246 - 254.
This study investigates the effects of adrenergic agonists and mitochondrial energy state on the activities of the Ca transport systems of female rat liver mitochondria. Tissue perfusion with the α-adrenergic agonist phenylephrine and with adrenaline, but not with the β-adrenergic agonist isoprenaline, induced significant activation of the uniporter and the respiratory chain. Uniporter activation was evident under two sets of experimental conditions that excluded influences of Δψ, i.e., at high Δψ, where uniporter activity was Δψ independent, and at low Δψ, where uniporter conductance was measured. Preincubation of mitochondria with extracts from phenylephrine-perfused tissue quantitatively reproduced uniporter activation when comparison was made with mitochondria treated similarly with extracts from tissue perfused without agonist. Similar, but more extensive, data were obtained with heart mitochondria pretreated with extracts from hearts perfused with the α-adrenergic agonist methoxamine. Phenylephrine did not affect Ca efflux mediated by the Na-Ca carrier or the Na-independent system. In contrast, the liver mitochondrial Na-Ca carrier was activated by tissue perfusion with isoprenaline; the Na-independent system was unaffected. Na-Ca carrier activation was not associated with any change in a number of basic bioenergetic parameters. It is concluded that the Ca transport systems of liver mitochondria may be controlled in an opposing manner by α-adrenergic agonists (promotion of Ca influx) and β-adrenergic agonists (promotion of Ca efflux). At Δψ values >110 mV, the Na-independent system was activated by increase in Δψ; the uniporter and Na-Ca carrier activities were insensitive to Δψ changes in this range. In consequence, decreased Δψ induced net Ca uptake during steady-state Ca cycling. This offers a further potential mechanism whereby liver mitochondrial Ca and Ca-sensitive oxidative metabolism may be autoregulated by the mitochondrial energy state. © 1987 American Chemical Society.
|Title:||Effects of adrenergic agonists and mitochondrial energy state on the Ca transport systems of mitochondria|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of)|
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