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Calcium transport in rat liver mitochondria

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posted on 2023-05-26, 21:26 authored by Juzu, HA
In the present study, it was found that various components of the rat cytosol affect Ca¬¨‚⧂ÄövÖ‚à´ transport into and out of mitochondria when examined in vitro. The ¬¨‚â•H-palmitate-binding protein when saturated with palmitate caused Ca¬¨‚⧂ÄövÖ‚à´ release. The Ca-binding protein and albumin helped prolong Ca¬¨‚⧂ÄövÖ‚à´ retention in the mitochondria. Palmitoyl CoA and palmitate caused release of Ca¬¨‚⧂ÄövÖ‚à´ from preloaded mitochondria. On the other hand palmitoylcarnitine caused Ca¬¨‚⧂ÄövÖ‚à´ retention. The mitochondria were able to accumulate 4 - 9 % of the externally added Mg¬¨‚⧂ÄövÖ‚à´. The presence of varying concentration of external Mg¬¨‚⧂ÄövÖ‚à´ did not inhibit or increase Ca¬¨‚⧂ÄövÖ‚à´ uptake by the mitochondria, however, the extra Mg¬¨‚⧂ÄövÖ‚à´ accumulated prolonged Ca¬¨‚⧂ÄövÖ‚à´ retention in the mitochondria. During Ca¬¨‚⧂ÄövÖ‚à´ release from the mitochondria, there was a corresponding release of mitochondrial Mg¬¨‚⧂ÄövÖ‚à´. During Ca¬¨‚⧂ÄövÖ‚à´ retention, the level of mitochondrial Mg¬¨‚⧂ÄövÖ‚à´ remained steady. ATP or respiratory substrate was required for Ca¬¨‚⧂ÄövÖ‚à´ uptake. The presence of both respiratory substrate and ATP favoured Ca¬¨‚⧂ÄövÖ‚à´ retention. During Ca¬¨‚⧂ÄövÖ‚à´ release induced by palmitoyl CoA, PEP or glucose plus hexokinase, the total ATP concentration (i.e. that in the medium plus mitochondria) decreased, while the total AMP increased. During prolonged Ca¬¨‚⧂ÄövÖ‚à´ retention in the mitochondria, a high concentration of total ATP and a low concentration of total AMP was observed. The findings of Lehninger et al (1978) (that a more oxidised steady state of the mitochondrial pyridine nucleotide favours Ca¬¨‚⧂ÄövÖ‚à´ release and a relatively reduced state favours Ca¬¨‚⧂ÄövÖ‚à´ retention) was confirmed and further extended in this study. The adenine nucleotides were not significantly different from the control during Ca¬¨‚⧂ÄövÖ‚à´ release in the presence of the oxidants of mitochondrial NADH such as acetoacetate or oxaloacetate. Bovine serum albumin or ethane-1-hydroxy-diphosphonic acid (EHDP), substances known to help Ca¬¨‚⧂ÄövÖ‚à´ retention in the mitochondria, caused the Ca¬¨‚⧂ÄövÖ‚à´ released from the mitochondria by oxaloacetate to be taken up again. Externally added NAD‚ÄövÖ‚à´ and possibly NADH prolonged Ca¬¨‚⧂ÄövÖ‚à´ retention in the mitochondria. On the other hand, NADPH caused an earlier Ca¬¨‚⧂ÄövÖ‚à´ release. NADP‚ÄövÖ‚à´ did not affect Ca¬¨‚⧂ÄövÖ‚à´ uptake or release, The effect of cAMP on Ca¬¨‚⧂ÄövÖ‚à´ release was reinvestigated in the present study based on the findings of Lehninger et al (1978) and Christiansen (1977). Cyclic AMP caused Ca¬¨‚⧂ÄövÖ‚à´ release provided that palmitoyl CoA or palmitoylcarnitine were substrates and that the mitochondria prepared from fed rats were used within 1 hr after isolation. It was also noted in this study that the mitochondria isolated from starved rats had a lower NADH/NAD‚ÄövÖ‚à´ ratio and released their Ca¬¨‚⧂ÄövÖ‚à´ earlier than the mitochondria from fed rats. It was suggested that cAMP stimulates Ca¬¨‚⧂ÄövÖ‚à´ release from the mitochondria presumably by altering the redox state of the mitochondrial pyridine nucleotides.

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Copyright 1980 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1982. Bibliography: l. 234-249

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