Simulation of cardiac work transitions, in vitro: Effects of simultaneous Ca2+ and ATPase additions on isolated porcine heart mitochondria

P. R. Territo, S. A. French, R. S. Balaban

Research output: Contribution to journalArticle

42 Scopus citations

Abstract

During increases in cardiac work there are net increases in cytosolic [Ca2+] and ATP hydrolysis by myofiliments and ion transport ATPases. However, it is still unclear what role Ca2+ or the ATP hydrolysis products, ADP and Pi, have on the regulation of mitochondrial ATP production. In this study, work jumps were simulated by simultaneous additions of Ca2+ and ATPase to porcine heart mitochondria. The net effects on the mitochondrial ATP production were monitored by simultaneously monitoring respiration (mVo2), [NADH], [ADP] and membrane potential (Δψ) at 37°C. Addition of exogenous ATPase (300mIU.ml-1) + ATP (3.4mM) was used to generate a 'resting' background production of ADP. This resting metabolic rate was 200% higher than the quiescent rate while [NADH] and Δψ were reduced. Subsequent ATPase additions (1.3IU.ml-1) were made with varying amounts of Ca2+ (0 to 535 nM) to simulate step increases in cardiac work. Ca2+ additions increased mVo2 and depolarized Δψ, and were consistent with an activation of F0/F1ATPase. In contrast, Ca2+ reduced the [NADH] response to the ATPase addition, consistent with Ca2+ -sensitive dehydrogenase activity (CaDH). The calculated free ADP response to ATPase decreased <2-fold in the presence of Ca2+. The addition of 172nM free Ca2+ ATPase increased mVo2 by 300% (P≤0.05, n=8) while Δψ decreased by 14.9±0.1 mV without changes in [NADH] (P>0.05, n=8), consistent with working heart preparations. The addition of Ca2+ and ATPase combined increased the mitochondrial ATP production rate with changes in Δψ, NADH and [ADP], consistent with an activation of CaDH and F0/F1ATPase activity. These balancing effects of ATPase activity and [Ca2+] may explain several aspects of metabolic regulation in the heart during work transitions in vivo.

Original languageEnglish (US)
Pages (from-to)19-27
Number of pages9
JournalCell Calcium
Volume30
Issue number1
DOIs
StatePublished - Jan 1 2001
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Molecular Biology
  • Cell Biology

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