Relation between cytosolic free calcium and respiratory rates in cardiac myocytes
Moreno-Sánchez, R.; Hansford, R.G.
American Journal of Physiology 255(2 Pt 2): H347-H357
1988
ISSN/ISBN: 0002-9513 PMID: 3407793 Document Number: 319033
Rates of O2 uptake of isolated rat cardiac myocytes were determined as a function of cytosolic free Ca2+ concentration ([Ca2+]c) that was estimated from intracellular quin2 fluorescence. [Ca2+]c was increased by depolarization with K+ or veratridine. In each case, there was a correlation between increase in [Ca2+]c and stimulation of O2 uptake. Apparent exceptions seen on raising K+ were resolved on the grounds of an effect of osmolality on O2 uptake rates. Increase in O2 uptake and [Ca2+]c by veratridine was sensitive to variation of extracellular Na+, Ca2+, and pH in a way that suggests a major involvement of the Na+-Ca2+ exchange: partial inhibition by 2.7 .mu.M verapamil and total inhibition by 30 .mu.M 3',4'-dichlorobenzamil were consistent with this conclusion. Attempts were made to assess the quantitative significance of direct activation of respiration by Ca2+ at the level of mitochondrial dehydrogenases vs. an indirect mechanism involving increased ADP generation. Ruthenium red, which blocks the former process but not the latter, gave a small decrease in O2 uptake rates. However, activation of oxidative phosphorylation by ADP was predominant under these conditions of profound and sustained depolarization, based on a lowered mitochondrial NADH content in response to veratridine.