AJP - Heart and Circulatory Physiology, Vol 255, Issue 2 347-H357, Copyright © 1988 by American Physiological Society
Relation between cytosolic free calcium and respiratory rates in cardiac myocytes
R. Moreno-Sanchez and R. G. Hansford
Laboratory of Cardiovascular Science, National Institute on Aging, Baltimore, Maryland 21224.
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 exception seen on raising K+ were resolved on the 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 microM verapamil and total inhibition by 30
microM 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.
