Effect of myoglobin inactivation on intracellular gradients of NADH fluorescence at critical mitochondrial oxygen supply
E. Takahashi, H. Endoh, M. Ishikawa, M. Kishi, K. Doi

The purpose of the present study was to investigate in single cardiomyocytes isolated from the rat ventricle whether cytosolic myoglobin facilitates oxygen diffusion to mitochondria at a critical mitochondrial oxygen supply. We assessed oxygen transport to mitochondria by quantitative measurement of mitochondrial NAD(P)H fluorescence with a subcellular spatial resolution. Lowering the extracellular Po₂ to 15 - 30 Torr while stimulating mitochondrial respiration by an uncoupler of oxidative phosphorylation produced steep intracellular radial gradients of the NAD(P)H fluorescence. These intracellular heterogeneities of oxygenation should favor myoglobin facilitated oxygen diffusion. Then, we inactivated myoglobin by nitrite and examined the effect on radial NAD(P)H fluorescence gradients. Neither cellular oxygen consumption in uncoupled cardiomyocytes nor mitochondrial NAD(P)H fluorescence intensity for a given Po₂ in coupled cardiomyocytes was affected by nitrite. In contrast, myoglobin inactivation significantly elevated the mitochondrial NAD(P)H fluorescence level. Thus, myoglobin appears to facilitate intracellular oxygen diffusion in single cardiomyocytes at a critical mitochondrial oxygen supply.

Keywords: digital image processing, metmyoglobin, myoglobin facilitated oxygen diffusion, NADH fluorescence, single cardiomyocytes

Applied Cardiopulmonary Pathophysiology 9: 368-373, 2000

Eiji Takahashi, Ph.D.
Department of Physiology
Yamagata University School of Medicine
Yamagata  990-9585
Japan
E-mail: eiji@med.id.yamagata-u.ac.jp