Oxidative phosphorylation in the rat arterial smooth muscle

Morphological, stereological, biochemical and physiological techniques were used to investigate the smooth muscle oxidative phosphorylation activity of the rat arteries, particularly small arteries with a diameter about 500 µm. The major object of the research was the rat tail artery. Morphological and stereological analysis found that the differences between the elastic arteries, muscular arteries and arteriole were mainly in the contents of smooth muscle. In the rat thoracic aorta, the smooth muscle volume fraction was 43.7±3.7% of the vessel wall. The proportion of the smooth muscle layers to the elastic lamella of this artery was about 1: 1. The rat femoral and tail arteries had smooth muscle contents of 82.5±3.1 % and 79.3±1.3%. The proportions of the smooth muscle layers to the elastic lamella of these two arteries were 5-11:1 and 6-14:1. The smooth muscle in the arteriole was 57.2±3.1 % with very little elastic tissue. The mitochondrial volume fractions in the arterial vascular smooth muscle cells of the aorta, arterioles, tail and femoral arteries were 6.9±0.8%, 7.8±1.0%, 8.4±0.7% and 7.8±0.7%. The mean value of the mitochondrial volume fraction for all arteries studied was 7.7%. All blood vessels had a similar range of mitochondrial volume fraction. Regardless of the arterial class, the mitochondrial volume fraction appears to account for approximately 8% of the volume of the arterial smooth muscle cells of all arteries chosen in the rat. On the basis of that value, the mitochondrial contents for the entire arterial walls for the aorta, tail and femoral arteries were 3.5%, 6.3% and 6.6%. The cytochrome c oxidase activities of the arteries and cardiac muscle were measured biochemically and found to be 3.8±0.38 µmol.min-1.g-1 and 9.6±0.50 µmol.min-1.g-1 for the aorta and tail artery, and 93.8±19.3 µmol.min-1.g-1 for the cardiac muscle respectively. Because the mitochondrial contents of the aorta, tail artery and cardiac muscle were 3.5%, 6.3% and 29%, the cytochrome c oxidase activities for the smooth muscle mitochondria of aorta and tail artery are 108 µmol.min-1.g-1 and 152 µmol.min-1.g-1, with 324 µmol.min-1.g-1 for the mitochondria of the cardiac muscle. This gives the calculated cytochrome c oxidase activities of the rat aorta and the tail artery as approximately 240 µmol.h-1.g-1 and 600 µmol.h1.g-1 respectively. The physiological oxidative phosphorylation capacity was measured by the perfusion of isolated rat tail arteries. Under air oxygen tension, the basal oxygen consumption was 103.1±6.8 µmol.h-1.g-1at37°C. The uncoupler 2-4 dinitrophenal (DNP) induced increase of oxygen uptake was 143.0±16.9 µmol.h-1.g-1. The total oxygen uptake after the infusion of DNP was 247.1±12.7 µmol.h-1.g-1. This suggests that the physiological oxidative capacity may be about 40% of the theoretical oxidative capacity in a rat tail artery. Tail artery perfusions oxygenated with 95% oxygen gave higher values of oxygen consumption although these measurements were necessarily less accurate.