Adenosine triphosphate content in the cat carotid body under different arterial O2 and CO2 conditions.

The adenosine triphosphate (ATP) level in the carotid body has often been discussed as the crucial step in the chemoreceptive process. Therefore, the ATP level of the cat carotid body was investigated with the aid of the bioluminescence method under different stimulation conditions. Under normoxic conditions an ATP level of about 0.087 nmol/glomus was measured, which is very low in comparison to other organs. The level did not change significantly, neither under hypoxic nor hypercapnic conditions. From these results we conclude that the primary effect of the chemoreceptive process in the carotid body cannot be explained by changes of the ATP level under different stimulation conditions.

The norepinephrine and dopamine content of the cat carotid body in vivo under normoxic and hypoxic conditions.

The norepinephrine (NE) and dopamine (DA) content of the cat carotid body (CB) in vivo was investigated under normoxic and hypoxic conditions (5% O2 for 1 h) by radiolabelling method. To avoid a large scattering of the measured values due to inhomogeneity of the biological material, young sib animals were used. The mean NE content under normoxia was 617 +/- 184 pmol/CB, and the mean DA content 451 +/- 200 pmol/CB. Under hypoxia, NE and DA were lowered significantly by 37% and 30%, respectively. From these results we conclude that both transmitters with their known excitatory and inhibitory actions probably influence the chemoreceptive elements in the carotid body.

An endogenous inhibitor of amine oxidase (flavine-containing) in the carotid body of the cat.

The activity of amine oxidase (flavine-containing) was measured in various organs. No activity could be detected in homogenates of the carotid body of the cat. Mixing experiments with this homogenate and rat liver mitochondria showed the presence of an inhibitor of amine oxidase activity in the carotid body. This inhibitor is inactivated by boiling. No inhibitor activity was found in the ganglion superior cervicale of the cat.

ATPases of the cat carotid body and of the neighbouring ganglia.

The average ATPase activity in homogenates of the cat carotid body is found to be 20 nmol Pi liberated per minute per mg fresh tissue weight at 25 degrees C. ATPase activity in the nodose ganglion and the superior cervical ganglion is found in the same range. Most of the activity remains in the supernatant after removal of the mitochondria by centrifugation. The activity is inhibited by ouabain only marginally (ganglia) or not at all (carotid body). In all these organs up to 80% of the activity is seen in the absence of Mg2+ and the presence of increasing concentrations of Ca2+.

Dopamine-beta-hydroxylase activity of the cat carotid body under different arterial O2 and CO2 conditions.

To determine the importance of dopamine and noradrenaline as neurotransmitters during chemoreception in the cat carotid body we investigated the contents of both compounds as well as the activity of dopamine-beta-hydroxylase (DBH) under different arterial PO2 and PCO2 conditions. The superior cervical ganglion was used as a control organ. In the carotid body and the ganglion an inverse relationship exists between the catecholamine content and the DBH activity. The carotid body has a high catecholamine content with a low DBH activity whereas the superior cervical ganglion has a low catecholamine content and high DBH activity. Hypercapnia did not produce any significant change in the catecholamine content or in the DBH content of the carotid body. However, in comparison with hyperoxia, hypoxia produced a significant change (p less than 0.05) in the noradrenaline content without changing the DBH activity. The dopamine content under these conditions did not change significantly. The results may indicate that the high catecholamine content of the carotid body is the result of a high retention and/or low rate of degradation rather than of a high rate of synthesis.

Oxygen consumption of the isolated carotid body tissue (cat).

The oxygen consumption of the isolated carotid body tissue measured in microchambers (volumes 12 and 20 mul) was 0.0051 mul O2/mg wet weight-min for an average of 54 measurements at 22 +/- 1 degree C, if the calculation was based on the oxygen pressure decrease of the surrounding medium measured polarographically in the range from 120 to 50 torr. It is bound to the presence of exogenous substrate and almost completely inhibited by antimycin but not significantly altered by addition of EGTA (4-16 mM) or Ca2+ (2 mM). Measurements performed at higher oxygen pressures (300 to 100 torr) in the medium show that the oxygen consumption of isolated carotid body tissue is independent of oxygen pressure at these high oxygen pressures. The findings obtained under the above conditions argue in favor of a mitochondrial oxygen consumption. The results are discussed with regard to data obtained with needle electrodes in the perfused organ.