Mechanisms for termination of the action of dopamine in carotid body chemoreceptors.
The possible presence of a high affinity uptake mechanism for dopamine and the metabolism of this amine was investigated in the rabbit carotid body. The type I cells of this sensory organ contain high levels of dopamine and share with sympathetic nerve endings (which possess a high affinity uptake mechanism for catecholamines) the properties of being presynaptic catecholaminergic elements, but also have in common with chromaffin cells from intact adrenal medulla (which lack a high affinity catecholamine uptake) a similar embryological origin and ultrastructural appearance. Our experiments revealed only a low affinity uptake process (Km = 6.76 X 10(-4) M [3H]dopamine; Vmax = 1.84 X 10(-9) mol [3H]dopamine/mg protein/min) in the rabbit carotid body. In agreement with our kinetic findings, the uptake of [3H]dopamine was found to be independent of the Na+ concentration in the incubation media. The efflux from the tissue of incorporated [3H]dopamine was very fast (88% wash-out with a half-time of 4 min). DOPAC was the principal catabolite of dopamine in the carotid body, and the organ exhibited a very low capacity for norepinephrine synthesis. Neither chronic carotid sinus nerve section nor chronic sympathectomy modified the uptake of [3H]dopamine, suggesting that the lack of expression of a high affinity uptake was not a consequence of trophic suppression by the neural innervation of the organ. We conclude that overflow, or wash-out, of released dopamine may be quantitatively the most important mechanism for the inactivation of this putative neurotransmitter in the rabbit carotid body.
D000818:Animals; D001696:Biomechanical Phenomena; D002344:Carotid Body / Q000502:physiology*; D002346:Carotid Sinus / Q000502:physiology; D002628:Chemoreceptor Cells / Q000502:physiology*; D003714:Denervation; D004298:Dopamine / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D013562:Sympathectomy; D013997:Time Factors; D014316:Tritium
D014316:Tritium; D012964:Sodium; D004298:Dopamine