Enzyme histochemical investigations of the mammalian carotid body

Abstract

The carotid body (CB) in mammals is a small cluster of chemosensory and supporting cells located at the carotid bifurcation. It has been proposed that the chemoreceptor glomus cells release a variety of neurotransmitters that trigger upon hypoxia an action potential through the afferent fibers, thus conveying the chemosensory information to the central nervous system. By means of histochemical techniques the presence and distribution of certain metabolic enzymes was demonstrated in the CB of rats, guinea pigs and rabbits. In particular, we have revealed that the glomus cells expressed hydrolytic enzymes such as alkaline phosphatase (AP), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and ATPase as well as oxidoreductases including oxidases like monoamine oxidase (MAO) and dehydrogenases like succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), isocitrate dehydrogenase (IDH), glucose-6-phosphate dehydrogenase (G6PD), glutamate dehydrogenase (GDH) and NADPH dehydrogenase (NADPH-diaphorase). In addition, the sustentacular cells also contained, although in a much lesser degree, AP, BChE, LDH, G6PD, GDH and NADPH-d. Some AP and SDH activity was seen in the CB microvasculature as well. Our results provide evidence that the two types of parenchymal CB cells display a different enzyme content and that the glomus cells possess enzymatic properties necessary for the secretory process. It can also be inferred that the chemoreceptor function and the nerve impulse conduction need an intensive molecular and cation exchange, and energy supply.