Carbonic anhydrase in the carotid body and the carotid sinus nerve

Abstract

It is well known that carbonic anhydrase plays an important role in the physiological responses of carotid-body chemoreceptors to hypercapnia. Nevertheless the precise location of the enzyme within the carotid body has been a matter of controversy for many years. Using the Hansson method we found histochemical evidence that this enzyme is localized in type I cells. Type II cells and nerve terminals did not show enzymatic activity. These results allow us to define the carotid body as a secondary receptor in the context of the "acidic hypothesis" of transduction in the carotid body.

Physiological carbon dioxide, bicarbonate, and pH sensing

“…[147]). We have confirmed the presence of sAC in rat glomus cells by immunofluorescence (unpublished observations), which also express abundant intracellular carbonic anhydrase [148, 149]. Additionally, L-type Ca 2+ channels are activated by elevated CO 2 , independently of pH i , in rat locus coeruleus neurons [143], suggesting sAC could also be important in central chemosensing; however, direct functional evidence for the role of sAC as a molecular sensor of hypercapnia in the carotid body or in other peripheral and central chemoreceptors, is lacking.…”

Immunohistochemical localization of carbonic anhydrase isozymes in the rat carotid body

“…In this regard, other isozymes, e.g. membrane‐bound CA‐IV, may be present in type I cells, as other investigators have showed enzyme activity in the cell membrane (Ridderstrale & Hanson, 1984; Rigual et al. 1985).…”

“…In addition to these physiological studies, other groups showed the presence of CA in the carotid body by enzyme histochemistry (Becker et al. 1967; Ridderstrale & Hanson, 1984; Rigual et al. 1985; Nurse, 1990).…”

The carbonic anhydrase inhibitors methazolamide and acetazolamide have different effects on the hypoxic ventilatory response in the anaesthetized cat

“…Type I cells contain CA isoenzymes of which the precise subcellular locations remain to be elucidated except for the cytosolic isoforms CA II and III (possibly a membrane‐bound isoform is also involved Rigual et al 1985; Nurse, 1990; Botrè et al 1994; Ridderstråle & Hanson, 1984; Yamamoto et al 2003). There are ample data to indicate that in the carotid bodies, CA regulates the speed and magnitude of changes in intracellular pH of type I cells upon (removal of) sudden hypercapnic stimuli (Gray, 1971; Black et al .…”