Effects of Carbonic Anhydrase Inhibition on the Responsiveness of Laryngeal Receptors in Cats to CO₂

Abstract

The effects of carbonic anhydrase inhibition on the responsiveness to CO 2 of pressure-sensitive laryngeal receptors were examined in anaesthetised, paralysed cats. Laryngeal CO 2 -sensitive receptors from the superior laryngeal nerve were selected by their responsiveness to intralaryngeal pressure and to perfusion of solution equilibrated with 9 % CO 2 . The carbonic anhydrase inhibitor, methazolamide, when given intralaryngeally at 10 _4 M, diminished or abolished the responses to the CO 2 -equilibrated solution in four of six pressure-sensitive receptors. Histochemical staining for carbonic anhydrase activity showed that the larynges perfused with methazolamide had diminished carbonic anhydrase activity, especially on the superficial layers of surface epithelium. Compared to untreated controls, when given intravenously (50 mg kg

Effects of CO2 and H+ on laryngeal receptor activity in the perfused larynx in anaesthetized cats

“…The mechanisms of the action of CO 2 on laryngeal receptors are not clear, but it would be expected that acidification of the receptor cell or its microenvironment would be responsible. The fact that the CO 2 sensitivity of laryngeal receptors appears to be diminished or abolished by carbonic anhydrase inhibition (Wang, 1994; Coates et al 1996) supports this hypothesis. In the present study, it was shown that the responses of CO 2 ‐sensitive fibres to two hypercapnic solutions with the same P CO2 but different pH values were similar in both direction and magnitude.…”