Effects of carbonic anhydrase inhibition on the responsiveness of laryngeal receptors in cats to CO2

The effects of carbonic anhydrase inhibition on the responsiveness to CO2 o f pressure-sensitive laryngeal receptors were examined in anaesthetised, pa ralysed cats. Laryngeal CO2-sensitive receptors from the superior laryngeal nerve were selected by their responsiveness to intralaryngeal pressure and to perfusion of solution equilibrated with 9% CO2. The carbonic anhydrase inhibitor, methazolamide, when given intralaryngeally at 10(-4) m, diminish ed or abolished the responses to the CO2-equilibrated solution in four of s ix pressure-sensitive receptors. Histochemical staining for carbonic anhydr ase activity showed that the larynges perfused with methazolamide had dimin ished carbonic anhydrase activity, especially on the superficial layers of surface epithelium. Compared to untreated controls, when given intravenousl y (50 mg kg(-1)) methazolamide diminished or abolished the responses to CO2 of five of the six fibres studied. Histochemical staining of these larynge s showed no carbonic anhydrase reactivity at the sites of laryngeal recepto rs. These results suggest that the responses to CO2 of laryngeal pressure-s ensitive receptors are dependent on the presence of carbonic anhydrase. Inh ibition of laryngeal receptor carbonic anhydrase activity by methazolamide is more reliably achieved by systemic rather than by luminal administration .