Effects of various ion transport inhibitors on the water response in the superior laryngeal nerve in rats

Abstract

The effects of inhibitors [acetazolamide, an inhibitor of carbonic anhydrase; amiloride, an inhibitor of the Na channel; furosemide, an inhibitor of the Na/K/2Cl transporter; 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), an inhibitor of the Cl channel] on the water response in the superior laryngeal nerve (SLN) were investigated using whole nerve recordings from the SLN of anesthetized and paralyzed rats. Changes in spontaneous activity in the SLN after i.v. injection of a hypo- or hypertonic solution were also investigated. The water response to higher concentration amiloride solutions (0.1, 1, 5 and 10 mM) were significantly smaller in comparison with the control, i.e. the water response to deionized water (88-59% of the control, Fisher's PLSD, P < 0.05). DIDS suppressed the water response significantly at concentrations of 0.5 and 2 mM by 18 and 33%, respectively (P < 0.05). Likewise, acetazolamide (2 mM) and furosemide (5 mM) significantly suppressed the water response by 9 and 40%, respectively (P < 0.05). An i.v. bolus injection of a hypertonic solution (1 ml of 1.5 M NaCl or 1.0 M mannitol) depressed spontaneous activity of the SLN. In contrast, an i.v. injection of a hypotonic solution (0.015 M NaCl) increased spontaneous activity. These results suggest that several ion transporters and ion channels, as well as carbonic anhydrase, that may exist in the dorsal surface in the epiglottis may regulate the water response in the SLN and that osmotic changes in the dorsal surface of the epiglottis and in the interstitial space can affect nerve activity in the SLN.