Effects of potassium on laryngeal induced swallowing rate in rats.

Abstract

The swallowing reflex can be induced by peripheral stimulation of the larynx. Although previous studies have suggested that potassium ions exert facilitatory effects on the initiation of swallowing, little information is available on the mechanism underlying the potassium ion-evoked swallowing reflex. In this study, we evaluated the effects of potassium ions on peripheral afferent responses and the initiation of swallowing in conscious and anesthetized rats. Furthermore, the possible receptors involved were explored. The topical application of potassium chloride (KCl) significantly facilitated the swallowing reflex; these facilitatory effects were more prominent than those of distilled water (DW) or sodium chloride (NaCl). This phenomenon depended not on the concentrations of anions but on those of potassium ions. The potassium ion-induced response in the superior laryngeal nerve was most prominent after treatment with KCl, especially at the early stage. In chronic rats, without differences in licking behavior between DW, NaCl, and KCl, the intervals between swallows were the smallest during KCl-associated licking. Inward rectifier potassium channel (Kir)3.1- and Kir6.2-positive cells were detected in the nodose ganglion and vocal folds. The rate of expression of these molecules in immunoreactive cells was relatively high at 74.1% for Kir3.1 and 75.3% for Kir6.2. Kir3.1- and Kir6.2- blockers significantly decreased the number of KCl-induced swallows. Possible mechanisms underlying potassium ion-induced swallowing are discussed. Our findings suggest that Kir3.1 and Kir6.2 are involved in K ion-induced swallowing in rats.