Polarized effects of amiloride and 4,4′-diisothiocyano-stilbene-2,2′-disulfonic acid on ATP-induced contraction of trachea

Abstract

Polarity in the effects of amiloride and 4,4′-diisothiocyano-stilbene-2,2′-disulfonic acid (DIDS) in the guinea-pig isolated, perfused trachea was investigated to evaluate the roles of epithelial and airway smooth muscle Na + and Cl − channels in the development of contractile responses to ATP. The blockers were applied to the mucosal (intraluminal) perfusing solution or to the serosal (extraluminal) bath before the second of two challenges with ATP (10 −4 M), which was added to the same bath as the blocker, or to the abluminal bath. In epithelium-intact tracheas, amiloride (10 −4 M) added to the extraluminal or intraluminal bath rapidly (1 min) and extensively inhibited contractions to extraluminally applied ATP (10 −4 M). In contrast, contractions to intraluminally applied ATP (10 −4 M) were relatively resistant to extraluminal and intraluminal amiloride (10 −4 M), in terms of the degree and onset of the inhibition. DIDS (10 −4 M) present in the extraluminal or intraluminal baths caused a slowly developing elevation of baseline tone. After a 30 min incubation, extraluminal DIDS potentiated responses to extraluminally added ATP, but intraluminal DIDS inhibited contractions to ATP added to the extraluminal and intraluminal baths. In contrast to the intact tracheas where there was no difference, the second response of epithelium-denuded preparations to intraluminally administered ATP was diminished. In rubbed tracheas the response to intraluminally added ATP was inhibited further by intraluminal amiloride but was potentiated by intraluminal DIDS. The results suggest that the effects of amiloride and DIDS were polarized across the tracheal wall and involved epithelial and smooth muscle ion channels.