Adenosine triphosphate (ATP) applied to the mucosal (intraluminal, "IL") compartment of the guinea-pig isolated, perfused trachea is more potent in evoking contraction of the smooth muscle than when it is applied to the serosal (extraluminal, "EL") surface - the epithelium (EPI) facilitates tracheal reactivity to ATP (Fedan et al., Pharmacologist 33:163, 1991). ATP and uridine triphosphate (UTP) stimulate CL(-) secretion with similar potency in normal and cystic fibrosis (CF) human nasal EPI, in the absence and presence of amiloride to block sodium absorption, and elevate [Ca2+]j (Mason et al., Br. J. Pharmacol. 103:1649, 1991). We compared the EL and IL reactivities of nucleotides as contractile agonists and examined the effects of blockage of ion transport pathways. ATP and UTP were more potent IL compared to EL. ATP EC50's (microM) were: 1.8, IL and 19.8, EL; UTP EC50's (microM) were: 3.5, IL and 141, EL. Thus, while IL ATP and UTP were nearly equipotent, EL UTP was approximately 7-fold less potent than EL ATP. The non-hydrolyzable ATP analog beta, gamma-methylene ATP (APPCP) had no contractile activity either IL or EL. The order of IL potency was ATP >/= UTP > APPCP; order of EL potency was ATP > UTP > APPCP. These relative potencies are unusual for nucleotide-induced contraction of smooth muscle. Amiloride [10(-4)M] inhibited IL and EL contractions to ATP and UTP in intact preparations and in those from which the EPI had been removed mechanically. In EPI-containing tracheae in the presence of amiloride, ATP and UTP were less potent IL compared to EL. Likewise, the Cl(-) channel blocker 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene [DIDS; 10(-4) M] inhibited IL and EL ATP- and UTP-induced contractions (+/-EPI). The nucleotides were less potent IL than EL in the presence of DIDS in intact tracheae. The effects of amiloride and DIDS were additive in that responses were abolished in the presence of both blockers. These findings indicate that Na+ and Cl(-) channels are involved in the contraction to ATP and UTP and in the facilitation of the response by the EPI. The lesser potency of UTP compared to ATP given EL indicates that UTP is more EPI-selective than ATP. Amiloride co-administered with nucleotides in CF to prevent Na+ absorption would be expected to reduce respiratory muscle contraction.
Respiratory-system-disorders; Pulmonary-system-disorders; Lung-disorders; Lung-function; Airway-obstruction; Airway-resistance; Laboratory-animals; Laboratory-testing; Throat; Mucous-membranes; Thorax; Muscle-contraction; Lung-cells; Lung-fibrosis; Phosphates; Nucleotides; Adenosines; Pharmacodynamics; Sodium-compounds; Chlorides; Ion-transport; Nasal-cavity; Dose-response