Endothelin‐induced contractions of tracheal smooth muscle and identification of specific endothelin binding sites in the trachea of the rat

Abstract

The presence of specific binding sites and the contractile activity of the novel peptide, endothelin have been investigated in rat trachea. Endothelin (10−8–10−5m) induced long‐lasting contraction of rat tracheal rings superfused with Krebs solution (EC50 5.4 × 10−6m). Contractions of the tissue to 10−6m endothelin were attenuated in Ca2+‐free medium containing 0.1 mM EGTA but unaffected by nicardipine (10−7m). After equilibration in Ca2+‐free medium (without EGTA) a return to normal Ca2+ concentrations (2.5 mm), 30 min or 60 min following endothelin (10−6m), produced a sustained contraction of the tissue. Specific binding sites for endothelin were identified on rat tracheal smooth muscle (KD 1.34 × 10−10m, maximal binding 1.2 fmol mm−2). Specific binding sites were also identified on nerve trunks. Endothelin binding was unaffected by co‐incubation with nicardipine (10−7m) or verapamil (10−7m). The discrepancy between the apparent KD for endothelin binding and the EC50 for endothelin‐induced contraction suggests that the endothelin binding sites identified in this study may not be associated with the receptors mediating contraction. These results indicate that endothelin binding sites are present on tracheal smooth muscle. The mechanism of endothelin‐induced contraction, whilst being dependent on extracellular calcium, does not appear to involve binding to the dihydropyridine‐ or verapamil‐sensitive sites on the voltage‐dependent Ca2+ channel. Its long duration of action may be associated with a sustained increase in Ca2+ permeability.

Inhibitory effects of nordihydroguaiaretic acid on ETA‐receptor‐mediated contractions to endothelin‐1 in rat trachea

“…Evidence supporting the involvement of protein kinase C in the spasmogenic actions of ET-l in rat isolated tracheal smooth muscle is provided by the findings in this study that an inhibitor of protein kinase C, staurosporine, attenuated ET-1-induced contractions in this tissue. However, it should be noted that staurosporine is not a specific inhibitor of protein kinase C (Ruegg & Burgess, 1989) Finally, the findings that NDGA, but not inhibitors of Land T-type Ca2'-channels, inhibited ET-1-induced contractions is entirely consistent with the view that these Ca2+-channels play no significant role in ET-1-induced contraction of rat tracheal smooth muscle (Turner et al, 1989;Henry, 1993) and moreover that NDGA-induced inhibition of contractions to were inhibited by NDGA, also developed very slowly in this preparation. Furthermore, the findings in the current study that NDGA inhibits ET-1-induced contractions via an action at the level of intracellular Ca2+-mobilisation concur with the proposal of Marsault and coworkers (1991) that the rate limiting step for the contractile action of ET-1 is a postreceptor event distal to the early changes in intracellular Ca2" levels.…”

Endothelin‐induced contraction and mediator release in human bronchus

“…For example, shortly after its discovery, ET-1 was reported to be a potent contractile agonist of guinea-pig trachea (Uchida et al, 1988). This observation has been confirmed (Hay, 1989;Maggi et al, 1989;Henry et al, 1990) and extended to isolated airway tissues from a variety of species including rat (Turner et al, 1989), ferret (Lee et al, 1990), rabbit (Grunstein et al, 1991) and man (Henry et al, 1990; Hemsen et al, 1990;Advenier et al, 1990;Brink et al, 1991;McKay et al, 1991). In fact, it has been proposed that the endothelins play a role in the pathophysiology of pulmonary disorders including asthma and pulmonary hypertension (Cernacek & Stewart, 1989;Mattoli et al, 1991a;Springall et al, 1991;.…”

Pharmacological modulation of endothelin‐induced contraction of guinea‐pig isolated airways and thromboxane release

“…Intense endothelin-like immunoactivity has been detected in the majority of airway epithelial (secretory and Clara cells, type II pneumocytes) as well as in airway smooth muscle cells (Turner et al, 1989;Rozengurt et al, 1990). Most of these cells are capable of synthesizing various eicosanoids (Robidoux et al, 1988) and probably PAF (Prevost et al, 1988).…”