Endothelin receptors and calcium translocation pathways in human airways

Abstract

Tension and phosphatidyl inositol (PI) turnover experiments were conducted to investigate the receptors and signal transduction pathways responsible for contractions elicited by endothelin (ET) ligands in human bronchus. Nicardipine (1 microM), the L-type calcium channel inhibitor, or incubation in Ca2+-free medium, produced marked inhibition of contractions to the ET(B) receptor-selective agonist, sarafotoxin S6c, and especially those induced by KCl. In contrast, Ca2+-free medium was without appreciable effect against contraction produced by endothelin-1 (ET-1), the non-selective ET(A) and ET(B) receptor agonist. In Ca2+-free medium, ryanodine (10 microM), which inhibits intracellular calcium mobilization, reduced sarafotoxin S6c- and ET-1-induced responses, but was without effect on responses to KCl. Similarly, nickel chloride (Ni2+; 1 mM) caused marked inhibition of contractions induced by sarafotoxin S6c or ET-1, but had no significant effect on KCI concentration-response curves. The mixed ET(A)/ET(B) receptor antagonist SB 209670 (3 microM) inhibited responses to sarafotoxin S6c and ET-1 such that concentration-response curves were shifted rightward, at the 30% maximum response level, by 10.0- and 3.8-fold, respectively, whereas BQ-123 (3 microM), the ET(A) receptor antagonist, was without effect on responses induced by either agonist. ET-1 (1 nM-0.3 microM) caused a concentration-dependent stimulation of PI turnover, whereas sarafotoxin S6c (0.3 nM-0.1 microM) induced only small and variable increases, except at the highest concentration. The increase in PI turnover evoked by ET-1 was inhibited by SB 209670 (3 microM), and also by BQ-123 (3 microM). This is consistent with linkage of ET(A) receptors to activation of inositol phosphate generation in human bronchial smooth muscle cells. Collectively, the data suggest that differences exist in the relative contributions of intracellular and extracellular Ca2+ mobilization mechanisms elicited by ET(A) and ET(B) receptor activation. Thus, sarafotoxin S6c-induced, ET(B) receptor-mediated contraction in human bronchial smooth muscle appears to be dependent, in part, upon extracellular Ca2+, although a significant component of the response was also mediated by intracellular Ca2+ release, including from ryanodine-sensitive stores. ET(A) receptor-mediated contraction of human airway smooth muscle was activated largely via the release of intracellular Ca2+.

Beyond the dogma: novel β2-adrenoceptor signalling in the airways

“…However, a recent study by DU et al [127] identified both RyR1 and RyR3 in murine ASM. Moreover, Ca 2+ release through these channels mediated agonist (carbachol)-induced tension development, a finding that was consistent with a previous report by HAY et al [128]. Taken together, these data suggest that RyR may represent novel targets for suppressing bronchoconstriction, although it should be noted that the effect of activation of the cAMP/PKA cascade on RyR function appears to be variable [126].…”

Ageing and epithelial integrity as modulators of airway smooth muscle responsiveness to endothelin-1

“…Evidence suggests that in rat tracheal smooth muscle, ET A receptor stimulation was associated with inositol phosphate generation, whereas ET B receptor activation results in the mobilization of extracellular Ca 2+ (Williams et al 1991;Henry 1993). More recent evidence has demonstrated that in human airway tissue, there are differences in the relative contribution of intracellular and extracellular Ca 2+ mobilization mechanisms elicited following ET A and ET B receptor activation (Hay et al 1999). In rat tracheal airway smooth muscle and lung alveoli, the ratio of ET A :ET B receptors is approximately 50:50, whilst in guinea-pig lung alveoli, ET A receptors comprise more than 80% of the total population (Goldie 1998).…”

“…It has previously been demonstrated that inositol phosphates are critical second messengers following ET receptor activation (Hay and Goldie 1997;Hay et al 1999). This was confirmed in the present study in guinea-pig and rat isolated tracheal tissue where ET-1 caused increases in inositol phosphate levels above basal in both the airway smooth muscle and cartilaginous regions of the trachea from the guinea-pig and rat.…”

“…The contractile effects of ET-1 in tracheal smooth muscle largely result from its direct action on cell surface receptors with the subsequent mobilization of intracellular and/or extracellular calcium pools (McKay et al 1996;Maxwell et al 1998aMaxwell et al , 1998b. The generation of intracellular inositol phosphates in airway smooth muscle from the human (Hay et al 1999) and from a number of animal species including rat Henry 1993), guinea-pig (Hay 1990) and sheep (Goldie et al 1994) is a prelude to contraction, although other indirect mechanisms may also contribute (see Goldie et al 1996 for review).…”

Interaction of KATP Channels and Endothelin-1 in Lambs With Persistent Pulmonary Hypertension of the Newborn

“…It produces its vasoactive effects through its interactions with at least two receptor subtypes, ET-A and ET-B, located on the vascular smooth muscle and endothelium. ET receptors are also present in other structures within the lung, such as fibroblasts, bronchial smooth muscle, and epithelial cells, but their respective distribution remains unknown (6). The pulmonary vasoconstrictor effect of ET-1 results mainly from activation of the ET-A receptor, whereas activation of the endothelial ET-B receptor has been shown to induce relaxation (5,7).…”