Effects of five different organic calcium antagonists on guinea‐pig isolated trachea

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.

Section: Discussionmentioning

confidence: 99%

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

Turner

Power

Polak

et al. 1989

“…The maximum response observed with ET-1 is recorded for 10-10M, corresponding to 15.6 + 1.8% of the maximal tissue response obtained by addition of ACh 3 x 10-3M at the end of the experiment, indicating a high potency but a low efficacy of the peptide. This step involves calcium flux and suggests an effect dependent upon dihydropyridine-sensitive calcium channels (Lm channels, Nayler, 1988), since the contractile effect of ET-1 is enhanced by Bay K 8644 and inhibited by nicardipine, drugs which respectively increase and decrease the voltage-dependent calcium transfer in the guinea-pig or human airways (Foster et al, 1983a,b;Advenier et al, 1984;1986;Allen et al, 1985). This is emphasized by the results obtained in calcium-free medium where the contractile effect of ET-1 (10-0M) is markedly reduced, and to an extent similar to that of KCI (Advenier et al, 1986).…”

Section: Discussionmentioning

confidence: 99%

“…Then the preparation was immersed again in Ca2 + -free Krebs solution without EDTA, and after equilibration the contractile agents were added to the bath (Godfraind et al, 1968;Advenier et al, 1984). The effects of the contractile agents in Ca2+-free medium are expressed as a percentage of control contractions obtained in the presence of Ca2 +…”

Section: Methodsmentioning

confidence: 99%

Contractile activity of three endothelins (ET‐1, ET‐2 and ET‐3) on the human isolated bronchus

Advenier¹,

Sarriá²,

Naline³

et al. 1990

Self Cite

117

1 The effects of three endothelins: (i) the classical or human/porcine endothelin (ET-1); (ii) [Trp6, Leu7] endothelin (ET-2) and (iii) [Thr2, Phe4, Thr5, Tyr6, Lys7, Tyr'4] endothelin or rat endothelin (ET-3) were tested on the human isolated bronchus. 2 ET-1 produced a concentration-dependent contraction of the human isolated bronchus that proceeded in two different steps. The first step was observed at very low concentrations (pD2 = 11.01 + 0.17, n = 10) but corresponded to a low intrinsic activity (Emax = 15.6 + 1.8% of E,,,X induced by acetylcholine (ACh) 3 x 10-3M, n = 10). This effect was potentiated by Bay K 8644 10-7M (EX = 26.1 + 2.9% of ACh 3 x 10-3M, n = 5, P < 0.05), reduced by nicardipine 10-6M (Ex = 6.0 + 2.6% of ACh 3 x 10-3M, n = 5, P < 0.05) and strongly inhibited in calcium-free medium. The second step of the action of corresponded to a lesser potency (pD2 = 7.90 + 0.17, n = 9) but a higher intrinsic activity (E,,,, = 82.5 + 4.7% of ACh 3 x 10-3M). This effect was not significantly modified by nicardipine 10-6 M or by Bay K 8644 1V-7 M. Neither of the two effects was modified by indomethacin 3 x 10-6 M. 3 The effects of ET-2 and ET-3 were qualitatively similar to those of ET-1 but quantitatively different; for these two steps of contracting activity and for potency and efficacy the ranking was: ET-1 > ET-2 = ET-3. 4 Thus, ET-1 appears to be the most potent of these three substances in its effect on the human isolated bronchus. Its activity seems to involve the action of voltage-dependent calcium channels at low concentrations (10-12 to 10-9M), whereas other mechanisms are involved at higher concentrations (10-8 to 3 x 10-7M).

“…It has been shown previously that, in these preparations, the 'classical' calcium channel antagonists (e.g. verapamil, diltiazem, nicar-pidine) are able to inhibit K+-induced as well as Ca`-induced contractions at much lower concentrations than those required to inhibit the contractile effect of ACh and histamine (Advenier et al, 1984). On guineapig isolated trachea, as on the rabbit isolated aorta (Bertaccini et al, 1984), oxmetidine behaved as an antispasmogenic agent, its effect being independent of the type of stimulant employed to contract the preparation.…”

Section: Discussionmentioning

confidence: 99%

Relaxant effect of the H₂‐receptor antagonist oxmetidine on guinea‐pig and human airways

Advenier¹,

Gnassounou²,

Scarpignato

1987

1The effects of three different H2-receptor antagonists (cimetidine, ranitidine and oxmetidine) were tested on isolated preparations of guinea-pig trachea and human bronchus against contractions induced by acetylcholine, histamine and potassium chloride (KCl). In addition, their influence on calcium concentration-response curves in guinea-pig tracheal spirals was examined in a potassium-rich solution (30 mM). Finally, their effects were studied in vivo against acetylcholine and histamine-induced bronchoconstriction in anaesthetized guinea-pigs. 2 In guinea-pig isolated trachea, oxmetidine -in contrast to cimetidine and ranitidine, which were completely inactive -induced a concentration-dependent relaxation regardless of the excitatory stimulus: its -log EC, values (i.e. the negative log concentration that caused a 50% relaxation) were 3.46 + 0. 11, 4.61 ± 0.09 and 4.20 ± 0.12 against acetylcholine, histamine and KC1, respectively. In Ca2+-free, K+-enriched solution, the compound was able to inhibit Ca2"-induced contractions at concentrations close to those needed to counteract the spasmogenic effect of histamine in normal Krebs solution. Results obtained in the human bronchus preparation were similar to those observed in guinea-pig tracheal spirals. 3 When tested against acetylcholine or histamine-induced bronchoconstriction in vivo, oxmetidine (10 and 30 mg Kg-' intravenously) significantly reduced the increase in pulmonary airway resistance (Raw) induced by both agents. Once again, cimetidine and ranitidine were completely ineffective.4 In summary, oxmetidine displayed non-specific antispasmogenic activity on guinea-pig and human airways. This effect, which is independent of H2-receptor blockade, represents a side-effect of the drug which may be connected to its interference with Ca2" influx and the action or release of intracellular Ca2+.