Isolated segments of guinea‐pig trachea or perfused tracheal tubes were arranged for the recording of trachealis tension changes in Krebs solution containing indomethacin (2.8 μm). In opened tracheal segments, epithelium removal caused modest (2–3 fold) potentiation of the effects of acetylcholine (ACh) and methacholine (MeCh) but failed to potentiate carbachol (CCh), bethanechol (BeCh), oxotremorine or KCl. Pretreatment with ecothiopate potentiated effects of ACh and MeCh but not of CCh or BeCh. Removal of epithelium in ecothiopate‐treated tissue potentiated effects of ACh and MeCh but not of CCh or BeCh. Guinea‐pig ileum challenged with ACh was used as a bioassay system for cholinesterase activity. Scrapings of tracheal epithelium did not hydrolyse ACh. Histochemical staining revealed no fibres positive for acetylcholinesterase or pseudocholinesterase in the tracheal epithelium. However, the underlying tissues contained acetylcholinesterase‐positive nerve fibres and the trachealis muscle itself stained positively for pseudocholinesterase activity. Neither tetrodotoxin (3 μm) nor hexamethonium (500 μm) modified the ability of epithelium removal to potentiate ACh. In perfused tracheal tubes where spasmogens were added to the luminal perfusate, epithelium removal potentiated effects of ACh (31 fold), CCh (10 fold), oxotremorine (2 fold) and KCl. In perfused tracheal tubes where spasmogens were added to the Krebs solution superfusing the adventitial surface of the tissue, epithelium removal significantly reduced the potency of CCh, oxotremorine and KCl. It is concluded that the selectivity and magnitude of the potentiation of cholinomimetics caused by epithelium removal depends on the route by which the cholinomimetic agent gains access to the trachealis muscle. The potentiation of acetic acid esters of choline seen in opened tracheal segments does not reflect the loss of epithelial cholinesterase activity and does not depend on the activity of nervous reflex arcs in the tracheal wall. The reduced potency of adventitially‐applied cholinomimetics and KCl seen in epithelium‐denuded tissue strongly suggests that the epithelium can moderate trachealis sensitivity to cholinomimetic agents not only by releasing epithelium‐derived relaxing factor but also by acting as a barrier to drug diffusion.

1 A low concentration (0.2 nM) of oxytocin induced phasic tension development in the isolated uterus of the day-22 pregnant rat. Tonic spasm was also induced by higher concentrations of oxytocin (2 and 20 nM). Spasmogenic responses to bradykinin and potassium chloride (KCI) also contained phasic and tonic components while acetylcholine induced tonic spasm only. 2 The phasic component of the responses to oxytocin and to bradykinin and both components of the response to KCI were inhibited by (+ )-cis diltiazem (0.1 and I JsM). The tonic component of the responses to oxytocin and to bradykinin and the responses to acetylcholine were only reduced by (+ )-cis diltiazem at concentrations >10O M. 3 (-)-cis Diltiazem was less potent than (+ )-cis diltiazem as an inhibitor of calcium (Ca2+)-induced spasm in a depolarizing medium and of the phasic spasms induced by oxytocin. The two isomers were of similar potency as inhibitors of oxytocin-induced tonic spasm. 4 Spasmogenic responses to oxytocin, bradykinin, acetylcholine and KCI were decreased when uteri were bathed in media which were Ca2+-free or of low Na+ content. However, there was no correlation between the rank order of sensitivity of the four spasmogens to the changed media and to their inhibition by (+ )-cis diltiazem. 5 Oxytocin (0.2 nM) increased the frequency, duration and amplitude of spike activity, measured by extracellular electrical recording, in parallel with enhancement of phasic tension development. With higher concentrations of oxytocin (2 and 20 nM) spike firing was initially continuous but often subsequently ceased despite the associated tonic contracture. After incubation in (+)-cis diltiazem (1OILM), oxytocin (0.2, 2 and 20 nM) produced graded tonic spasm without spike activity. 6 Oxytocin (0.2 nM) produced a small increase in 45Ca2+ influx into myometrium as assessed by the 'lanthanum method'. Higher concentrations of oxytocin (2 and 20 nM) did not increase 45Ca2" influx.7 It is concluded that the phasic component of the response of the uterus to oxytocin and bradykinin is associated with Ca2" influx via voltage-dependent Ca2+ channels. The tonic component is due to another mechanism(s) which does not appear to involve Ca2+ influx. All of the spasmogenic response to KCl can be explained by Ca2+ influx through voltage-dependent Ca2+ channels. These channels do not appear to be involved in the spasmogenic response to acetylcholine.

1 In guinea-pig isolated bronchus treated with indomethacin (2.8 gM), electrical field stimulation (EFS; 10 Hz, 0.5 ms, 60-70 V, for 10 s) evoked a tetrodotoxin (3 JM)-sensitive, biphasic contraction comprising a rapid, atropine (1 tLM)-sensitive cholinergic response succeeded by a slowly developing, capsaicin (10lM)-sensitive, non-adrenergic, non-cholinergic excitatory (NANCe) response.2 BRL 38227 (0.3-3 AM), salmeterol (0.003-3 pM) and ketotifen (1.0-300 AM) each produced concentration-dependent inhibition of both NANCe and cholinergic responses to EFS in guinea-pig isolated bronchus. 3 Substance P (SP; 1 ,M) and neurokinin A (NKA; 0.07 Mm) produced contractions equivalent in magnitude to the NANCe response to EFS, which were inhibited by salmeterol (1 pM), but not by BRL 38227 (3 Mm) or ketotifen (100 AM). 4 Acetylcholine (ACh; 6 AM) was equi-effective with the electrical activation of cholinergic neurones. BRL 38227 (3 AM) slightly inhibited responses to ACh (6 pM). Salmeterol (1 pM) and ketotifen (100 MM) markedly inhibited responses to ACh (6 Mm). 5 In bronchial rings pre-contracted with ACh (100 pM), BRL 38227 (0.1-30 pM), salmeterol (0.001-3tMM) and ketotifen (0.1-100 MM) each produced concentration-dependent relaxation. Unlike ketotifen, BRL 38227 and salmeterol only partially (18.8 ± 2.1% and 51.8 ± 3.9% respectively) reversed the ACh-induced contraction. 6 The (+ )-analogue of BRL 38227, BRL 38226 (0.3-100 MM), was without effect on responses to EFS and had no effect on the inhibition caused by BRL 38227. The K+-channel

1 Acetylcholine (ACh), histamine, prostaglandin E2 and potassium chloride (KCI) each evoked concentration-dependent spasm of guinea-pig isolated trachealis treated with indomethacin (2.8 tiM).2 Neither tetraethylammonium (TEA; 0.1-10mM) nor procaine (0.1-10mM) potentiated these spasmogens. Indeed, procaine (10mM) depressed the log concentration-effect curves of all the spasmogens while TEA (1-10 mM) caused some depression of the log concentration-effect curve of prostaglandin E2-3 Intracellular electrophysiological recording was performed in trachealis bathed by normal Krebs solution or by Krebs solution containing 2.8gM indomethacin. In either medium the majority of trachealis cells exhibited spontaneous electrical slow waves while some cells were electrically quiescent. In either medium the spasmogenic effects ofACh (1 mM) and histamine (0.2 mM) were accompanied by depolarization and abolition of slow wave discharge. In many cases the record of membrane potential subsequently exhibited noise which incorporated fast, hyperpolarizing transients. 4 In the absence and presence ofindomethacin, TEA (10 mM) and procaine (5 mM) markedly reduced the membrane noise and hyperpolarizing transients evoked by ACh or histamine without augmenting the evoked tension. 5 It is concluded that slow wave discharge does not depend on prostaglandin synthesis. The membrane noise and hyperpolarizing transients evoked by ACh and histamine represent the opening of membrane K+-channels. While such K+-channel opening may offset spasmogen-induced depolarization it does not moderate the evoked tension.