Epithelial modulation of trachealis muscle tension is calcium and temperature dependent

Resting tension affects eNOS activity in a calcium-dependent way in airways

The alteration of resting tension (RT) from 0.5 g to 2.5 g increased significantly airway smooth muscle contractions induced by acetylcholine (ACh) in rabbit trachea. The decrease in extracellular calcium concentration [Ca²⁺]_o from 2 mM to 0.2 mM reduced ACh-induced contractions only at 2.5 g RT with no effect at 0.5 g RT. The nonselective inhibitor of nitric oxide synthase (NOS), N^G-nitro-L-arginine methyl ester (L-NAME) increased ACh-induced contractions at 2.5 g RT. The inhibitor of inducible NOS, S-methylsothiourea or neuronal NOS, 7-nitroindazole had no effect. At 2.5 g RT, the reduction of [Ca²⁺]_o from 2 mM to 0.2 mM abolished the effect of L-NAME on ACh-induced contractions. The NO precursor L-arginine or the tyrosine kinase inhibitors erbstatin A and genistein had no effect on ACh-induced contractions obtained at 2.5 g RT. Our results suggest that in airways, RT affects ACh-induced contractions by modulating the activity of epithelial NOS in a calcium-dependent, tyrosine-phosphorylation-independent way.

Effect of temperature on muscarinic cholinoceptor-mediated phosphoinositide metabolism and tension generation in bovine tracheal smooth muscle

The effect of decreased temperature on phosphoinositide metabolism was studied in flurbiprofen pretreated bovine tracheal smooth muscle (BTSM) by investigating the consequences of cooling on muscarinic-cholinoceptor-mediated [3H]inositol phosphate ([3H]InsP) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) accumulation, basal phosphoinositidase C (PIC) activity and airways smooth muscle (ASM) tone. Cooling of [3H]Ins labelled BTSM slices from 37 degrees C to 27 degrees C for 20 min prior to the addition of agonist caused a substantial (73.0 +/- 2.5%) inhibition of carbachol (100 microM, 30 min)-stimulated [3H]InsP accumulation compared to values measured at 37 degrees C. The degree of inhibition of [3H]InsP accumulation was similar at all agonist time points (2-30 min) studied. In parallel experiments, cooling of unlabelled BTSM slices from 37 degrees C to 27 degrees C resulted in a 34% reduction in basal Ins(1,4,5)P3 mass (37 degrees C, 13.1 +/- 0.6 pmol mg-1 protein; 27 degrees C, 8.9 +/- 0.9 pmol mg-1 protein; P < 0.02) and markedly attenuated carbachol (100 microM)-stimulated increases in Ins(1,4,5)P3 accumulation. Basal PIC activity in the soluble fraction of BTSM homogenates, measured using a [3H]phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) /deoxycholate assay system, was also significantly lower at 27 degrees C compared to 37 degrees C (initial velocities of PtdIns(4,5)P2 hydrolysis of 853 +/- 167 (37 degrees C) and 418 +/- 119 (27 degrees C) pmol min-1 ml-1 (1/400 diluted) BTSM cytosol; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Explant culture of rabbit tracheobronchial epithelium: structure and prostaglandin metabolism

This study examines the potential usefulness of explant culture of rabbit tracheal epithelium as a model for the study of epithelial function under normal and potentially pathologic conditions. Accordingly, we assessed the structure and prostaglandin E2 (PGE2) release of tracheal epithelial explants obtained from adult pathogen-free rabbits. Epithelial cells attached to their native connective tissue substratum were maintained in culture for 5 days in serum-free medium, under bipolar conditions (air-liquid interface) on a permeable membrane (pore size, 0.2 mm), and nourished from the basolateral surface. At 5 days in culture, scanning and transmission electron microscopy and light microscopy demonstrated a pseudostratified, ciliated columnar epithelium with prominent folds and mucus secretion identical in appearance to the mucosa before culture. On the day of dissection (day 0) and after 4 days in culture (day 4), explants released PGE2 into the medium spontaneously. However, day 4 explants produced 3- to 4-fold greater amounts of PGE2 than day 0 explants. Moreover, day 4 explants demonstrated increased PGE2 release in response to bradykinin, a receptor-dependent agonist, and ionomycin, a calcium ionophore, while day 0 explants did not. Primary tracheal epithelial cell cultures grown to confluence (day 9) on a collagen substrate demonstrated PGE2 responses to bradykinin and ionomycin that qualitatively resembled those of day 4 explants. We conclude that rabbit tracheal explants cultured in vitro under the above conditions maintain cellular differentiation, in situ three-dimensional organization, and PGE2 synthetic pathways over several days in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Rabbit trachealis tension responses to receptor-mediated agonists are diminished by elastase

The present study examined the effects of elastase, in concentrations present in respiratory secretions, on airway smooth muscle contractile responses in vitro and the magnitude of the airway epithelial inhibition of smooth muscle tension. Experiments were performed on 126 full-thickness tracheal strips from 25 rabbits. Isometric tension responses to acetylcholine (10(-8) to 10(-4) M) and potassium chloride (10 to 110 mM) were examined before and after a 5-min exposure to either porcine pancreatic elastase (PPE) or human neutrophil elastase (HNE). PPE (5 to 40 micrograms/100 microliters) reduced the tension response to acetylcholine but had no effect on the tension response to potassium chloride. PPE and HNE (20 micrograms/100 microliters) produced similar effects. Mechanical removal of the epithelium per se significantly (P less than 0.005) decreased the ED50 response to acetylcholine but did not affect maximal tension. However, the airway epithelial inhibitory effect on the acetylcholine tension response was similar in the presence and absence of PPE (20 micrograms/100 microliters). These data suggest that the diminution of tracheal smooth muscle tension responses to receptor-mediated agonists induced by elastase is a direct effect on the muscle and is not mediated by an effect of elastase on the respiratory epithelium.

Effect of cooling on the responsiveness of canine tracheal muscle

Airway cooling causes bronchoconstriction in many persons who have asthma. To determine the direct effect of cooling on the response of tracheal muscle to parasympathetic and muscarinic stimuli in situ, the temperature of a segment of canine cervical trachea was adjusted to 37 degrees, 30 degrees, or 25 degrees C by superfusing temperature-controlled saline over its epithelial surface. The contractile response of the tracheal muscle to electrical stimulation of the vagus nerves and to intra-arterial acetylcholine was then determined. Cooling the segment to 25 degrees C decreased the contraction induced by parasympathetic stimulation. However, cooling did not alter the contraction induced by intra-arterial acetylcholine. Parallel studies were conducted in vitro using nine excised tracheal muscle strips taken from the same section of trachea in three additional dogs. Cooling the tracheal muscle to 25 degrees C in vitro increased the maximal contraction induced by both electrical field stimulation and by acetylcholine. Thus, cooling in situ does not alter the response of tracheal muscle to muscarinic stimuli and inhibits the response to parasympathetic stimuli. These data indicate that augmentation of the tracheal muscle response elicited by cooling in vitro does not reflect the response in situ. They suggest that a direct effect of cooling on airway smooth muscle response to parasympathetic and muscarinic stimuli does not account for cooling-induced bronchoconstriction in vivo.