The spasmogenic effects of vanadate in human isolated bronchus |
| |
Authors: | Julio Cortijo Victoria Villagrasa Miguel Martí-Cabrera Vicente Villar Joelle Moreau Charles Advenier Esteban J Morcillo Roger C Small |
| |
Affiliation: | Departament de Farmacologia, Facultat de Medicina i Odontologia, Universitat de València, Av. Blasco Ibañez 17, E-46010 Valencia, Spain;*Faculté de Médecine and Centre Hospitalier de Versailles, 78257 Le Chesnay, France;†Smooth Muscle Pharmacology Research Group, School of Biological Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, U.K. |
| |
Abstract: | - Inhalation of vanadium compounds, particularly vanadate, is a cause of occupational bronchial asthma. We have now studied the action of vanadate on human isolated bronchus. Vanadate (0.1 μM–3 mM) produced concentration-dependent, well-sustained contraction. Its −logEC50 was 3.74±0.05 (mean±s.e.mean) and its maximal effect was equivalent to 97.5±4.2% of the response to acetylcholine (ACh, 1 mM).
- Vanadate (200 μM)-induced contraction of human bronchus was epithelium-independent and was not inhibited by indomethacin (2.8 μM), zileuton (10 μM), a mixture of atropine, mepyramine and phentolamine (each at 1 μM), or by mast cell degranulation with compound 48/80.
- Vanadate (200 μM)-induced contraction was unaltered by tissue exposure to verapamil or nifedipine (each 1 μM) or to a Ca2+-free, EGTA (0.1 mM)-containing physiological salt solution (PSS). However, tissue incubation with ryanodine (10 μM) in Ca2+-free, EGTA (0.1 mM)-containing PSS reduced vanadate-induced contraction. A series of vanadate challenges was made in tissues exposed to Ca2+-free EGTA (0.1 mM)-containing PSS with the object of depleting intracellular Ca2+ stores. In such tissues cyclopiazonic acid (CPA; 10 μM) prevented Ca2+-induced recovery of vanadate-induced contraction.
- Tissue incubation in K+-rich (80 mM) PSS, K+-free PSS, or PSS containing ouabain (10 μM) did not alter vanadate (200 μM)-induced contraction. Ouabain (10 μM) abolished the K+-induced relaxation of human bronchus bathed in K+-free PSS. This action was not shared by vanadate (200 μM). The tissue content of Na+ was increased and the tissue content of K+ was decreased by ouabain (10 μM). In contrast, vanadate (200 μM) did not alter the tissue content of these ions. Tissue incubation in a Na+-deficient (25 mM) PSS or in PSS containing amiloride (0.1 mM) markedly inhibited the spasmogenic effect of vanadate (200 μM).
- Vanadate (200 μM)-induced contractions were markedly reduced by tissue treatment with each of the protein kinase C (PKC) inhibitors H-7 (10 μM), staurosporine (1 μM) and calphostin C (1 μM). Genistein (100 μM), an inhibitor of protein tyrosine kinase, also reduced the response to vanadate.
- Vanadate (0.1–3 mM) and ACh (1 μM–3 mM) each increased inositol phosphate accumulation in bronchus. Such responses were unaffected by a Ca2+-free medium either alone or in combination with ryanodine (10 μM).
- In human cultured tracheal smooth muscle cells, histamine (100 μM) and vanadate (200 μM) each produced a transient increase in intracellular Ca2+ concentration ([Ca2+]i).
- Intracellular microelectrode recording showed that the contractile effect of vanadate (200 μM) in human bronchus was associated with cellular depolarization.
- It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store. The Ca2+ release mechanism involves both the production of inositol phosphate second messengers and inhibition of Ca-ATPase. The activation of PKC plays an important role in mediating vanadate-induced contraction at values of [Ca2+]i that are close to basal.
|
| |
Keywords: | Vanadate, human airway smooth muscle, Ca2+ influx inhibitors, ryanodine, cyclopiazonic acid, ouabain, inositol phosphates, protein kinase C inhibitors, genistein, membrane potential |
|
|