Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C59
Effect of purinergic and cholinergic costimulation on rat airway contractility
B. Mounkaila2, E. Roux1,2
1. Adaptation cardiovasculaire
Airway contractility plays a key role in obstructive respiratory dysfunctions. In airways, extracellular ATP can be coreleased with ACh. In isolated airways, cholinergic stimulation induces a short-time contraction followed by a slow delayed contraction . Extracellular ATP alone induces a transitory contractile response . The aim of this study was to investigate the combined effect of extracellular ATP (10µM) and cholinergic stimulation on the dynamics of airway contraction. Isometric tension was measured on tracheal (T), extra- (EB) and intrapulmonary (IB) bronchial rings form rats (Wistar, 8-15 week-old). The short-time phase was studied by simultaneous stimulation by ATP and low (0.3µM) and high (10µM) Carbachol (CCh) vs. CCh alone. Tension was expressed as % of reference contraction to 1mM ACh, and characterized by its maximal value (Fmax) and half-time to Fmax (T50). The delayed phase was studied by applying ATP on CCh-precontracted airways. Indo-1 fluorimetry was used to determine [Ca2+]i peak and plateau values and, when occurring, oscillation frequency in freshly isolated T myocytes costimulated with ATP and ACh (10µM) vs. ACh alone. Values are mean±SEM, compared by ANOVA. Significance was P<0.05. In T, EP and IP, costimulation with ATP+low CCh vs. low CCh significantly increased Fmax and decreased T50 (n=5). Fmax (CCh vs. CCh+ATP) was T: 22±18% vs. 34±5%; EB: 16±6% vs. 35±4% and IB: 15±4% vs. 56±4%. T50 (CCh vs. CCh+ATP) was T: 51±13s vs. 13±2s; EB: 34±7s vs. 5±3 and IB: 61±16s vs. 14±3s. ATP+high CCh vs. high CCh increased Fmax en T and EP, but not in IP rings, and did not modify T50 (n=8). Fmax (CCh vs. CCh+ATP) was T: 68±7% vs. 79±12% and EB: 81±13% vs. 97±13%. In myocytes, costimulation by ATP+ACh (n=42) vs. ACh alone (n=30) increased the peak and plateau values, but not the oscillation frequency. Peak and plateau values (ACh vs. ATP+ACh) were 446±52 nM vs. 633±50 nM and 25±29 nM vs. 53±48 nM, respectively. In CCh-precontracted rings (n=6), ATP induced a small transient contraction followed in T and EP but not IP by a progressive relaxation. Drop in tension 90 min after ATP vs. CCh alone was T: 57.1±0.86 %; EP: 42.7±8.06 %. The effect of ATP was not modified in the absence of epithelium (n=7). RB2 (P2Y antagonist) decreased the effect of ATP in EP and IP but not in T. alpha-beta-methylATP (P2X agonist) mimicked the effect of ATP in T and EB but not in IB. Adenosine had no effect. These data show that extracellular ATP has complex effects which depend on time and the position in the bronchial tree. It enhances the cholinergic short-time contraction by increasing the Ca2+ signal, and partially relaxes the sustained contraction in T and EB. They suggest that ATP acts directly on smooth muscle via P2X (in T and EP) and P2Y receptors (in EP and IB).
Where applicable, experiments conform with Society ethical requirements