The effect of beta-adrenargic agonists on Ca(2+) sensitivity in tracheal smooth muscle

Abstract

To determine whether a reduction in the sensitivity to Ca(2+) is involved in relaxation by beta-adrenergic receptor agonists, examined was correlation between force generation and intracellular Ca(2+) concentration in the inhibitory effects of isoproterenol (ISO) on methacholine (MCh)-induced contraction. Fura-2 was loaded in tracheal smooth muscle of guinea pigs and tension and fluorescence ratio F(sub 340)/F(sub 380) as an index of intracellular Ca(2+) concentration were recorded simultaneously. Addition of 0.3 muM ISO caused an inhibition in 1 muM MCh-induced contraction and a reduction in intracellular Ca(2+) concentration. The reduction in intracellular Ca(2+) concentration was, however, much smaller than that of tension. In conclusion, Ca(2+) sensitivity in addition to Ca(2+) influx plays an important role in beta-adrenergic action in airway smooth muscle.