Role of lysophosphatidylcholine in the desensitization of beta-adrenergic receptors by Ca(2+) sensitization in tracheal smooth muscle.

Lysophosphatidylcholine (Lyso-PC) is generally considered to promote tissue inflammation. To determine the involvement of exogenous Lyso-PC in the beta-adrenergic desensitization by phospholipase A2, we examined the inhibitory effects of isoproterenol (ISO) on tension and intracellular Ca(2+) concentration by methacholine (MCh) after continuous exposure to Lyso-PC in guinea-pig tracheal smooth muscle, using isometric tension recordings and fura-2 signal (F340/F380 ratio). Pre- exposure to 10 microM Lyso-PC markedly reduced subsequent inhibition by 0.3 microM ISO against 1 microM MCh-induced contraction in a time-dependent manner. In contrast, values of percent F340/F380 ratio for MCh with ISO were not affected after exposure to Lyso-PC. In the presence of Y-27632, a selective rho-kinase inhibitor, a reduction in subsequent relaxation by ISO after exposure to Lyso-PC was inhibited in a concentration-dependent manner. Preincubation with cholera toxin also inhibited reduced responsiveness to ISO by Lyso-PC. Pre-exposure to Lyso-PC did not attenuate subsequent relaxation by agents that bypass beta-adrenergic receptors. These results indicate that continuous exposure to Lyso-PC may cause homologous desensitization of beta-adrenergic receptors via an augmentation in sensitivity to Ca(2+) by rho, a small G protein, in airway smooth muscle, and that activation of the stimulatory G protein of adenylyl cyclase, G(s), may prevent this phenomenon.