The overall objective of this proposal is to characterize the adenosine receptor(s) and define the signal transduction mechanism(s) in allergic rabbit airways. An allergic asthmatic rabbit model has been developed by one of the co-investigators and will be used for the proposed studies. Inhaled adenosine induces bronchoconstriction in the allergic but not in normal rabbits. A finding similar to the humans where we and others have shown that adenosine induces a bronchoconstriction in asthmatics but not in normal subjects. In this rabbit model, theophylline, an adenosine receptor antagonist abolishes the adenosine induced bronchoconstriction suggesting that the specific adenosine receptors are involved in the bronchoconstrictor effect of adenosine. Our preliminary results support the existence of A1 adenosine receptor in this phenomenon. However, a pharmacological characterization is needed to substantiate this. Furthermore, it is unclear as to the role of epithelium and the involvement of second messenger(s) in the activation of A1 adenosine receptor. Thus, the central hypothesis that the activation of A1 adenosine receptor causes the bronchoconstriction in allergic airways (but not normal) via the interaction of adenosine with its receptor on smooth muscle initiates a signal which can be transduced via G protein(s) to modulate the activities of one or more effector enzymes (phospholipase C, adenylate cyclase and protein kinase C) and ultimately ionized calcium. Therefore, in the normal and allergic rabbits, we propose to study: (a) the adenosine receptor subtype by establishing the order of potency in vivo and in the presence and absence of epithelium to establish its involvement in airway constriction through in vitro binding and Western Blots (plasma membrane) and muscle bath studies; (b)possible coupling of the adenosine receptor to (3 protein using muscle bath studies, GDP release, GTPase activity and toxin induced ADP-ribosylation; (c) possible involvement of PIP2-PLC in the activation of adenosine receptor and whether it is coupled via G protein; (d) adenosine receptor activation on protein kinase C enzyme system; (e) calcium mobilizing effect of adenosine receptor activation in intact airway smooth muscle; (f) adenylate cyclase activity in response to adenosine receptor activation; and finally (g) messenger RNA using cDNA probes (Northern Blots). Ultimately, this proposal may help to explain how acquisition of allergic disorder contributes to the development of asthma, such as potential abnormalities in A1 adenosine receptor expression and its coupling to second messenger systems.
