Abstract
Abstract Rat serosal mast cell beta-adrenergic receptors were characterized both functionally by assessing changes in histamine release and cyclic 3',5' adenosine monophosphate (cAMP) levels and directly by radioligand binding studies using [3H]dihydroalprenolol ([3H]DHA), a beta-adrenergic antagonist. Mast cells were obtained by lavage of the pleural and peritoneal cavities of Sprague-Dawley rats and were purified on metrizamide gradients to greater than 95% purity. Resting mast cells stimulated with beta-adrenergic agonists demonstrate a marked rise in cAMP levels after a 15-sec incubation. However, the same concentrations of these agonists have no effect on IgE-mediated mast cell histamine release. [3H]DHA binding to intact mast cells is rapid, reversible, saturable, and stereoselective. The cells possess 40,000 +/- 14,000 beta-adrenergic receptors/cell and demonstrate a binding affinity of 1.58 +/- 0.56 nM for [3H]DHA. Competition studies reveal that 83.5% of the receptors are of the beta 2 subtype and 16.5% are beta 1. Neither sensitization with anti-DNP-BSA IgE nor subsequent challenge with specific antigen alters mast cell beta-adrenergic receptor characteristics. Rat mast cells possesses large numbers of high affinity beta-adrenergic receptors, primarily of the beta 2 subtype, coupled to adenylate cyclase, but the role of these receptors in mast cell secretory events is not yet established.
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