Beta-adrenergic receptor properties of a pulmonary alveolar type II cell preparation from the adult rat

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Abstract
The pulmonary alveolar type II cell synthesizes and secretes phosphatidylcholine (PC), a major component of surfactant, above basal level in response toβ-adrenergic stimulation. The investigation of the specific receptor which mediates these events was the topic of this study. Freshly isolated type II cells from adult rats were disrupted in a French pressure cell, and crude particulate fractions were recovered and used in assays for binding of the radioligand (−)-3-[125I]-iodocyanopindolol. The receptor had high affinity forβ-adrenergic agents, and specific binding to the receptor was saturable and reversible. The KD value obtained by kinetic means (19.6 pM) was in close agreement with that obtained by Scatchard (21.5 pM) and Hill (21.3 pM) analyses of steady-state binding data. The Scatchard correlation coefficients and Hill plot coefficients were close to 1, indicative of a single class of binding sites which displays no cooperativity. The specificity for catecholamine agonists and stereoselectivity observed were appropriate for aβ-adrenergic receptor. Use of selective drugs identified the presence of bothβ 1- andβ 2-adrenergic receptor subtypes (1:3, respectively) on this cell type.