Alpha1-adrenergic and muscarinic receptors in adult and neonatal rat type II pneumocytes

Binding characteristics of the ₁-adrenergic radioloigand [³H]prazosin, and the muscarinic cholinergic radioligand, [³H]quinuclidinyl benzilate, were determined both in intact cell preparations of rat alveolar type II pneumocytes (TIIPs) and in membrane preparations of rat lung tissue. Binding in adult and neonatal (<24 h postnatal age) rats was also compared. Binding affinities for both receptor classes on TIIPs and whole lung membrane preparations alike did not vary significantly with age. In lung membrane preparations, the concentrations of both receptor classes were higher in neonates than adults. In TIIPs, the ₁-adrenergic receptor concentration was higher in neonates, but muscarinic receptor concentration was higher in adults. To begin investigation of the functional significance of these receptors, the effects of ₁-adrenergic and muscarinic agonists on intracellular calcium ion concentration ([Ca²⁺]_i) were also measured. Both agonists induced consistent increases in [Ca²⁺]_i, which were blocked by respective antagonists. These data indicate the presence of receptors on TIIPs for ₁-adrenergic and muscarinic agonists that may influence cellular function via modulation of [Ca²⁺]_i.Offprint requests to: S. E. Keeney