ALPHA(1)-ADRENERGIC AND MUSCARINIC RECEPTORS IN ADULT AND NEONATAL RAT TYPE-II PNEUMOCYTES

Binding characteristics of the alpha(1)-adrenergic radioloigand [H-3]p razosin, and the muscarinic cholinergic radioligand, [H-3]quinuclidiny l benzilate, were determined both in intact cell preparations of rat a lveolar type II pneumocytes (TIIPs) and in membrane preparations of ra t lung tissue. Binding in adult and neonatal (<24 h postnatal age) rat s was also compared. Binding affinities for both receptor classes on T IIPs and whole lung membrane preparations alike did not vary significa ntly with age. In lung membrane preparations, the concentrations of bo th receptor classes were higher in neonates than adults. In TIIPs, the alpha(1)-adrenergic receptor concentration was higher in neonates, bu t muscarinic receptor concentration was higher in adults. To begin inv estigation of the functional significance of these receptors, the effe cts of alpha(1)-adrenergic and muscarinic agonists on intracellular ca lcium ion concentration ([Ca2+](i)) were also measured. Both agonists induced consistent increases in [Ca2+](i), which were blocked by respe ctive antagonists. These data indicate the presence of receptors on TI IPs for alpha(1)-adrenergic and muscarinic agonists that may influence cellular function via modulation of [Ca2+](i).