Isolation of plasma membranes from rat lungs: effect of age on the subcellular distribution of adenylate cyclase activity.

A simple and rapid method of isolating plasma membranes from rat lungs is described. The method involves homogenization of tissue in isotonic sucrose-buffered medium followed by differential and sucrose density gradient centrifugation. Plasma membranes obtained by this procedure were essentially free from other subcellular contamination. Plasma membranes isolated from 2-day-old rat lungs showed 6 to 7-fold purification of adenylate cyclase and 5'-nucleotidase activities compared to the original homogenate. In contrast, plasma membranes from 35-day-old rat lungs showed no purification of adenylate cyclase activity although 5'-nucleotidase activity showed similar enrichment. These results suggest that adenylate cyclase activity is not a reliable marker for plasma membranes from adult rat lungs.