Characterization of adenylyl cyclase isoforms in rat peripheral pulmonary arteries

Activation of adenylyl cyclase (AC), of which there are 10 diversely regula ted isoforms, is important in regulating pulmonary vascular tone and remode ling. Immunohistochemistry in rat lungs demonstrated that AC2, AC3, and AC5 /6 predominated in vascular and bronchial smooth muscle. Isoforms 1, 4, 7, and 8 localized to the bronchial epithelium. Exposure of animals to hypoxia did not change the pattern of isoform expression. RT-PCR confirmed mRNA ex pression of AC2, AC3, AC5, and AC6 and demonstrated AC7 and AC8 transcripts in smooth muscle. Western blotting confirmed the presence of AC2, AC3, and AC5/6 proteins. Functional studies provided evidence of cAMP regulation by Ca2+ and protein kinase C-activated but not G(i)-inhibited pathways, suppo rting a role for AC2 and a Ca2+-stimulated isoform, AC8. However, NKH-477, an AC5-selective activator, was more potent than forskolin in elevating cAM P and inhibiting serum-stimulated [H-3] thymidine incorporation, supporting the presence of AC5. These studies demonstrate differential expression of AC isoforms in rat lungs and provide evidence that AC2, AC5, and AC8 are fu nctionally important in cAMP regulation and growth pathways in pulmonary ar tery myocytes.