Cyclic nucleotide PDE-3. Quantitation of PDE-3A and -3B mRNAs in rat tissues by RNase protection assay

Type 3 cyclic nucleotide phosphodiesterase (PDE-3) isoforms exhibit a high affinity ("low K(m)") for cAMP and are specifically inhibited by cGMP and a number of pharmacological agents, which increase myocardial contractility, inhibit platelet aggregation, and increase smooth muscle relaxation. The PDE-3 family consists of at least two isozymes, PDE-3A (cardiac type) and PDE-3B (adipocyte type), with distinct tissue-specific distributions. PDE-3A mRNA is highly expressed in the cardiovascular system, whereas PDE-3B mRNA is primarily expressed in adipocytes and hepatocytes. Toward understanding potential roles of PDE-3 in diabetes mellitus, we have established a specific and sensitive RNase protection assay (RPA) for quantitating PDE-3A and PDE-3B mRNA in rat diabetic models. In fatty Zucker diabetic (ZDF) rats, PDE-3A mRNA, but not PDE-3B mRNA, was expressed in heart, whereas liver and white and brown fat tissues predominantly expressed PDE-3B mRNA. Unexpectedly, PDE-3B mRNA expression was approximately 2.5 times higher than PDE-3A mRNA in aorta from both ZDF and Sprague-Dawley (SD) rats. In contrast, expression levels of PDE-3A mRNA in heart were similar in both species. With this RPA, we were thus able to compare PDE-3A and -3B mRNA levels in different tissues as well as in different rat species.