A novel PDE1A coupled to M2AChR at plasma membranes from bovine tracheal smooth muscle.

Muscarinic antagonists, via muscarinic receptors increase the cAMP/cGMP levels at bovine tracheal smooth muscle (BTSM) through the inhibition of phosphodiesterases (PDEs), displaying a similar behavior of vinpocetine (a specific-PDE1 inhibitor). The presence of PDE1 hydrolyzing both cyclic nucleotides in BTSM strips was revealed. Moreover, a vinpocetine and muscarinic antagonists inhibited PDE1 located at plasma membranes (PM) fractions from BTSM showing such inhibition, an M(2)AChR pharmacological profile. Therefore, a novel Ca(2+)/CaM dependent and vinpocetine inhibited PDE1 was purified and characterized at PM fractions from BTSM. This PDE1 activity was removed from PM fractions using a hypotonic buffer and purified some 38 fold using two columns (Q-Sepharose and CaM-agarose). This PDE1 was stimulated by CaM and inhibited by vinpocetine showing two bands in PAGE-SDS (56, 58 kDa) being the 58 kDa identified as PDE1A by Western blotts. This PDE1A activity was assayed with [(3)H]cGMP and [(3)H]cAMP exhibiting a higher affinity as Km (µM) for cGMP than cAMP but being close values with V(max) cAMP/cGMP ratio of 1.5. The co-factor Mg(2+) showed similar K(A) (mM) for both cyclic nucleotides. Vinpocetine showed similar inhibition concentration 50% (IC(50) of 4.9 and 4.6 µM) for cAMP and cGMP, respectively. CaM stimulated the cyclic nucleotides hydrolysis by PDE1A exhibiting similar activation constant as K(CaM), in nM range. The original finding was the identification and purification of a vinpocetine and muscarinic antagonist-inhibited and CaM-activated PM-bound PDE1A, linked to M(2)AChR. A model of this novel signal transducing cascade for the regulation of cyclic nucleotides levels at BTSM is proposed.

Assays for cyclic nucleotide-specific phosphodiesterases (PDEs) in the central nervous system (PDE1, PDE2, PDE4, and PDE10).

Since the identification of phosphodiesterase activity in brain tissue more than 40 years ago, 11 distinct gene families have been identified, differing with respect to localization, regulation, affinity for cAMP and cGMP, and distinct functions within cells. PDEs 1, 2, 4, and 10 are currently of special interest to CNS pharmacology because of their high expression in specific areas of the brain and the behavioral effects of inhibitors of these enzymes in rodents. Efficient high-throughput PDE enzyme assays are essential for PDE-targeted drug discovery, and this unit details two types of assays. The first method is relatively inexpensive and is based on separating radiolabeled cNMPs from degradation products on alumina columns. The second method is fluorescence-based; it is fast and better accommodates high-throughput screening, but is more expensive. Although these methods have successfully been used for PDEs 1, 2, 4 and 10, they could be readily adapted to other PDEs.

Assay and purification of calmodulin-dependent cyclic nucleotide phosphodiesterase and isozyme separation.

In general, the action of intracellular second messengers, 3':5'-cyclic adenosine monophosphate (cAMP) and 3':5'-cyclic guanosine monophosphate (cGMP), are terminated by cyclic nucleotide phosphodiesterase (PDE). In most mammalian tissues, PDE exists in multiple forms that differ in subcellular localization, catalytic, regulatory, and immunological properties. One of these forms of enzyme is activated by Ca(2+) and calmodulin (CaM) and has a lower apparent K ( m ) for cGMP than for cAMP and higher V (max) for cAMP than for cGMP. This CaM-dependent cyclic nucleotide phosphodiesterase (CaMPDE) is widely distributed among mammalian tissues and other eukaryotes. CaMPDE is one of the most intensively studied and best characterized PDEs.