Cyclic nucleotide phosphodiesterases cGMP target

Cyclic GMP, like AMP, can be inactivated by a specific cyclic nucleotide phosphodiesterase to 5 -GMP. Similarly, the biological effects of cGMP are believed to involve a cGMP-dependent protein kinase, also known as protein kinase G (PKG) or G-kinase. The cellular targets for G-kinase-mediated relaxation are unknown in ASM, and do not appear to involve phosphorylation of MLCK. However, in vascular smooth muscle cGMP and thus G-kinase may be involved in the extrusion of Ca " from the cytosol (Suematsu etal., 1984 Popescu etal., 1985) and in sr Ca sequestration (Twort and van Breemen, 1988), ultimately leading to relaxation. 

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