CGMP Kinase

IP3 receptor associated cGMP kinase substrate of 130 kDa that is present in all smooth muscles and platelets. It s phosphorylation decreases calcium release from intracellular EP3-sensitive stores. 

The major relaxing transmitters are those that elevate the cAMP or cGMP concentration (Fig. 3). Adenosine stimulates the activity of cAMP kinase. The next step is not clear, but evidence has been accumulated that cAMP kinase decreases the calcium sensitivity of the contractile machinery. In vitro, cAMP kinase phosphorylated MLCK and decreased thereby the affinity of MLCK for calcium-calmodulin. However, this regulation does not occur in intact smooth muscle. Possible other substrate candidates for cAMP kinase are the heat stable protein HSP 20, (A heat stable protein of 20 kDa that is phosphorylated by cGMP kinase. It has been postulated that phospho-HSP 20 interferes with the interaction between actin and myosin allowing thereby smooth muscle relaxation without dephosphorylation of the rMLC.) Rho A and MLCP that are phosphorylated also by cGMP kinase I (Fig. 3). 

There has been isolated from mammalian tissue a protein kinase modulator which seems to inhibit cAMP protein kinases and to activate cGMP kinases (Kuo, 1975). Although not completely established, the modulator may be a single protein which alters the activity of both types of protein kinases in concert. This modulator seems to be, at least... 

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