Modulation of Ca2+ Sensitivity by Cyclic Nucleotides in Smooth Muscle from Protein Kinase G-deficient Mice

• Published in: The Journal of biological chemistry 2004-02, Vol.279 (7), p.5146-5151
• Main Authors: Bonnevier, Johan, Fässler, Reinhard, Somlyo, Andrew P., Somlyo, Avril V., Arner, Anders
• Format: Article
• Language: English
• Subjects: 8-Bromo Cyclic Adenosine Monophosphate - metabolism; Animals; Calcium - chemistry; Calcium - metabolism; Carbachol - metabolism; Carbachol - pharmacology; Cyclic AMP - metabolism; Cyclic GMP - metabolism; Cyclic GMP-Dependent Protein Kinases - genetics; Cyclic GMP-Dependent Protein Kinases - metabolism; Dose-Response Relationship, Drug; Guanosine 5'-O-(3-Thiotriphosphate) - metabolism; Mice; Mice, Knockout; Mice, Transgenic; Muscle, Smooth - metabolism; Muscles - metabolism; Nucleotides - chemistry; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M306532200

The cGMP-dependent protein kinase (PKG) is the main mediator of nitric oxide-induced relaxation of smooth muscle. Although this pathway is well established, the cellular action of PKG, nitric oxide, and cGMP is complex and not fully understood. A cross-talk between the cGMP-PKG and other pathways (e.g. cAMP-protein kinase A) seems to exist. We have explored cGMP- and cAMP-dependent relaxation of smooth muscle using PKG-deficient mice (cGKI–/–). In intact ileum strips of wild type mice (cGKI+/+), 8-Br-cGMP inhibited the sustained phase of carbachol contractions by ∼80%. The initial peak was less inhibited (∼30%). This relaxation was associated with a reduction in intracellular [Ca2+] and decreased Ca2+ sensitivity. Contractions of cGKI–/– ileum were not influenced by 8-Br-cGMP. EC50 for 8-Br-cGMP for PKG was estimated to be 10 nm. PKG-independent relaxation by 8-Br-cGMP had an EC50 of 10 μm. Relaxation by cAMP (∼50% at 100 μm), Ca2+ sensitivity of force, and force potentiation by GTPγS were similar in cGKI+/+ and cGKI–/– tissues. The results show that PKG is the main target for cGMP-induced relaxation in intestinal smooth muscle. cGMP desensitize the contractile system to Ca2+ via PKG. PKG-independent pathways are activated at 1000-fold higher cGMP concentrations. Relaxation by cAMP can occur independently of PKG. Long term deficiency of PKG does not lead to an apparent up-regulation of the cAMP-dependent pathways or changes in Ca2+ sensitivity.