Modulation of Ca2+ sensitivity by cyclic nucleotides in smooth muscle from protein kinase G-deficient mice.
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 approximately 80%. The initial peak was less inhibited (approximately 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 microm. Relaxation by cAMP (approximately 50% at 100 microm), Ca2+ sensitivity of force, and force potentiation by GTPgammaS 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.
Bonnevier
Johan
J
Department of Physiological Sciences, Martinsried, Munich 82152, Germany.
Fässler
Reinhard
R
Somlyo
Andrew P
AP
Somlyo
Avril V
AV
Arner
Anders
A
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002217:Carbachol / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000235:genetics* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009130:Muscle, Smooth / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D009711:Nucleotides / Q000737:chemistry; D013997:Time Factors
D009711:Nucleotides; D015124:8-Bromo Cyclic Adenosine Monophosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol; D000242:Cyclic AMP; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D002118:Calcium