Ga. Ferreyra et Da. Golombek, Rhythmicity of the cGMP-related signal transduction pathway in the mammalian circadian system, AM J P-REG, 280(5), 2001, pp. R1348-R1355
Citations number
55
Categorie Soggetti
Physiology
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
Entrainment of mammalian circadian rhythms requires the activation of speci
fic signal transduction pathways in the suprachiasmatic nuclei (SCN). Pharm
acological inhibition of kinases such as cGMP-dependent kinase (PKG) or Ca2
+/calmodulin-dependent kinase, but not cAMP-dependent kinase, blocks the ci
rcadian responses to light in vivo. Here we show a diurnal and circadian rh
ythm of cGMP levels and PKG activity in the hamster SCN, with maximal value
s during the day or subjective day. This rhythm depends on phosphodiesteras
e but not on guanylyl cyclase activity. Five-minute light pulses increased
cGMP levels at the end of the subjective night [circadian time 18 (CT18)],
but not at CT13.5. Western blot analysis indicated that the PKG II isoform
is the one present in the SCN. Inhibition of PKG or guanylyl cyclase in viv
o significantly attenuated light-induced phase shifts at CT18 (after 5-min
light pulses) but did not affect c-Fos expression in the SCN. These results
suggest that cGMP and PKG are related to SCN responses to light and underg
o diurnal and circadian changes.