Changes in activities of tryptophan hydroxylase and cyclic AMP-dependent and calcium-calmodulin-dependent protein kinases in raphe serotonergic neurons of 5,7-dihydroxytryptamine-treated rats.
It was reported that tryptophan hydroxylase was activated in vitro only under calcium-calmodulin-dependent phosphorylating condition, but not under cyclic AMP-dependent phosphorylating condition. This is attributed to the absence of cyclic AMP-dependent protein kinase in serotonergic neurons. Since we had evidence that in tissue slices of the raphe regions of rats both calcium-calmodulin-dependent and cyclic AMP-dependent processes may activate tryptophan hydroxylase in situ, we have investigated possibility of coexistence of calcium-calmodulin-dependent protein kinase and cyclic AMP-dependent protein kinase with tryptophan hydroxylase in rat raphe regions. The activities of cyclic AMP-dependent and calcium-calmodulin-dependent protein kinases were measured in the raphe serotonergic regions of rats treated intracisternally with 5,7-dihydroxytryptamine, which is a specific neurotoxin for serotonergic neurons. At 6 days after treatment with 200 ?g of 5,7-dihydroxytryptamine, activity of tryptophan hydroxylase and that of cyclic AMP-dependent protein kinase decreased by 60 and 40%, respectively, and a significant correlation was observed between the activities of the two enzymes. Calcium-calmodulin-dependent protein kinase activity disappeared in 5,7-dihydroxytryptamine-treated rats. These results suggest that both cyclic AMP-dependent and calcium-calmodulin-dependent protein kinases are present in raphe serotonergic neurons of rats, and may regulate tryptophan hydroxylase in vivo.
Sawada
M
M
Laboratory of Cell Physiology, Department of Life Chemistry, Graduate School at Nagatsuta, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 227, Japan.
Kanamori
T
T
Hayakawa
T
T
Nagatsu
T
T