Calcium/calmodulin-dependent protein kinase-II activation in rat pituitary cells in the presence of thyrotropin-releasing hormone and dopamine.
PRL release from rat lactotrophs in response to TRH is Ca2+ dependent. TRH-induced PRL release is inhibited either after repeated pulses of TRH or in the presence of dopamine. TRH, however, generates increases in intracellular Ca2+ concentrations ([Ca2+]i) in both conditions. Calcium/calmodulin-dependent protein kinase-II (CaM kinase-II) is a ubiquitous enzyme implicated in secretion. To determine whether down-regulation of CaM kinase-II activity caused the lack of responsiveness to increases in [Ca2+]i, we measured the generation of calcium/calmodulin-independent kinase activity. Anterior pituitary cells contain a 50-kilodalton form of CaM kinase-II, determined by immunoblot, and the enzyme is in lactotrophs, determined by immunocytochemistry. TRH rapidly and transiently increased calcium/calmodulin-independent kinase activity; the increase was maximal by 15 sec and returned to basal by 2 min. When TRH pulses (1 microM, 15 sec) were applied every 10 min, each pulse caused an increase in calcium/calmodulin-independent kinase activity of similar magnitude, and the activity returned to basal values between pulses. Pretreatment of cells with dopamine (1 microM; 30 min) inhibited PRL release, but did not prevent the increase in calcium/calmodulin-independent kinase activity. These results indicate that TRH still activates CaM kinase-II when PRL release is inhibited. Dopamine and repeated pulses of TRH must inhibit PRL release at a site after the TRH-induced increase in [Ca2+]i and at a site other than CaM kinase-II.
Cui
Z J
ZJ
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
Gorelick
F S
FS
Dannies
P S
PS
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004298:Dopamine / Q000008:administration & dosage / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D015151:Immunoblotting; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*
D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004298:Dopamine