Calcineurin inhibits desensitization of cloned rat 5-HT1C receptors.
Functional responses to stimulation of rat 5-HT1C receptors expressed in A9 cells were studied using whole cell voltage clamp recording technique. Stimulation of 5-HT1C receptors with serotonin (5-HT) evoked calcium-dependent outward currents of 109 pA in cells clamped at -50 mV. Pretreatment with the protein kinase C (PKC) activator phorbol myristic acetate (PMA) reduced the 5-HT-induced current amplitude by 46% of the control value. Inclusion of inositol triphosphate (IP3) in the pipette solution induced an outward current of 84 pA. The IP3-induced response was not affected by 60 min pretreatment with PMA. In the presence of the PKC antagonist calphostin C, 60 min treatment with PMA (10(-6) mol/l) reduced the 5-HT response only by 8%. In cells preincubated with PMA, injection of the calcium/calmodulin dependent serine proteinphosphatase calcineurin gradually increased the 5-HT-induced responses by 34%. In A9 cells which were incubated 24 h with the 5-HT1C receptor agonist meta chlorophenylpiperazine hydrochloride (mCPP), 5-HT-induced responses were reduced by 23% of the vehicle pretreated control value. Injection of calcineurin in mCPP treated cells enhanced the 5-HT-induced response by 24%. The results suggest that in A9 cells rat 5-HT1C receptors are desensitized after phosphorylation by PKC. This desensitization can be counteracted by calcineurin-induced dephosphorylation.
Boddeke
H W
HW
Sandoz Pharma Ltd, Basle, Switzerland.
Hoffman
B J
BJ
Palacios
J M
JM
Hoyer
D
D
D000818:Animals; D019703:Calcineurin; D002148:Calmodulin-Binding Proteins / Q000494:pharmacology*; D002460:Cell Line; D003001:Cloning, Molecular; D004594:Electrophysiology; D009281:Naphthalenes; D010749:Phosphoprotein Phosphatases / Q000494:pharmacology*; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D011083:Polycyclic Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002148:Calmodulin-Binding Proteins; D009281:Naphthalenes; D010879:Piperazines; D011083:Polycyclic Compounds; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; C061465:calphostin complex; D012701:Serotonin; D011493:Protein Kinase C; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; C015068:1-(3-chlorophenyl)piperazine