Muscarinic receptor activation down-regulates the type I inositol 1,4,5-trisphosphate receptor by accelerating its degradation.
Stimulation of SH-SY5Y human neuroblastoma cells with carbachol, a muscarinic agonist, down-regulates the type I inositol 1,4,5-trisphosphate (InsP3) receptor by > 90% with maximal and half-maximal effects after approximately 6 h and approximately 1 h, respectively. Examination of the mechanistic basis of this down-regulation revealed that carbachol increased the rate of type I InsP3 receptor degradation (radiolabeled immunoprecipitable receptor was lost from cells with half-times of > 8 h and approximately 1 h in the absence and presence of carbachol, respectively) and that the concentration of type I InsP3 receptor mRNA, despite a transient decrease after 3 h, did not correlate with levels of the receptor. Only those muscarinic receptor subtypes coupled to stimulation of phosphoinositide hydrolysis were capable of causing type I InsP3 receptor down-regulation. Ca2+ mobilization was pivotal to the mechanisms of receptor down-regulation, since perturbation of Ca2+ homeostasis with either EGTA or thapsigargin blocked the ability of carbachol to accelerate receptor degradation. Studies with thapsigargin also revealed that both functional InsP3-sensitive Ca2+ stores and persistent elevation of InsP3 concentration were required for down-regulation to occur. In conclusion, phosphoinositidase C-linked muscarinic receptors down-regulate the type I InsP3 receptor by accelerating its degradation. It appears that this process is initiated by persistent discharge of intracellular Ca2+ stores via the channels formed by tetramerically complexed type I InsP3 receptors.
Wojcikiewicz
R J
RJ
Department of Cell Physiology and Pharmacology, University of Leicester.
Furuichi
T
T
Nakade
S
S
Mikoshiba
K
K
Nahorski
S R
SR
D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D006224:Cricetinae; D015536:Down-Regulation / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D009447:Neuroblastoma; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014162:Transfection; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010716:Phosphatidylinositols; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011976:Receptors, Muscarinic; D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D000252:Calcium-Transporting ATPases; D002118:Calcium