Chronic activation of muscarinic and metabotropic glutamate receptors down-regulates type I inositol 1,4,5-trisphosphate receptor expression in cerebellar granule cells.
The ability of receptors coupled to phosphoinositide turnover to evoke accumulation of inositol 1,4,5-trisphosphate (InsP3) over extended incubation periods, and consequently to affect the level of InsP3 receptor expression, was studied in cultured cerebellar granule cells. The cholinergic agonist carbachol (CCh; 1 mM) evoked a biphasic accumulation of InsP3, a rapid three- to fourfold peak increase over control levels at approximately 10 s, decreasing within 1 min to a long-lasting plateau elevation. Using an antibody against the type I InsP3 receptor, it was demonstrated that > 50% down-regulation of type I InsP3 receptor expression in cerebellar granule cells occurred within 1 h of incubation with 1 mM CCh. Over 24 h, 1 mM CCh caused an approximately 85% decrease in type I InsP3 receptor levels, and significant decreases in immunoreactivity were evident at much lower concentrations of CCh. Direct assessment of total InsP3 receptor expression using a radioligand binding method also detected down-regulation, but to an apparently lesser extent. 1-Aminocyclopentane-1S,3R-dicarboxylic acid (200 microM), an agonist of metabotropic glutamate receptors, evoked a marked decrease in type I InsP3 receptors after 24 h of incubation. These findings demonstrate that a functional consequence of maintained InsP3 production in cerebellar granule cells is the down-regulation of InsP3 receptor expression and that this down-regulation may be a common mechanism of action of phosphoinositide-linked receptors during prolonged stimulation.
Department of Cell Physiology and Pharmacology, University of Leicester, England.
P B
PB
Simpson
R A
RA
Challiss
S R
SR
Nahorski
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D015536:Down-Regulation; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D018094:Receptors, Metabotropic Glutamate; D011976:Receptors, Muscarinic; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D002118:Calcium