Involvement of calcium influx in muscarinic cholinergic regulation of phospholipase C in cerebellar granule cells.
Inositol phosphate accumulation on carbachol stimulation of rat cerebellar granule cells shows a marked dependence on factors affecting cytosolic Ca2+ concentration ([Ca2+]c). After 5 min, potassium depolarisation caused a modest accumulation of inositol phosphates but augmented the response to carbachol by a factor of 2-3. These effects of potassium were dependent on an extracellular source of calcium and could be partially blocked by specific (nifedipine) and nonspecific (verapamil) calcium channel blockers. Measurements of [Ca2+]c under a range of stimulatory conditions demonstrated a close correlation between the elevation of [Ca2+]c and agonist-stimulated phospholipase C (PLC) activity. The maximal potentiation of carbachol-stimulated inositol phosphate accumulation was achieved using 20 mM KCl, which increased [Ca2+]c from approximately 20 to approximately 75 nM, indicating the involvement of relatively low threshold Ca2+ channels and the high sensitivity of the relevant PLC to small changes in [Ca2+]c. By contrast, increases in [Ca2+]c induced by the Ca2+ ionophore ionomycin were associated with more modest and less potent effects on agonist-stimulated PLC. These results demonstrate a cooperative interaction between a receptor/G protein-regulated PLC and voltage-stimulated elevations of [Ca2+]c, which may function to integrate ionotropic and metabotropic signalling mechanisms in cerebellar granule cells.
Biochemistry Department, University of Dundee, Scotland.
E
E
del Río
D G
DG
Nicholls
C P
CP
Downes
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D016257:Fura-2; D007295:Inositol Phosphates / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D007295:Inositol Phosphates; D011976:Receptors, Muscarinic; D015759:Ionomycin; D011189:Potassium Chloride; D002217:Carbachol; D014700:Verapamil; D010738:Type C Phospholipases; D009543:Nifedipine; D002118:Calcium; D016257:Fura-2